Vin nghin cu nui trng thy sn I TS. Bi Quang T Bnh hc thy sn Nm 2006 Bnh hc thy sn 1 Bnh hc thy sn BIN SON: bI QUANG T vIN NGHIN CU NUI TRNG THU SN 1A CH: NH BNG-T SN-BC NINH in thoi: 0241 841934 & 0241 841 524 Mobile: 0912016959 E-mail buiquangte@sbcglobal.net Nm 2006 Bi Quang T2Li ni u Nuitrngthusnngycngcvtrquantrngtrongngnhkinht ca nc ta. c nng sut v sn lng tm, c, ba ba, cc a phng ng dng nhiu loi hnh nui tm, c v m rng din tch nui, do vic m bo cht lng sn phm v bnh ca tm, c, cc thu c sn khc c nhiu vn phtsinh.Trongmynmgny,bnhtm,cvccthucsnkhc xut hin nhiu vng trong c nc. Bnh gy nhiu tn tht cho phong tro nuitrngthusn.Snphmlmrakhngcthuhochhocchtlng gimkhngphcvchotiudngv xut khu, cho nn cng tc phng chng dch bnh cho nui trng thu sn ang i hi cp bch. gp phn hn ch nhng thit hi do bnh tm, c gy ra, chng ti binsoncunschBnhhcthusn.Cunschnhmphcvchocngtc gingdy,hctpcasinhvinchuynngnhnuitrngthusn,ngthi cung cp thng tin cn thit cho cn b nghin cu v bnh tm, c, cc c s sn xut tham kho. Ni dung ca cun sch c bin son da trn cc kt qu nghin cu v bnh tm, c ca nc ta trong thi gian qua, c bit t nm 1990 trliy.Bcccunschdatrncstiliuncngoivbnhc,bnh gip xc, bnh nhuyn th, bnh lng th, bnh b st,... bin son, tng bc bsungnhngktqunghincutrongnc.Quakinhnghimnghincuv trctipnuitrngthysn,chngtimnhdnvitchungccbnhcang vt thu sn thng gp Vit nam vo mt cun sch Bnh hc thy sn, gm cc ni dung sau: Phn 1: Tng quan v bnh hc thy sn Phn 2: Bnh truyn nhim ca ng vt thy sn Phn 3: Bnh k sinh trng ca ng vt thy sn Phn 4: Bnh dinh dng v mi trng ca ng vt thy sn Cunschcbinsonchokhootoksnuitrngthusn ,ngoi ra c th tham kho cho sn xutv nghin cu. Cun sch hon thnh nh s c v v to iu kin ca Vin Nghin cu nuitrngthusn1,HcVinkthutchu(AIT),Trngihcthu snNhaTrang,TrngihcnngnghipIvccbnngnghipchuyn nghin cu v bnh tm, c, nhn y chng ti xin trn thnh cm n. Cun sch ny chc chn cn nhiu hn ch, chng ti hy vng nhn c kin ng gp kp thi b sung sa cha tt hn. Nm 2006 Tc gi Bnh hc thy sn 3Mc lc Ni dungTrang Li ni u2 Mc lc3 Chng m u8 Phn 1: Tng quan v bnh hc thy sn11 Chng 1: Nhng khi nim c bn v bnh thy sn12 1. Bnh truyn nhim & bnh k sinh trng12 1.1. Bnh truyn nhim12 1.2. Bnh k sinh trng14 2. Bnh l20 2.1. S pht sinh v pht trin ca bnh20 2.2. Qu trnh c bn ca bnh l24 3. Mi quan h gia cc nhn t gy bnh cho thy sn32 3.1. Mi trng sng32 3.2. Mm bnh39 3.3. Vt ch39 3.4. Mi quan h gia cc nhn t gy bnh cho thy sn39 4. Phng php chn on42 4.1. iu tra hin trng42 4.2. Kim tra c th ng vt thy sn42 4.3. Thu mu c nh phn lp vi khun, nm virus, k sinh trng44 Chng 2: Nguyn l phng bnh tng hp cho nui trng thy sn45 1. Ti sao phi phng bnh cho ng vt thu sn45 2. Bin php phng bnh tng hp cho ng vt thu sn45 2.1. Ci to v ci thin mi trng nui ng vt thu sn 45 2.2. Tiu dit cc ngun gc gy bnh cho ng vt thu sn48 2.3. Tng cng sc khng bnh cho ng vt thu sn49 Chng 3: Thuc dng cho nui trng thy sn53 1. Khi nim v thuc dng trong nui trng thy sn53 2. Phng php dng thuc53 2.1. Phng php cho thuc vo mi trng nc54 2.2. Phng php trn thuc vo thc n55 2.3. Phng php tim thuc55 3. Tc dng ca thuc v cc nhn t nh hng n tc dng ca thuc55 3.1. Tc dng ca thuc55 3.2. Cc nhn t nh hng n tc dng ca thuc57 4. Ho cht v thuc dng phng tr bnh cho nui trng thu sn60 4.1. Ho dc60 4.2. Khng sinh65 4.3. Sulphamid68 4.4 . Vitamin71 4.5. Ch phm vi sinh72 4.6. Thuc v cy tho mc Vit Nam76 Danh mc thuc cm s dng v hn ch s dng85 Ti liu tham kho87 Bi Quang T4 Ni dungTrang Phn 2: Bnh truyn nhim ng vt thy sn88 Chng 4: Bnh virus89 1. Bnh xut huyt do virus c chp- SCV91 2. Bnh Herpesvirrus c chp- KHV94 3. Bnh xut huyt do virus c trm c GCRV96 4. Bnh xut huyt do virus c- VHS101 5. Bnh virus c tr sng- CCVD103 6. Bnh khi u t bo lympho106 7. Bnh Indivirus c bin109 8. Bnh hoi t thn kinh c bin- VNN110 9. Bnh MBV tm s114 10. Bnh m trng gip xc- WSSV119 11. Bnh u vng tm- YHD125 12. Bnh lin quan n mang ca tm- GAV129 13.Bnh nhim virus di da v hoi t mu- IHHVN134 14. Bnh Parvovirus gan tu tm- HPV136 15. Bnh hoi t mt ca tm138 16. Bnh ui - TSV141 17. Bnh BMN tm146 18. Bnh virus gy cht tm b m khi lu gi- SMVD148 19. Bnh ui trng ca tm cng xanh- WTD149 20. Bnh cua sa149 21. Bnh run chn cua150 22. Bnh mn rp mng o ca hu151 Chng 5: Bnh Rickettsia v Clamydia153 1. Bnh u nang biu b mang c153 2. Bnh Rickettsia v Clamydia tm155 3. Bnh run chn do Rickettsia cua157 Chng 6: Bnh vi khun159 1. Bnh nhim trng do vi khun Aeromonas spp. c nc ngt161 2. Bnh vi khun Vibrio VTS bin165 3. Bnh do vi khun Pseudomonas sp171 4. Bnh do vi khun Edwardsiella sp173 5. Bnh do vi khun gram dng- Streptococcus175 6. Bnh c c tm cng xanh177 7. Bnh do vi khun Mycobacterium180 8. Bnh vi khun dng si c182 9. Bnh bnh do vi khun dng si tm185 10. Bnh thi mang c nc ngt187 11. Bnh m trng do vi khun tm s188 Chng 7: Bnh do nm192 1. Bnh nm ht Dermocystidiosis195 2. Bnh nm ht- Ichthyophonosis198 3. Hi chng dch bnh l lot c- EUS201 4. Bnh nm mang c208 5. Bnh nm thu my c, tm nc ngt209 6. Bnh nm c tm nc mn213 Ti liu tham kho216 Bnh hc thy sn 5 Ni dungTrang Phn 3: Bnh k sinh trng ng vt thy sn220 Chng 8: Bnh k sinh trng n bo (Protozoa)- ng vt thy sn221 1. Bnh ngnh trng roi- Mastigophora222 1.1. Bnh trng roi trong mu- Trypanosomosis222 1.2. Bnh trng roi - Cryptobiosis224 1.3. Bnh trng roi- Costiosis225 2. Bnh do ngnh Opalinata227 Bnh- Protoopalinosis227 3. Bnh ngnh Dinozoa228 Bnh cua sa- Hematodinosis228 4. Bnh ngnh Haplosporidia232 4.1. Bnh bo t n bi k sinh trong mu ca hu- Bonamiosis232 4.2. Bnh bo t hnh cu a nhn Haplosporidiosis 235 5. Bnh ngnh Paramyxea239 5.1.Bnh Marteiliosis239 5.2. Bnh Mikrocytosis250 6. Bnh ngnh Apicomplexa253 Bnh Perkinsiosis253 7. Bnh do ngnh trng bo t- Sporozoa260 7.1. Bnh trng bo t- Gousiosis260 7.2. Bnh trng hai t bo- Gregarinosis263 8. Bnh do ngnh trng vi bo t- Mycrosporidia265 8.1. Bnh trng vi bo t c- Glugeosis265 8.2. Bnh tm bng- Microsporosis266 9. Bnh do ngnh bo t si- Cnidosporidia269 9.1. Bnh trng bo t si c 2 cc nang- Myxobolosis269 9.2. Bnh trng bo t si c ui- Henneguyosis272 9.3. Bnh trng bo t si c 1 cc nang- Thelohanellosis274 10. Bnh do ngnh trng lng- Ciliophora276 10.1. Bnh trng ming lch c nc ngt- Chilodonellosis276 10.2. Bnh trng ming lch c nc mn- Brooklynellosis278 10.3. Bnh trng lng ngoi k sinh- Hemiophirosis278 10.4. Bnh trng lng ni k sinh- Balantidiosis279 10.5. Bnh trng lng ni k sinh- Ichthyonyctosis281 10.6. Bnh trng lng ni k sinh- Inferostomosis283 10.7. Bnh trng qu da nc ngt- Ichthyophthyriosis286 10.8. Bnh trng lng nc mn- Cryptocaryonosis289 10.9. Bnh trng bnh xe290 10.10. Bnh trng loa kn294 10.11. Bnh trng ng ht298 Chng 9: Bnh do giun sn ng vt thy sn299 1. Bnh do ngnh giun dp- Plathelminthes301 1.1. Bnh do lp sn l n ch- Monogenea302 1.1.1. Bnh sn l n ch 16 mc- Dactylogyrosis302 1.1.2. Bnh sn l n ch mang c nc ngt- Ancyrocephalosis306 1.1.3.Bnhsnlnchrutnmangcncngt- Sundanonchosis 308 1.1.4. Bnh sn l n ch mang c bin309 1.1.5. Bnh sn l n ch con (18 mc)- Gyrodactylosis313 1.1.6. Bnh sn l song thn- Diplozoosis315 Bi Quang T6 Ni dungTrang 1.2. Bnh do lp sn l song ch- Trematoda317 1.2.1. Bnh sn l song ch- Aspidogastosis320 1.2.2. Bnh sn l song ch trong mu- Sanguinicolosis321 1.2.3. Bnh sn l song ch k sinh bang hi c- Isoparorchosis323 1.2.4. Bnh u trng sn l song ch k sinh mt c- Diplostomulosis325 1.2.5.Bnhutrngsnlsongchksinhtrongcthc- Clinostomosis 327 1.2.6. Bnh sn l song ch k sinh trong rut c- Carassotremosis328 1.2.7. Bnh sn l song ch k sinh trong rut c- Azygirosis329 1.2.8. Bnh u trng sn l gan nh c c- Clonorchosis330 1.2.9. Bnh u trng sn l gan nh c c- Opisthorchosis331 1.2.10. Bnh u trng sn l song ch mang c- Centrocestosis333 1.2.11. Bnh u trng sn l phi cua- Paragonimosis335 1.3. Bnh do lp sn dy- Cestoides336 1.3.1. Bnh sn dy khng phn t- Caryophyllaeosis v Khawiosis338 1.3.2. Bnh sn dy phn t- Bothriocephalosis339 1.3.3. Bnh u trng sn dy trong ni tng c- Diphyllobothriosis341 1.3.4. Bnh sn dy- Ligulosis342 2. Bnh do ngnh giun trn- Nemathelminthes343 2.1. Bnh giun trn- Philometrosis345 2.2. Bnh giun trn- Spironourosis347 2.3. Bnh giun trn- Spectatosis348 2.4. Bnh giun trn- Contracaecosis350 2.5. Bnh giun trn Spinitectosis351 2.6. Bnh giun trn- Camallanosis352 2.7. Bnh giun trn- Cucullanosis 353 2.8. Bnh giun trn- Cucullanellosis354 3. Bnh do ngnh giun u gai- Acanthocephala355 3.1. Bnh giun u gai- Rhadinorhynchosis358 3.2. Bnh giun u gai- Pallisentosis358 3.3. Bnh giun u gai- Neosentosis359 4. Bnh do ngnh giun t Annelida361 4.1. Bnh a c- Piscicolosis361 4.2. Bnh a- Trachelobdellosis362 4.3. Bnh a c su- 363 5. Bnh do ngnh nhuyn th- Mollusca364 Chng 10: Bnh do phn ngnh gip xc- Crustacea366 1. Bnh do phn lp chn cho- Copepoda367 1.1. Bnh gip xc chn cho- Ergasilosis367 1.2. Bnh gip chn cho- Sinergasilosis370 1.3. Bnh gip chn cho- Neoergasis372 1.4. Bnh gip xc chn cho- Paraergaslosis373 1.5. Bnh gip chn cho- Lamproglenosis374 1.6. Bnh trng m neo nc ngt- Lernaeosis375 1.7. Bnh trng m neo nc mn/l- Therodamosis380 1.8. Bnh rn c - Caligosis381 2. Bnh do b Branchiura383 2.1. Bnh rn c - Argulosis383 Bnh hc thy sn 7Ni dungTrang 3. Bnh do b chn u- Isopoda388 3.1. Bnh rn c- Ichthyoxenosis388 3.2. Bnh rn c- Alitroposis391 3.2. Bnh rn c - Coranallosis392 3.4. Bnh rn tm - Probopyrosis393 4. Bnh do gip xc chn t Cirripedia394 4.1. Bnh gip xc chn t ni k sinh tm cua394 4.2. Bnh sen bin k sinh cua gh- Dichelaspis400 4.3. Bnh sun bm trn ng vt thy sn402 Ti liu tham kho405 Phn 4: Bnh dinh dng v mi trng ca ng vt thy sn408 Chng 11: Bnh dinh dng409 1. Bnh dinh dng c409 2. Bnh dinh dng tm412 Chng 12: Bnh do mi trng413 1. Bnh do yu t v sinh413 2. Bnh do yu t hu sinh421 Chng 13: Sinh vt hi c, tm426 1. Thc vt hi c426 2. Gip xc chn cho hi c427 3. Sa gy hi trong ao nui tm428 4. Cn trng hi c430 5. C d n VTS435 6. Lng th n tm c437 7. B st n tm c428 8. Chim n tm c428 Ti liu tham kho439 Bi Quang T8chng M u 1. V tr, ni dung v nhim v ca mn bnh hc thu sn 1.1. V tr mn hc: Ngh nui trng thu sn trong my nm gn y pht trin rt nhanh. Mc ch ca ngi nui trng thu sn l thu c hiu qu cao nht, s dng mi iu kin c th huy ng c.Dovy,ccitngnuirtdbmcbnh.Ccyutmitrngchtlng nc xu, nhit khng thch hp, mt nui dy, thc n ngho, con ging khng m bo cht lng v qun l chm sc km lm cho ng vt thu sn b yu i, cc tc nhn gy bnh pht trin. ng thi do sng trong mi trng nc vi mt cao lm cho bnh c iu kin ly lan nhanh chng v gy thit hi ln. Vicnghincutmhiuccloibnhthusnvtmccbinphpphngtrbnhc hiu qu gp phn quan trng trong vic m bo v cht lng, sn lng ng vt thu sn nui. Trongnghnuitrngthusn,bncnhccmnhcchuynmnkhcnh:snxut ging, nui c tm thng phm, cng trnh,... th mn bnh ng vt thu sn l mt mn quan trng, nhm trang b cho cn b nui trng thu sn mt kin thc ton din to ra cc n c, n tm nui c sn lng cao v cht lng tt. 1.2. Ni dung mn hc: Chng trnh mn bnh hc thu sn gm cc ni dung sau: - Gii thiu nhng khi nim c bn v bnh truyn nhim v bnh k sinh trng. - Nhng khi nim c bn v bnh l ng vt thu sn - Gii thiu cc bin php tng hp phng tr bnh cho ng vt thu sn - Gii thiu mt s bnh ph bin v gy tc hi ln ng vt thu sn, c bit cc bnh Vit Nam, bao gm cc bnh: bnh truyn nhim do virus, vi khun, nm, bnh k sinh trng, bnh do dinh dng, bnh do mi trng, sinh vt hi c, tm. 1.3. Nhim v ca mn hc: Khi phong tro nui trng thu sn cha pht trin cc i tng nui ch yu l c, do bnh ch nghin cu trn i tng c v c tn l mn bnh c hc (Ichthyopathology). Sau thpk70trliyphongtronuitrngthusnphttrin,ngoiitngnuic, cc i tng khc c nghin cu nui: tm, cua, nhuyn th,... cho nn mn hc phi nghincuccbnhcangvtthusn(PathologyofAquaticAnimal)mipng c cho sn xut. Mn bnh hc ng vt thu sn c nhim v trang b cho hc vin nhng kin thc ton din v k thut nui trng thu sn ni chung v kin thc chuyn su: khi nim c bn v bnh hc, cc yu t lin quan n bnh, phng php chn on bnh, cc phng php phng tr bnh tng hp, nhng bnh thng gp gy nguy him cho ngh nui trng thu sn Vit Nam. Bnh hc thy sn 9II.Miquanhgiamnbnhhcthusnvicc mn hc khc - Lin quan n cc mn sinh hc c bn v c s: sinh hc i cng, ng vt hc, thc vt hc, thu sinh hc, vi sinh vt hc, ng loi hc,... - Lin quan n mn ho hc: v c, hu c, ho sinh, ho l,... -Linquannkthutnui:snxutgingthusn,nuithmcanhctmtrongao, lng b, cng trnh nui thu sn - Lin quan n ngnh th y, y hc III. Lch s ca mn bnhhc thu sn: 3.1.Trn th gii: T lu cc nh khoa hc m t mt s bnh c nh: cui th k 19 mt s tc gi xut bn cun sch hng dn bnh ca c nhng c bn vn m t cc tri chng lm sng l ch yu. Sang u th k 20 cc nh khoa hc th gii bt u nghin c v vit sch hng dn cc bnh c. Nm 1904, Bruno Hofer ngi c vit cun sch Tc nhn gy bnh c (Father of Fish Pathology) Vin s V.A.Dogiel (1882-1955) thuc Vin hn lm khoa hc Lin X c l ngi c cng ln ng gp nghin cu khu h k sinh trng c. ng vit phng php nghin cu k sinh trng c (1929); Bnh vi khun ca c (Bacterial Diseases of Fish) -1939. Nhngnm1930bnhtruynnhimcaccnghincutrongccphngth nghim. Nm 1949 cun sch gio khoa v bnh c hc c xut bn ln u tin Lin XcchbinltcgiE.M.Lyaiman.Tiptheolccthpk50v60cctcgi chuynnghincuvbnhcctiptcphttrinccnc:Bychowsky,Bauer, Mysselius, Gussev - Lin X c, Schaperclaus c, Yamaguti - Nht, Hoffman - M. Phongtronuitrngthusntrnthgiingycngphttrinmnhm,nhtlngh nui tm cc nc Chu - Thi Bnh Dng vo nhng nm ca thp k 80 th lch s bnh tm gn lin vi phong tro nui tm. Ktqunghincucctcnhngybnhchongvtthusnnnayrtphongph: bnh virus ca c n nay phn loi c hn 60 loi virus thuc 5 h c cu trc ADN hoc ARN. Bnh virus nhuyn th c 12 loi thuc 8 h, bnh virus gip xc c 15 loi tm v 3 loi cua thuc 5 h. Trong h Baculoviridae gp nhiu nht l 7 bnh Baculovirus. Vi khun gy bnh ng vt thu sn phn lp c vi trm loi vi khun gy bnh thuc9hvikhuninhnhlnhmvikhunAeromonasspp,Pseudomonassppgy bnh nc ngt v nhm Vibrio spp gy bnh nc mn. Nm gy bnh nc ngt: Saprolegnia, Achlya, Aphanomyces; nc mn: Lagenidium sp, Fusarium, Halipthoros sp, Sirolpidium. Ksinhtrngcangvtthusnnnaychngtaphnloicslngrtlnv phong ph. Ch tnh k sinh trng c nc ngt thuc khu vc Lin X c phn loi hn 2000 loi (1984-1985) Bi Quang T103.2.Vit Nam: Bmnbnhcchnhthnhtunm1960thuctrmnghincucncngt nhBng.NgithnhlputincabmnbnhclTinsHK,nguyncc trng Cc Bo v ngun li thu sn Vit Nam. n nay chng ta hnh thnh b mn hc phngnghincubnhhcthysn3vinI,II,IIIvcphngthnghimchnon bnh tm, c hin i i din cho ba min Bc, Trung, Nam v ven bin. mt s trng i hc c cn b ging dy nghin cu b mn bnh tm, c: Trng i hc thu sn Nha Trang, Trng i hc Cn Th, Trng i hc Nng Lm Th c.... n nay, chng ta c hng lot cc cng trnh cng b trn th gii v trong nc v kt qunghincubnhcangvtthusnVitNamtcuinm1960trliy: NghincuksinhtrngvbnhcacncngtminbcVitNamcaTinsH K:1961-1967;1969-1975,mt120loiksinhtrngtrongc42loiksinh trng,mtgingvmthphmiivikhoahc.Cngtrnhnghincukhuhk sinhtrngcamtsloicncngtngbngsngCuLongcaBiQuangTv ctv, 1984-1990; Nhng bnh thng gp ca c, tm nui ng bng sng Cu Long v bin php phng tr (Bi Quang T v ctv,1994). K sinh trng ca mt s loi c nc ngt ng bng sng Cu Long v nhng gii php phng tr chng ca Tin s Bi Quang T (2001) m t 157 loi k sinh trng, trong c 121 loi ln u tin c pht hin VitNam.BnhPenaeusmonodonbaculovirus(MBV)catms,nuicctnhpha Nam (Bi Quang T,1994). Nghin cu khu h k sinh trng c nc ngt min Trung v TyNguyn(NguynThMuivctv,1981-1985).Nghincumtsbnhchyutrn tmsnuikhuvcminTrungVitNam(ThHo,1997),....ChonnayVit Nam nghin cu bnh virus tm s l bnh Monodon Baculovirus (MBV), bnh vng u, bnh m trng. Cng trnh ln gn y l ti cp nh nc m s KN - 04 -12 t 1991-1995, do Tin s HKchnhimnghincu13bnhcatm,c.LnutinVitNamtptrung nghincuybnhvikhunviccnidungsau:phnlpvikhun,tcnhngy bnh, du hiu bnh, phn b v lan truyn bnh, bin php phng tr bnh. Nhng bnh nghin cu: bnh xut huyt m c trm c nui lng, bnh xut huyt c ba sa nui b, bnh hoi t do vi khun c tr, bnh hoi t m nu tm cng xanh, bnh pht sng u trng tm, bnh dc thn u trng tm, bnh vim nhim sau khi cy trai ngc. Nghin cu nguyn nhn gy cht tm cc tnh ven bin pha Nam (Nguyn Vit Thng, 1994-1999).Nghincubnhtruynnhimctrmcvcsongnuilngbin(Bi QuangT,1996-1998).cbitchngtaphnlpcvirusgybnhtmsnui nh bnh m trng (WSSV), bnh u vng (YHD) (Vn Th Hnh, 2001) Bnh hc thy sn 11Vin nghin cu nui trng thy sn I Bnh hc thy sn Phn 1 Tng quan vBnh hc thy sn Bin son: TS. Bi Quang T Nm 2006 Bi Quang T12Chng 1 nhng khi nim c bn v bnh hc thy sn 1. Bnh truyn nhim & bnh k sinh Trng. 1.1. Bnh truyn nhim. 1.1.1. nh ngha v bnh truyn nhim. Qu trnh truyn nhim l hin tng tng hp xy ra trong c th sinh vt khi c tc nhn gybnhxmnhp,tcnhngybnhlvisinhvt:virus,vikhun,nm,tonbo. Qu trnh truyn nhim thng bao hm ngha hp hn, n ch s nhim trng ca c th sinh vt, i khi ch s bt u cm nhim, tc nhn gy bnh ch kch thch ring bit, c trng hp khng c du hiu bnh l. Trong trng hp tc nhn xm nhp vo c th gybnhnhngchacduhiubnhl,lcnycthgicqutrnhtruynnhim song cha th gi l bnh truyn nhim. Bnh truyn nhim l phi km theo du hiu bnh l.Nhn t pht sinh ra bnh truyn nhim: - C tc nhn gy ra bnh truyn nhim nh: virus, vi khun, nm, to n bo... - Sinh vt c mang cc tc nhn gy bnh. -iukinmitrngbnngoithunlichosxmnhpcatcnhngybnhthc y qu trnh truyn nhim. Kch thc ca cc tc nhn gy bnh truyn nhim nhn chung b hn kch thc ca vt chvtnhimsongkhnnggybnhcachngrtln,ncthlmchovtchcht mt cch nhanh chng. Bnh truyn nhim gy tc hi ln cho vt ch do: - Sinh vt gy bnh c kh nng sinh sn nhanh nht l vius, vi khun ch sau my gi s lng ca chng c th tng ln rt nhiu tc ng lm ri lon hot ng sinh l ca c th vt ch. - Tc nhn gy bnh cn c kh nng lm thay i, hu hoi t chc m ng thi c th tit ra c t ph hoi t chc ca vt ch, lm cho cc t bo t chc hot ng khng bnh thng. 1.1.2. Ngun gc v con ng lan truyn ca bnh truyn nhim ng vt thu sn. 1.1.2.1. Ngun gc ca bnh truyn nhim ng vt thu sn . Trong cc thu vc t nhin: ao, h, sng v cc m, vnh ven bin thng quan st thy ngvtthusnbmcbnhtruynnhim,ngvtthusnbbnhldcht nhin. T mm bnh xm nhp vo cc ngun nc nui thu sn. ng vt thu sn b bnhtruynnhimvnhngxcngvtthusnbbnhchtlngungcchnhgy bnh truyn nhim. Tc nhn gy bnh truyn nhim ng vt thu sn sinh sn rt nhanh lm tng s lng n i vo mi trng nc bng nhiu con ng tu theo tc nhn gy bnh nh: theo cc vt lot ca c i ra nc qua h thng c quan bi tit, c quan tiu ho,cquansinhdchocquamang,xoangming,xoangmi.Ngoira,trongncc nhiu cht mn b hu c , nc thi cc nh my cng nghip, nc thi ca cc tri chn nuigiacm,giasc,ncthisinhhot,phnrc...cngtoiukinchobnhtruyn nhim pht sinh pht trin. Bnh hc thy sn 131.1.2.2. Con ng lan truyn ca bnh truyn nhim ng vt thu sn: - Bng ng tip xc trc tip: ng vt thu sn kho mnh sng chung trong thu vc cng vi ng vt thu sn mc bnh truyn nhim, do tip xc trc tip, tc nhn gy bnh truyn t ng vt thu sn bnh sang cho ng vt thu sn kho. - Do nc: Tc nhn gy bnh truyn nhim trong c th ng vt thu sn b bnh ri vo mi trng nc v sng t do trong nc mt thi gian, ly nc c ngun bnh vo thu vc nui thu sn, tc nhn gy bnh s ly lan cho ng vt thu sn kho mnh. - Do dng c nh bt v vn chuyn ng vt thu sn: Khi vn chuyn ng vt thu sn bnh v nh bt ng vt thu sn bnh, tc nhn gy bnh c th bm vo dng c, nudngdngcnynhbthocvnchuynngvtthusnkhothkhng nhng n lm ly lan bnh cho ng vt thu sn kho m cn ra mi trng nc. - Mm bnh truyn nhim t y ao: Cng vi cc cht hu c tn ti y ao, tc nhn gy bnh t ng vt thu sn mc bnh truyn nhim, t xc ng vt thu sn cht do b bnhrixungyaovtntimtthigian.Nuaokhngctydnvphi y k khi tin hnh ng nui thu sn, tc nhn gy bnh t y ao i vo nc ri xm nhp gy bnh truyn nhim cho ng vt thu sn. - Do ng vt thu sn di c: ng vt thu sn b bnh di c t vng nc ny sang vng nckhc,tcnhngybnhtruynnhimvovngncmi,gplciukinmi trngthayikhngthunlichoisngngvtthusn,tcnhngybnhxm nhp vo c th ng vt thu sn kho lm cho ng vt thu sn mc bnh. - Do chim v cc sinh vt n ng vt thu sn: Chim, c, ri c, ch, mo,....bt ng vt thu sn b bnh truyn nhim lm thc n, tc nhn gy bnh truyn nhim c th bm vochn,m,ming,vocthcachng,nhngsinhvtnylichuynbtngvt thu sn vng nc khc th tc nhn gy bnh truyn nhim t chng c th i vo nc, chchithunlichngxmnhpvocthngvtthusnkholmgybnh truyn nhim. 1.1.3. ng vt thu sn l ngun gc ca mt s bnh truyn nhim ngi v ng vt: C cng nh gip xc, nhuyn th....l ngun gc ca mt s bnh truyn nhim cho ngi vgiasc.Trongcthmtsngvtthusncmangvikhunbnhdchtnh: Clostridiumbotulinum,Salmonellaenteritidis,Proteusvulgaris,Vibrio parahaemolyticus...Ccloivikhunnycthtntitrncthvtrongmtsloi ng vt thu sn n c th ri vo nc v gy nhim bn ngun nc. Theo Prodnhian, Guritr bngthnghim khng nh Salmonella suipestifer,Salmonella enteritidis khi a vo xoang bng ca c n c th tn ti trong c th 60 ngy, n c th tn ti trong c p mui. Vi khun ny trong nc d dng theo nc vo rut c. Nguyn nhn ca ngi mc bnh dch t c th do n c sng hoc c nu nng cha chn c mang vi khun gy bnh nn truyn qua cho ngi. Theo A-K Serbina 1973 qua th nghim khng nh khi c mc bnh m c 15-20% s c c Clostridium botulinum. Tm,husngtrongmitrngncthisinhhot,ncthiccchungtrichnnui gia cm, gia sc, nc thi cc nh my, x nghip cng nghip. Ngi ta pht hin phn lnchngcmangvikhungybnhl,bnhngrut,bnhstphtban...Bngcon ng thc nghim ngi ta khng nh vi khun gy st pht ban c th sng trong c th hu n 60 ngy. T ngi ta chng minh dch st pht ban mt s nc nh: Php, M c quan h dng hu tm lm thc n. Do c, tm, hu v mt s hi c sn dngnsngcncchkimdchnghimkhctrnhmtsbnhlylancho ngi. Bi Quang T141.2. Bnh k sinh trng. 1.2.1. nh ngha: Trong t nhin c th sinh vt yu cu cc iu kin ngoi cnh c khc nhau do c nhiu chng loi c phng thc sinh sng ring, c s khc bit mi giai on pht trin. C mtssinhvtsngtdo,cmtssngcngsinh,trilicsinhvttrongtnggiai on hay c qu trnh sng nht thit phi sng bn trong hay bn ngoi c th mt sinh vt khc ly cht dinh dng m sng hoc ly dch th hoc t bo t chc ca sinh vt lmthcnduytrssngcanvphtsinhtchichosinhvtkiagilphng thc sng k sinh hay cn gi l s k sinh. Sinhvtsngksinhgilsinhvt k sinh.ng vt sng k sinh gi l k sinh trng. Sinh vt b sinh vt khc k sinh gy tc hi gi l vt ch. Vt ch khng nhng l ngun cung cp thc n cho k sinh trng m cn l ni c tr tm thi hay vnh cu ca n. Cc loi biu hin s hot ng ca k sinh trng v mi quan h qua li gia k sinh trng vi vt ch gi l hin tng k sinh. Khoa hc nghin cu c h thng cc hin tng k sinh gi l k sinh trng hc. 1.2.2. Ngun gc ca sinh vt sng k sinh: Thng ngun gc ca sinh vt sinh sng k sinh chia lm 2 giai on: 1.2.2.1. Sinh vt t phng thc sinh sng cng sinh n k sinh: Cng sinh l 2 sinh vt tm thi hay lu di sng chung vi nhau, c 2 u c li hay 1 sinh vtcli(cngsinhphinli)nhngkhngnhhngnsinhvtkia,2sinhvtsinh sng cng sinh trong qu trnh tin ho 1 bn pht sinh ra tc hi bn kia, lc ny t cng sinh chuyn qua k sinh, v d nh amp: Endamoeba histokytica Schaudinn sng trong rut ngididngthdinhdngnhlyccchtcnbtntikhnggytchicho con ngi lc ny n l cng sinh phin li, nhng lc c th vt ch do b bnh t bo t chc thnh rut b tn thng, sc khng yu, amp th dinh dng nh tit ra men ph hoi t bo t chc rut chui vo tng nim mc rut chuyn thnh amp th dinh dng ln c th gy bnh cho ngi. Nh vy t cng sinh amp chuyn qua k sinh. 1.2.2.2. Sinh vt t phng thc sinh sng t do chuyn qua k sinh gi n k sinh tht. Ttincaksinhtrngcthsinhsngtdo,trongqutrnhsngdo1chingu nhin, n c th sng trn b mt hay bn trong c th sinh vt khc, dn dn n thch ng vi mi trng sng mi, y c th tho mn c cc iu kin sng, n bt u tc hi n sinh vt kia tr thnh sinh sng k sinh. Phng thc sinh sng k sinh ny c hnh thnhthng do ngu nhin lp i lp li nhiu ln thng qua k sinh gi ri n k sinh tht. T tin ca sinh vt k sinh tri qua mt qu trnh lu di thch nghi vi hon cnh mi trng mi, v hnh thi cu to v c tnh sinh l, sinh ho ca c th c s bin i ln, 1 s c quan trong qu trnh sinh sng k sinhkhng cn thit th thoi ho hoc tiu gim nhcquancmgic,cquanvnng...Nhngcquanmbostnticani ging v i sng k sinh th pht trin mnh nh c quan bm, c quan sinh dc. Mt s ctnhsinhhcmichnhthnhvdndnnnhvditruynchoisau,qua nhiu th h cu to c th cng thch ghi vi i sng k sinh. 1.2.3. Phng thc v chng loi k sinh: 1.2.3.1. Phng thc k sinh: Da theo tnh cht k sinh ca k sinh trng chia: - K sinh gi: K sinh trngk sinh gi thng thng trong iu kin bnh thng sng t do ch c bit mi sng k sinh v d nh: Haemopis sp sng t do khi tip xc vi ng vt ln chuyn qua sng k sinh. Bnh hc thy sn 15- K sinh tht: K sinh trng trong tng giai on hay ton b qu trnh sng ca n u ly dinh dng ca vt ch, c th vt ch l mi trng sng ca n. Da vo thi gian k sinh c th chia ra lm 2 loi: -Ksinhctnhchttmthi:Ksinhtrngksinhtrncthvtchthigianrt ngn, ch lc no ly thc n mi k sinh nh ac Piscicola sp ht mu c . - K sinh mang tnh cht thng xuyn: Mt giai on, nhiu giai on hay c qu trnh sng k sinh trng nht thit phi k sinh trn vt ch.K sinh thng xuyn li chia ra k sinh giai on v k sinh sut i. +Ksinhgiaion: Ch mt giai on nht nh trong qu trnh pht trin k sinh trng sngksinh.Trongtonbqutrnhsngcaksinhtrngcgiaionsngtdo,c giai on sng k sinh nh: Ging gip xc chn t Sinergasilus giai on u trng sng t do, giai on trng thnh k sinh trn mang ca nhiu loi c. + K sinh sut i: Sut c qu trnh sng k sinh trng u sng k sinh, n c th k sinh trn mt vt ch hoc nhiu vt ch, khng c giai on sng t do nn tch khi vt ch l nbchtvdksinhtrngTrypanosomaksinhtrongrutac,ahtmuc chuyn qua sng trong mu c. Da vo v tr k sinh chia: Ngoi k sinh: K sinh trng k sinh trn b mt c th trong tng giai on hay sut i u gi l ngoi k sinh. c k sinh trng k sinh trn da, trn vy, trn mang, hc mi, xoangming,tmksinhtrnv,phnph,mangulngoiksinhvdnh Trichodina, Ichthyophthirius, Zoothamnium, Epistylis, Acineta, Argulus, Lernaea.... Ni k sinh: L ch k sinh trng k sinh trong cc c quan ni tng, trong t chc trong xoangcavtchnh:vibot(microspore)ksinhtrongccatm,snl Sanguinicolaspksinhtrongmuc;sndyCaryophyllaeussp,giunugai Acanthocephala k sinh trong rut c. Ngoi 2 loi k sinh trn cn c hin tng k sinh cp hai (siu k sinh), bn thn k sinh trng c th lm vt ch ca k sinh trng khc v d: sn l n ch Gyrodactylus sp k sinhtrncnhngnguynsinhngvtTrichodinaspliksinhtrnsnlnch Gyrodactylus sp. Nh vy sn l n ch Gyrodactylus l vt ch ca Trichodina nhng li k sinh trng ca c. Tng t nh trng m neo Lernaea k sinh trn c, nguyn sinh ng vt Zoothamnium sp k sinh trn trng m neo Lernaea. u trng giai on th ba ca giun trn Spironoura babei Ha Ky, k sinh trong rut tt ca sn l Amurotrema dombrowskajae Achmerov,giuntrnvsnluksinhtrongrutcacbng(Spinibarbichthys denticulatus). 1.2.3.2. Cc loi vt ch: C rt nhiu loi k sinh trng trong qu trnh pht trin qua nhiu giai on, mi giai on ccimhnhthicutovyucuiukinmitrngsngkhcnhaunncs chuyn i vt ch. Thng chia ra lm cc loi vt ch theo hnh thc k sinh ca k sinh trng. -Vtchcuicng:Ksinhtrnggiaiontrngthnhhaygiaionsinhsnhu tnh k sinh ln vt ch th gi l vt ch cui cng. - Vt ch trung gian: K sinh trng giai on u trng hay giai on sinh sn v tnh k sinh ln vt ch gi l vt ch trung gian. Giai on u trng v giai on sinh sn v tnh nu k sinh qua 2 vt ch trung gian th vt ch u tin l vt ch trung gian th nht cn vt ch tip l vt ch trung gian th 2. Bi Quang T16- Vt ch bo trng (lu gi): C mt s k sinh trng k sinh trn nhiu c th ng vt, loingvtnycthtrthnhngungcgintipcmnhimksinhtrngcho ng vt kia th gi l vt ch bo trng v d sn l Clonorchis sinensis Cobbold, 1875 giai on u trng k sinh trong c th vt ch trung gian th nht l c Bithynina longiornis v vt ch trung gian th 2 l cc loi c nc ngt. Giai on trng thnh k sinh trong gan, mt vt ch cui cng l ngi, mo, ch v mt s ng vt c v. ng v quan im k sinh trng hc ca ngi th ch mo l vt ch bo trng. Do mun tiu dit bnh sn l gan th khng nhng dit vt ch trung gian m cn dit vt ch bo trng. V d i vi c k sinh trng Cryptobia branchialis k sinh trn mang c trm gy bnh mangnghimtrngnhngcngloinybmtrnmangcmtrng,cmhoavis lng nhiu hn c Trm, c M vn khng b bnh do 2 loi c ny bn thn c kh nng mindchtnhin.TrnghpnycMlvtchlugi(botrng)cabnh Cryptobiabranchialis.Trongccaonuicthngnuighpnhiuloicnnmun phngbnhCryptobiabranchialischocTrmphikimtracnthnccloiccng nui x l tiu c cc vt ch lu gi mi phng bnh cho c trm c trit . 1.2.4. Phng thc nhim ca k sinh trng. K sinh trng nhim ch yu bng 2 con ng. 1.2.4.1.Nhim qua ming: Trng, u trng, bo nang ca k sinh trng theo thc n, theo nc vo rut gy bnh cho c nh: k sinh trng bo t trng Goussia sp, giun trn Capilaria sp. 1.2.4.2. Nhim qua da: K sinh trng qua da hoc nim mc c cn qua vy v mang i vo c th gy bnh cho vt ch, nhim qua da c 2 loi: - Nhim qua da ch ng: u trng ch ng chui qua da hoc nim mc vo trong c th vt ch, v d u trng sn l Posthodiplostonum cuticola c thng da v chui vo lp di da tip tc pht trin. - Nhim qua da b ng: K sinh trng thng qua vt mi gii vo c da ca vt ch k sinh gy bnh v d: K sinh trng Trypanosoma sp. Nh a c c thng da ht mu c k sinh trng t rut a vo mu c. 1.2.5. Mi quan h gia k sinh trng, vt ch v iu kin mi trng. K sinh trng, vt ch v iu kin mi trng c quan h vi nhau rt mt thit. Quan h gia k sinh trng vi vt ch ph thuc vo giai on pht trin, chng loi, s lng k sinh trng, v tr k sinh v tnh trng c th vt ch. iu kin mi trng sng ca vt ch nh hng trc tip hoc gin tip n k sinh trng, vt ch v mi quan h gia chng vi nhau. 1.2.5.1. Tc ng ca k sinh trng i vi vt ch: K sinh trng khi k sinh ln vt ch gy hu qu tc hi mc tuy c khc nhau nhng nhnchunglmchocthvtchsinhtrngchm,phtdckhngtt,sckhng gim c th b cht. C th tm tt nh hng ca k sinh trng i vi vt ch nh sau: Tc ng kch thch c hc v gy tn thng t bo t chc: y l loi tc dng thng thng nht ca k sinh trng i vi vt ch nh ban m giun kim b ra quanh hu mn lmchongicgiunkimksinhngangykhchu.RncArgulusdngcquan ming v gai bng co ln da c kch thch lm cho c kh chu bi li lon x hoc nhy ln mt nc. Bnh hc thy sn 17Ksinhtrnggytnthngcctchccquanvtchhintngnyrtphbin nhngmcckhcnhaunugytnthngnghimtrngcthlmchotnhhon chnh ca cc c quan b ph hoi, cc t bo bong ra gy thnh so, t chc b t mu v tit ra nhiu nim dch v d nh: sn l n ch gip xc k sinh trn da v mang c ph hoi t chc da v mang. Tc ng nn v lm tc: C mt s k sinh trng k sinh cc c quan bn trong lm chomtstchctbobteonhlihocbtlitricht,loitcdngnythng thy t chc gan, thn, tuyn sinh dc nh Sn dy Ligula sp, k sinh trong xoang h c Chp lm cho tuyn sinh dc ca c ch pht trin n giai on II. Mt s k sinh trng k sinh c th chn p mt s c quan quan trng nh tim, no...dn n lm cho vt ch cht nhanh chng. K sinh trng k sinh s lng ln trong rut c th lm tc rut ca c nh Acanthocephala sp, Bothriocephalus sp. C mt s k sinh s lng t nhng n c th kch thch dy thn kinh dn n co git cng gy nn tc nghn rut, tc ng tnh mch. Tc ng ly cht dinh dng ca vt ch: Tt c k sinh trng thi k k sinh u cn cht dinh dng t vt ch, v vy nn nhiu hay t vt ch u b mt cht dinh dng gy tn hi cho c th. Tuy nhin, vi s lng k sinh t hu qu khng thy r ch khi no k sinhtrngksinhvislngnhiumibiuhinrrt.QuanghincuhcTm Acipenseridae,snlnch Nitzschia sturionis k sinh, mi ngy 1 con sn l n ch ht 0,5 ml mu, lc cm nhim nghim trng c th m c 300-400 con sn l nh vy 1conctrong24gimtikhong150-200mlmulmchocgyimauchng.K sinhtrngLernaeaksinhtrncm,ctrmslngnhiudohtmumcrtgy thng thy u rt to, bng v ui tht li nu khng x l lu c s cht. Tcnggycvivtch:Ksinhtrngtrongqutrnhksinhtinhnhtraoi cht, bi tit cht cn b ln c th vt ch ng thi k sinh trng tit ra cht c gy c cho vt ch. Qua kt qu nghin cu k sinh trng c nhiu ti liu cho bit rn c Argulus mingctuyntbockhnngtitradchphhoitchcdavmangc,ksinh trngSinergasilusksinhtrnmangnhiuloicncngtntitrachtlmtanrt chc mang, k sinh trng Cryptobiabranchialis k sinh trn mang c cng tit ra c t phhoitchcmang.achtmuctitramenchngngmu,ksinhtrng Trypanosoma sp c men lm v t bo hng cu. Lm mi gii gy bnh: Nhng sinh vt k sinh ht mu thng lm mi gii cho mt s k sinh trng khc xm nhp vo c th vt ch v d: a c ht mu c thng mang mt s k sinh trng ly cho s c kho mnh. 1.2.5.2. Tc dng ca vt ch i vi k sinh trng: Vn tc dng ca vt ch i vi k sinh trng rt phc tp, ivi ng vt thu sn nghin cu v vn ny cha nhiu nn s nh hng tht c th kh c th kt lun chnh xc. Nhn chung tc dng ca vt ch i vi k sinh trng biu hin cc mt di y: Phn ng ca t bo t chc vt ch: K sinh trng xm nhp vo c th vt ch gy kch thch lm cho t bo t chc c phn ng. Biu hin ni k sinh trng i vo t chc m hnh thnh bo nang hoc t chc xung quanh v tr k sinh c hin tng t bo tng sinh, vim lot hn ch sinh trng v pht trin ca k sinh trng, mt khc lm cho c quan bm ca k sinh trng km vng chc hn ch tc hi ca k sinh trng, c lc c th tiu dit k sinh trng vi d: k sinh trng qu da Ichthyophthiriuskhi k sinh trn da c, da ca vt ch nhn kch thch, t bo thng b tng sinh bao vy k sinh trng thnh cc bctrnglmtmnncngilbnhbchim.Snlksinhtrndacvcl Bi Quang T18Posthodiplostonrum cuticola hnh thnh bo nang, vch c t bo sc t en bao vy nn da c c cc ht lm tm en. Phnngcadchth:Vtchnhnkchthchkhicksinhtrngxmnhpvosn sinh ra phn ng dch th. Phn ng dch th c nhiu dng nh: pht vim, thm thu dch phalongccchtc,vatng kh nng thc bo lm sch cc d vt v t bo cht ca bnh. Nhng phn ng dch th ch yu l sn sinh ra khng th, hnh thnh phn ng min dch. Phn ng min dch ca c th vt ch trc y ngi ta cho rng ch c cc bnh do vi sinh vt gy ra nhng qua kt qu nghin cu gn y k sinh trng thuc cc ngnh: Nguyn sinh ng vt, giun sn, gip xc k sinh...c th vt ch cng c kh nng sn sinh ra min dch chng qua kh nng min dch yu hn. Tui ca vt ch nh hng n k sinh trng: Thng vt ch trong qu trnh pht trin thcthtngtrng,ksinhtrngksinhtrncthvtchcngcsthayicho thch hp. i vi k sinh trng chu k pht trin c vt ch trung gian thng xy ra 2 hng: -Mtsgingloiksinhtrngksinhtrncthvtchccngvtlnhim gimitheostnglncatuivtchvdsndyBothriocephalusgowkongensisk sinh trong rut c trm c thng c di 1 tui c t l v cng nhim cao, do c trm c giai on c hng n thc n ch yu l sinh vt ph du trong c Cyclops l vt ch trung gian ca sn dy trn, c trm c trn 1 tui t l nhim thp do n c. - Mt s k sinh trng k sinh c cng v t l tng ln theo tui ca vt ch do lng thcntnglmtrongthcnvtchtrunggiancngtngtheo,thigiancngdikh nngtchtvchinhimbnhcngnhiuvvyclnthngccngvtl nhim k sinh trng cng cao. K sinh trng l ngoi k sinh thng t l v cng nhim ph thuc vo din tch tip xc, c th vt ch cng ln k sinh trng k sinh cng nhiu hoc thi gian sng ca vt ch cng lu th k sinh trng k sinh cng nhiu. Do cu to c th, mi trng sng ca c con v c ln khc nhau dn n c s sai khc gia t l v cng nhim ca k sinh trng. Mt s k sinh trng pht trin khng qua vt ch trung gian t c lin quan n tui ca vt ch nh: Chilodonella spp, Trichodina spp k sinh trn c cc giai on. Tuy nhin giai on c bt, c hng, c ging nui mt dy, c th cn non nn thng c cng v t l nhim cao v gy thit hi ln cho sn xut. Tnh n ca vt ch nh hng n k sinh trng: Tr s k sinh trng l ngoi k sinh v k sinh trng chui trc tip qua da vo k sinh bn trong c th vt ch ra cn li k sinh trng l ni k sinh chu tc ng rt ln n chui thc n ca c. Do tnh n khng ging nhau m chia cc loi c lm 2 nhm: c hin v c d. Chinnmnbhuc,thcvtthusinh,ngvtnhnnhaycmnhimksinh trngcchukphttrintrc tiphaygiunsncchukphttrinqua1vtchtrung gian l ng vt ph du v d: c hin hay nhim k sinh trng l bo t si Cnidosporidia, c trm c thng nhim k sinh trng Balantidium. Ngc li c d n cc ng vt thu sinh ln v n c, thng b nhim cc ging loi k sinh trng c chu k pht trin phc tp, giai on u trng ca k sinh trng k sinh cc vtchlvtmicacdnhcnheo,cthiuhaycmnhimsnlsongch Isoparorchis sp c tr, c vc...thng cm nhim sn l song ch Dollfustrema sp. Bnh hc thy sn 19C n sinh vt y hay b nhim cc loi giun sn m qu trnh pht trin ca chng c qua vt ch trung gian l nhuyn th, u trng cn trng... nh c chp thng b cm nhim sn dy Caryophyllaaeus sp. Tnh trng sc kho ca vt ch tc ng n k sinh trng: ng vt kho mnh sc khng tng khng d dng b nhim k sinh trng, ngc li ng vt gy yu sc khng gim, k sinh trng d dng xm nhp vo. V d: trong cc ao nui c nu nui dy, thc n thiu, mi trung nc bn c chm ln ddngphtsinhrabnhvthtrong qu trnhngnuichng, c ging nu khng thchinngquytrnhkthut,ccaongcmtdycddngbcmnhim trng bnh xe Trichodina hn ao c mt va phi v cho n y . 1.2.5.3. Quan h gia k sinh trng vi nhau: Trn cng mt vt ch ng thi tn ti mt ging h nhiu ging loi k sinh trng khc nhauvvygiachngsnysinhmiquanhtnghhayikhng.Ckhiksinh trngnytntiscchsphttrinksinhtrngkia,tmiquanhnylmnh hng n khu h k sinh trng. TheoE.G.Skruptrenko1967,khicbnhimksinhtrngApiosoma(Glossatella)th khng nhim k sinh trng Chilodonella v ngc li. Thng chng ta gp u trng ng vt nhuyn th 2 v k sinh trn mang c vi cng nhim cao th t gp sn l n ch v gip xc k sinh nguc li cng nh vy. Mt s ging loi k sinh trng tuy khc nhau nhng cng sng trn c th mt vt ch n c tc dngh tr nhau nn khi gp k sinh trng ny ng thi cng gp k sinh trng kia cngtntinh:gingksinhtrngTrichodinaviChilodonella,Ichthyophthirius; Lernaea vi Trichodina; Acanthocephala vi Azygia, Asymphylodora. 1.2.5.4. Tc dng ca iu kin mi trng i vi k sinh trng. K sinh trng sng k sinh trn c th vt ch nn n chu tc ng bi mi trng th nht l vt ch ng thi mi trng vt ch sng hoc trc tip hay gin tip cng c nh hng n k sinh trng, lm tc dng n mc tc hi ca k sinh trng i vi vt ch. muicathuvcnhhngnksinhtrng:Ccyuthohcnhhngrt lnnksinhtrngksinhtrnngvtthusntrongnglulmuica thu vc. mui trong cc thu vc nh hng n khu h ca c v khu h vt ch trung gian, vt ch cui cng ca k sinh trng. Gia cc ging loi c s mn cm gia k sinh trng c khcnhaunnkhikhuhcthayinhhngnkhuhksinhtrng.muicao lm nh hng n s pht trin ca vt ch trung gian, k sinh trng c nc ngt. Vt ch trung gian l ng vt nhuyn th, gip xc cn mi trng c nhiu mui Carbonate to v. mui nh hng n k sinh trng khng qua giai on c vt ch trung gian. Cc cht CloruavmuiSunfattrongncmnlmnhhngnksinhtrnglnguynsinh ng vt, sn l n ch, gip xc nhuyn th k sinh trn c nc ngt. Cc loi c di c trng, c con khi ra bin i b phn k sinh trng k sinh trn c thca n b tiu dit v ngc li c b m khi vo sng trng cng vy. Bi Quang T20nh hng ca nhit nc n k sinh trng: Nhit nc khng nhng nh hng trc tip n k sinh trng k sinh trn c th ng vt thu sn m cn nh hng n vt ch trung gian, vt ch cui cng v iu kin mi trung. Mi ging loi k sinh trng c thsng,phttrinnhitncthchng.Nhitqucaohayquthpukhng pht trin c v d: sn l n ch 16 mc Dactylogyrus vastator nhit 24-260C sau khi trng thnh 4-5 ngy s thnh thc v trng, 3-4 ngy phi pht trin t l n 80-90%, nhng sn l n ch 16 mc loi Dactylogyrus extensus thch hp nhit 15 0c, nunhitcaotlncatrngsrtthp.KsinhtrngTrichodinaphttrinmnh vo cui xun u ma h, nhit nc trn 30 0C cng v t l nhim ca c i vi ksinhtrngTrichodinagimrrt.KsinhtrngmneoLernaeathnggpksinh trn c vo ma v ng xun hoc u ma h khi nhit cao t bt gp chng k sinh. GiuntrnPhilometracarassiiksinhtrncmaxuntslngcaonhtnhngqua ma thu, ma h th tri li. cimcathuvcnhhng n k sinh trng:Thu vc t nhin, thu vc nui ngvtthusndocdintchsu,bokhcnhaunnnhhngnthnh phn s lng v cng nhim ca k sinh trng. Trong cc thu vc t nhin s loi k sinhtrngphongphhntrongccaonuicdokhuhc,khuhngvtlvtch trung gian, vt ch cui cng cng a dng hn, mt khc thu vc ao thng xuyn c ty dn, dit tp, tiu c, ng thi nui trong thi gian ngn. Tuy th tm, c nui trong ao mt dy c bn phn v cho n nn mi trng nc bn hn lm cho k sinh trng k sinh trn tm, c pht trin thun li v d ly lan nn ging loi t nhng cng v t l nhim ca k sinh trng trn tm, c cao hn cc thu vc mt nc ln. 2.Bnh l. 2.1. S pht sinh v pht trin ca bnh: 2.1.1. nh ngha c th sinh vt b bnh: C th sinh vt b bnh l hin tng ri lon trng thi sng bnh thng ca c th khi c nguynnhn gy bnh tc ng. Lc ny c th mt i s thng bng, kh nng thch nghi vimitrnggimvcbiuhintriuchngbnh.Lcquanstcthsinhvtcb bnh hay khng cn phi xem xt iu kin mi trng chng hn ma ng trong mt s thuvcnhiththpcnmyny haynnpniknkhng btmilhin tngbnhthng,cnccmakhcthititmpckhngnltriuchngbbnh. Hay nh ngha mt cch khc bnh l s phn ng ca c th sinh vt vi s bin i xu ca mi trng ngoi cnh, c th no thch nghi th tn ti, khng thch nghi th mc bnh v cht. ng vt thu sn b bnh do nhiu nguyn nhn ca mi trng gy ra v s phn ng ca c th c, cc yu t ny tc dng tng h ln nhau di iu kin nht nh. 2.1.2. Nguyn nhn v iu kin pht sinh ra bnh. Nm vng nguyn nhn v iu kin pht sinh bnh hiu r bn cht ca bnh v c bin php phng tr bnh c hiu qu. 2.1.2.1. Nguyn nhn. Tc dng kch thch gy bnh cho c th sinh vt: C th sinh vt sng trong mi trng chu tc ng v s kch thch, a s cc yu t ny khng c hi li rt cn duy tr s sngchosinhvtnhnhitnc,pH,xy,...nhngdotcngbicngqu Bnh hc thy sn 21mnh, thi gian qu di hoc yu t khng c li vi bn thn sinh vt. Cc kch thch v c gii, kch thch vt l, kch thch ho hc v cc kch thch do sinh vt gy ra. Nguyn nhn gy bnh d dng thy, ph bin nht gy tc hi mnh m l yu t sinh vt (mm bnh). Sinh vt tc ng n c, tm di hnh thc k sinh cc t bo t chc c quan gy bnh cho c, tm. Yu t sinh vt c th tc ng trc tip n c, tm. Sinh vt c th tc ng gin tip n mi trng ca c, tm ri t c th nh hng n hot ngsinhlbnhthngcac,tmnhmtsloitoMicrocystis,Gymnodiniumgy c cho c, tm. Do thiu cc cht c th cn: Trong qu trnh sng c th v mi trng c s lin h mt thit, c tc dng qua li, cc cht c th cn khng c hoc khng lm cho c th bin i thm ch c th cht nh bnh thiu dinh dng. Cn c vo mc c th chia lm 2 loi: -Dokhngchocthiuccchtrtcnduytrcthsng,cthc,tmscs bin i rt nhanh chng thm ch c th lm cho c, tm cht t ngt nh oxy, nhit nc... - Do thiu mt s cht hoc do iu kin sng lc u c th sinh vt cha c bin i r nhng c ko di lin tc th s lm cho qu trnh trao i cht b tr ngi, hot ng ca cchmenbriloncthkhngphttrincvphtsinhrabnhnhthiucht m,m,ng,vitamin,chtkhong.vv...Nutrongthcncac,tmthiuCanxiv Photpho th lm cho c, tm b bnh ci xng, cong thn, d hnh, mm v,..., ngoi ra cn nh hng n men tiu ho. Do bn thn c th sinh vt c s thay i dn n b bnh: C mt s cht v mt s tc dng kch thch trong iu kin bnh thng l yu t cn thit p ng nhu cu c th pht trin bnh thng nhng do c th sinh vt c s thay i hoc mt s t chc c quan c bnh l cc yu t tr thnh nguyn nhn gy bnh. 2.1.2.2. iu kin pht sinh bnh. Cthsinhvtphtsinhrabnhkhngnhngchdonguynnhnnhtnhmcnc iu kin thch hp. Do iu kin khc nhau m nguyn nhn gy bnh c lm cho c th sinh vt pht sinh ra bnh hay khng. iu kin gy bnh bao gm bn thn c th sinh vt v iu kin mi trng. C th sinh vt nh tui, tnh trng sc kho, c ci...qua theo di trong mt ao nui c tht c nhiu loi c nhng loi gip xc Sinergasilus polycolpus Yin 1956ksinhtrnmangcm,ctrmliukinksinhtrngSinergasiluspolycolpus gy bnh. K sinh trng m neoLernaea polycolpus Yu 1938 k sinh trn da, trn ming c m, Lernaea ctenopharyngodontis Yin 1960 k sinh trn da c trm c u b nhimnh vy, c u trng ca ging Lernaea tn ti nhng khng c i tng c thch hp nh c m hoc c trm th bnh khng xy ra. iukinmitrngnhkhhu,chtnctnhhnhnuidngkhuhsinhvtnh hng n nguyn nhn gy bnh. Phn ln cc bnh vi sinh vt pht trin mnh trong iu kin mi trng nui c, tm b nhim, cc bnh do nguyn sinh ng vt gy ra thng ao ng nui c, tm mt qu dy, thc n khng y , mc nc qu thp. Cc loi sn l song ch pht trin v k sinh trn c phi nh c vt ch trung gian l c Limnae v vt ch sau cng l chim. Qua cc v d trn chng t c hay sinh vt thu sn khc b bnh u c nguyn nhn nht nh nhng n khng phi tc dng c lp m di iu kin bn ngoi v bn trong ca c thphthuytcdng.Nguynnhnquytnhqutrnhphtsinhvctnhcbn Bi Quang T22ca bnh cn iu kin ch c tc dng lm tng ln hay cn tr cho qu trnh pht sinh pht trin ca bnh, iu kin nh hng n nguyn nhn. Nguyn nhn v iu kin khi nim ny cng ch tng i c khi cng mt nhn t nhng lc ny l nguyn nhn lc khc l iu kin v d khng thc n c, tm cht i hoc c lc thc n thiu c, tm b i. 2.1.3. Cc loi bnh: 2.1.3.1. Cn c nguyn nhn gy bnh phn chia cc loi bnh: Bnh do sinh vt gy ra: - Bnh k sinh: Ch nhng bnh do sinh vt k sinh gy ra: + Bnh vi sinh vt do virus, vi khun, nm, to n bo gy ra. + Bnh k sinh trng do nguyn sinh ng vt, giun sn, a c, nhuyn th, gip xc gy ra. - Bnh phi k sinh: c, tm b bnh do sinh vt gy ra nhng khng phi di hnh thc k sinh, thng do to loi gy c cho c, tm, thc vt, ng vt hi c. Bnh do phi sinh vt:Bnh gy ra cho c, tm khng phi do sinh vt tc ng. - Do cc yu t c hc, ho hc, vt l tc ng. - Do s tc ng bi thiu cc cht v iu kin m c th c cn nh cc cht dinh dng khng , s lng thc n thiu... 2.1.3.2. Cn c tnh hnh nhim ca bnh chia. - Nhim n thun: C, tm b bnh do mt s ging loi sinh vt gy bnh xm nhp vo c th gy ra. - Nhim hn hp: C, tm b bnh do cng mt lc ng thi 2 hoc nhiu ging loi sinh vt xm nhp vo c th gy ra. - Nhim u tin: Sinh vt gy bnh xm nhp vo c th c, tm kho mnh lm pht sinh ra bnh. - Nhim tip tc: C, tm b nhim bnh trn c s c nhim u tin nh c b nhim nm thu my sau khi c th c b thng. - Nhim ti pht: C, tm b bnh khi nhng khng min dch, ln th 2 sinh vt gy bnh xm nhp vo lm cho c pht sinh ra bnh. - Nhim lp li: C th c, tm b bnh khi nhng nguyn nhn gy bnh vn cn, tm thi trng thi cn bng gia vt ch v vt k sinh nu c sinh vt gy bnh cng chng loi xm nhp vo hoc sc khng ca c th yu s nhim. 2.1.3.3. Cn c vo triu chng ca bnh chia: - B bnh tng b phn (cc b).: Bnh xy ra c quan no th qu trnh bin i bnh l chyuxyra,cthnggpnhbnhngoida,bnhmang,bnhngrut, bnh ngoi c v bnh mt s c quan ni tng... - B bnh ton thn: Khi c, tm b bnh nh hng ti ton b c th nh c, tm b bnh trng c, b i , b thiu cht dinh dng. S phn chia trn ch l tng i bt k bnh no thng khng th ch nh hng cc b cho 1 c quan m phi c phn ng ca c th. Bnh ton thn bt u biu hin tng b phn v pht trin ra dn ton b c th. 2.1.3.4. Cn c vo tnh cht qu trnh ca bnh chia: - Bnh cp tnh: Bnh cp tnh c qu trnh pht trin rt nhanh chng ch trong vng my ngyn1-2tun.Cthbbnhhotngsinhlbnhthngbininhanhchng Bnh hc thy sn 23thnh bnh l, c mt s bnh triu chng bnh cha kp xut hin r trn c th cht. V d nh bnh trng bnh xe mang c ging ch trong 24-48 gi c cht ht; bnh nm mang cp tnh ch cn 1- 3 ngy c cht; bnh xut huyt do Reovirus c trm c, c b bnh sau 3-5 c th cht ti 60-70%; bnh pht sng ca u trng tm khi pht bnh ch cn 1-2 ngy tm cht ht; bnh m trng gip xc sau khi pht bnh t 3-10 ngy gip xc trong ao nui cht hu ht. - Bnh th cp tnh: Qu trnh pht trin ca bnh tng i di t 2-6 tun, triu chng ch yucabnhxuthinvphttrinnhbnhnmmangcptnh,tchcmangbph hoi, mang b sng l lot, t mang b t; bnh m c do vi khun. - Bnh mn tnh: Qu trnh pht trin ca bnh ko di c khi hng thng hoc hng nm. Nguyn nhn v iu kin gy bnh tc dng trong thi gian di v khng mnh lit nhng cng khng d dng tiu tr. V d nh bnh nm mang mn tnh ca c bin i v bnh l rtnhchmtstbomangbcht,mangtrngra.BnhMBV(Penaeusmondon Baculovirus) nhim tt c cc giai on ca tm s, khng gy tm cht t nhng lm cho tm chm ln v t l cht dn tch ti 70%. Trong thc t ranh gii gia 3 loi khng r v gia chng cn c thi k qu v tu iu kin thay i n c th chuyn t dng ny sang dng khc. 2.1.3.5. Cc thi k pht trin ca bnh: Di tc dng ca cc yu t gy bnh, c th sinh vt khng phi lp tc b bnh m n phi tri qua mt qu trnh. Cn c vo c trng pht trin tng giai on ca bnh m chia lm my thi k: Thi k bnh: L thi k t khi nguyn nhn gy bnh xm nhp vo c th n lc xut hin triu chng bnh u tin, lc ny hot ng sinh l bnh thng ca c btu thay i. Thi k ny di hay ngn khng ging nhau c khi ch my pht nh hin tng trng cckhivangynhccbnhtruynnhim,ckhilimythng,mynmnhcc bnh k sinh trng. do n ph thuc vo chng loi, s lng, phng thc cm nhim ca yu t gy bnh cng nh sc khng ca vt ch v iu kin ca mi trng. C th c, tm b thng khng c thi k bnh. Thi k bnh chia ra lm 2 giai on: - T khi tc nhn gy bnh xm nhp vo c th n sinh sn, l i vi cc bnh do sinh vt k sinh gy ra. - T khi sinh sn n lc b bnh u tin. Thi k bnh sinh vt k sinh tm mi cch tch lu cht dinh dng tng cung cng sinhsnvhotngcan.Vvtchtrongthiknytoranhngyutmin dchphngv.Thikbnhnuc,tmcchmscchony,mitrng sng sch s th thi k ny ko di tc hi n c, tmhu nh khng ng k. Cn theo ditrongqutrnhngnuic,tmphthinsmvcbinphpphngtrkp thi trong giai on ny l tt nht. Thi k d pht: L thi k chuyn tip t lc xut hin du hiu bnh l u tin n lc bnhlrrng.Thiknytcnhngybnhtcngntchccquancac, tm. Vi tc nhn gy bnh l sinh vt thi k ny chng sinh sn cng mnh . Thi k d pht thng ngn c mt s bnh triu chng khng th hin r nh bnh xut huyt mang. Thi k pht trin: L thi k bnh pht trin cao nht, triu chng in hnh ca bnh th hin r. Qu trnh trao i cht cng nh hnh thi cu to ca t bo t chc cc c quan trong c th c, tm c s bin i. Thi k ny nng nht v thng gy tc gi ln cho c, tm. Trong thc t phn chia rnh rt 3 thi k nh trn l rt kh, bi n chu nhiu yu t nh hng v trong qu trnh tin trin ca bnh thay i phc tp. Bi Quang T24 Thi k pht trin ca bnh do tc ng ca nhiu yu t nh:nguyn nhn v iu kin gy ra bnh, sc khng ca c, tm v con ngi p dng cc bin php phng tr kt qu bnh c th chuyn sang cc kt qu sau: - Bnh ca c, tm c cha khi c th hon khi phc: C, tm b bnh vo thi k pht trin nhng nu p dng kp thi cc bin php phng tr kt hp vi cc quy trnh k thut ng nui th tc nhn gy bnh b tiu dit, sau mt thi gian cc du hiu bnh l dn dn mt i, c, tm dn dn tr li hot ng bnh thng, hin tng c, tm cht do b bnh trongthuvccchmdt.Trongthiknycnquantmchoc,tmncht lng sc kho ca c, tm c phc hi nhanh chng m bo cho c, tm sinh trng bnh thng. - Cha hon ton hi phc: Tc nhn gy bnh cho c, tm b tiu dit nhng cha tht trit mt phn cn tn ti trong mi trng nc hoc y ao. Thi k ny c, tm cht gimirtnhiuscthcnsngduhiubnhltrncthmtdn,cchotng cac,tmtrlibnhthng.Tuyvyc,tmrtddngnhimbnhtrlinuiu kin thun li nh sc khng ca c, tm gim. - Khng th cha khi bnh: C th c, tm b tc nhn gy bnh xm nhp lm cho nhiu tchccquanbhuhoi,sckhngcacthc,tmgimdntronglctc nhngybnhliphttrinmnhsaumtthigiangy tchilnnc,tm.Thi gian ny hot ng sinh l bnh thng ca c, tm khng th hi phc, c ,tm s cht t ngt hoc cht dn dn v d khi p trng c chp, phi pht trin n giai on hnh thnh bcmtnhngnunmthumybmvomngtrng,tonbstrngspnbcm nhim b ung ht. 2.2. Qu trnh c bn ca bnh l: Khi tc nhn gy bnh xm nhp vo c thgy ri lon s hot ng bnh thng ca cc c quan, hin tng ri lon y gi l hin tng bnh l, nhiu bnh c cng 1 qu trnh bnh l th gi l qu trnh c bn ca bnh l. 2.2.1. Gy ri lon s hot ng 1 phn ca h thng tun hon: Cthmunduytrssngcncbmytunhonkhomnh.Hthngtunhon khng nhng cung cp cht dinh dng cho c th v thi cc cht cn b ra ngoi m khi c th b bnh cn tp trung bch cu v khng th chng li tc nhn gy bnh. Do c th b bnh, h thng tun hon b ri lon qu trnh trao i cht ca t bo t chc b tr ngi, sc khng s yu thm ch c th lm cho c, tm b cht. Sriloncahthngtunhonchiaralm2loi:Rilonccbhocrilonton thn. S ri lon 1 phn b my tun hon ch xy ra b phn c bit ca c th nhng b phn khc khng nhn thy r. Ri lon ton b b my tun hon l lc chc nng ca b my tun hon km tc dng. tchbit s ri lon cc b v ton phn ca h thng tun hon ch l tng i bi v s ri lon 1 phn h thng tun hon l biu hin cc b ca s ri lon ton thn mt khc lc u cc c quan trong tim, no pht sinh ri lon cc b c th tin ti pht trin ri lon c h thng tun hon do c 2 loi ri lon c quan h mt thit vi nhau lc u bao gi cng bt u t ri lon cc b. 2.2.1.1. T mu: Bt k mt t chc hay mt c quan no ca c th c hm lng mu vt qu s lng bnhthngthgiltmu.Hintngldoccmaoqun,ngmchnh,tnh Bnh hc thy sn 25mch nh n ra qu nhiu v cha y mu. Do ngun gc mu a n m chia ra t mu ng mch v t mu tnh mch. T mu ng mch: Mu t ng mch ln i vo cc t chc c quan vt qua s lng bnh thng dn n t mu ng mch. C hin tng ny do phn x lm cho ng mch nhnra,slngmaoqunhotngcngtngln,muchynhanh,trongmuc nhiuoxy,quatrnhtraoichtcatbotchctngnhanhdoccbtchcb sng c mu ti, nhit tng ln b nng, c, tm hin tng ny khng r. T mu ng mch khng phi lc no cng bnh l nh lc n trong ng tiu ho c t mu l hin tng trong qu trnh hot ng sng ca c th sinh vt. Kt qu ca t mu ng mch quyt nh bi v tr v qu trnh pht trin, nu t mu qu trnh trao i cht nh t bin tr bnh, vim lot t mu l phn ng phng v ca c th. T mu ng mch nghim trng l lm cho lng mu b phn kh gim t ngt gy ra nh hng xu, c lc xy ra chy mu khng v cng nguy him n tnh mng. T mu mn tnh c th lm cho vch mch mu ca c th dy hn, thi gian t mu ca t chc khng ko di th mc nh hng khng nguy him. Tmutnhmch:Musaukhitinhnhtraoichtchyvtnhmchlnqut mu tch t li trong cc mao qun v tnh mch nh qu nhiu th gi l t mu tnh mch, khi tnh mch t mu, mu chy chm, qu trnh trao i cht b ri lon, nhit h thp, xy trong mu gim, c nng hot ng ca cc t chc c quan yu. Sau khi t mu tnh mch tnh thm thu ca vch mch mu tng ln lm pht sinh ra hin tng ph v tch nc trong t chc. Nguyn nhn ch yu dn n t mu tnh mch l do mu tr ra b tr ngi,cthvtnhmchbnn,mchmubtc.Nutmutnhmchnng,trong mu c nhiu cht c c khi cn thiu xy v , thiu cht dinh dng lm cho chc nng hot ng ca cc c quan b ri lon. 2.2.1.2. Thiu mu: Lc lng mu ca c th gim hoc s lng hng huyt cu t i so vi bnh thng gy ra hin tng thiu mu, mt c quan hay t chc no ca c th b thiu mu th gi l thiu mu cc b. B phn thiu mu nhit h thp, mu sc bin nht. T chc b thiu mu lc u th tch nh li nhng v sau do thiu dinh dng sn sinh ra hin tng phn gii lm cho t chc b ph, th tch tng ln nh bnh nm mang lm cho mang thiu mu t chc mang mu trng nht, mt s b phn sng phng ln. Nguyn nhn dn n hin tngthiumucthdosinhvthtmu,dotcmchmu,dodttcabmytun honhocthnhphntomunh:Fe,Ca,P...khng.Tchicavicthiumucn tuthucvomcthiumu,thigian,tnhmncmcatchc.Nuthiumu nghim trng c th lm cho t bo t chc b cht dn dn, lm t lit ton thn. 2.2.1.3. Chy mu (xut huyt): Chymulhintngmuchyrangoihuytqun,numuchyrangoicthth gilchymungoicnmutchtlitrongthxoangcacththgilchymu trong, c khi c chy mu trong ln chy mu ngoi. Chy mu c th do vch mch mu b ph hoi cng c th vch mch mu khng b dp nt nhng do tnh thm thu ca vch mch mu tng ln m mu c th thng qua c v d rn c Argulus k sinh bm trn mang v da lm chy mu. Cc nguyn nhn gy ra chy mu gm nhiu yu t nh c hc, vt l, ho hc v sinh vt tc dng. Chy mu cp tnh lm mt s lng mu tng i ln hoc cc c quan trong yu b chy mu thng dn n hu qu xu kh tr khi. 2.2.1.4. ng mu: ng mu l hin tng mt s thnh phn ca mu trong tim hay trong mch mu dnh li b ngng kt thnh khi. Nguyn nhn lm ng mu l lc vch mch mu b thay i do Bi Quang T26btnthng,vchgghdlm cho huyt tiu bn lng ng ng thi mch mu sau khi b tn thng tng t bo thng b c kh nng sn sinh ra cc si keo lm cho huyt bn dnh li, sau s nhanh chng phn gii to ra nhiu men ln men lin kt cng vi Ca trong mu lm cho Thrombinnogen bin thnh Thrombin. Muchychmtoiukinthigianchomuvangdnhtrnvchmchmuth FibringenchuynthnhFibrinbnvnglmchomungngkt.Muchychmhoc ngng kt, huyt tiu bn c iu kin tch ra 2 bn vch mch mu v tip n vi mng trong ca mch mu lm tng kh nng dnh kt v lng ng, mu chy chm cn gip cho men ngng kt v cc nhn t ngng kt mu hot ng d dng hn, ngoi ra cn c th do tnh cht ca mu thay i dn n ng mu. Banguynnhntrnngthitntinhngsphnngcacth,trngthicah thngthnkinhcnghatrongshnhthnhngmu.ngmulmtcmchmu gy ri lon hot ng ca h thng tun hon. 2.2.1.5. Tc mch mu: Mukhngchycncctchccquan,do1tcngtnthng,gitmxm nhp vo c mch mu di chuyn theo mu gy tc mch mu. - Do vch mch mu b tn thng gii phng Protrombokinaza l mm mng ng mu. Protrombokinaza Thrombokinaza Ca++Fibrrinogen ProthrombinThrombin Fibrrin bn vng - Do sinh vt, u trng, trng, trng trng thnh ca k sinh trng lm tc mch mu nh sn l song ch Sanguinicola sp k sinh trong mu c, nm mang k sinh trn mang. - Do bt kh: 1 s kh hm lng ho tan trong nc qu cao n tn ti di dng bt kh nh to ra s chnh lch v p sut bn trong v ngoi mch mu, bt kh thm thu vo mch mu gy tc mch mu nh nh bt kh O2. - Tc mch do u bu: T bo u bu c tnh c kh nng i vo t chc vo h thng tun hon n mch mu, cc mch lm ba dn n tc mch. 2.2.1.6. S thay i thnh phn ca mu: Mu gm c huyt tng v cc thnh phn hu hnh trong huyt tng l hng cu, bch cu, tiu cu. T bo bch cu c 5 dng: T bo bch cu Limpho, t bo bch cu mono, t bo bch cu trung tnh (Neutrophin), t bo bch cu a acid, t bo bch cu a kim, ttc5dngtbobchcuukhctbohngcukhngchaHemoglobinvvy khng c mu. Bch cu c th vn chuyn ngc dng mu xuyn qua vch mch mu i vo cc m, c kh nng di chuyn dng amp. S lng hng cu, bch cu thay i ph thucvotrngthibnhl,tnhtrngsckho,giaionphttrin,phtdccami loi c, tmng thi cn ph thuc vo tc nhn gy bnh. Khi c, tm nhim bnh thnh phn v s lng bch cu thay i, s lng bch cu trung tnh v t bo bch cumomo tnglnnhngtbobchculimphobgimxungbivtbotrungtnhvtbo mono c chc nng tiu dit vi khun. Nguyn nhn lm cho bch cu tp trung l do nhng cht ho hc v c t ca sinh vt tit ra. Bnh hc thy sn 27Theo O.N.Bauer 1977 khi c b bnh nm mang t bo bch cu lympho bnh thng l95-99% khi c bt u b bnh t bo lympho gim xung 64-75%, t bo mono bnh thng 0,5%, c bt u b bnh ln 2-3%, bch cu trung tnh 0-2,5% c kho tng ln 8-24% c bnh. Theo A.I.Mikoian c kho bch cu trung tnh l 0,2%, c b bnh m dng mn tnh bch cu trung tnh 1,5%, c b bnh m dng cp tnh tng ln 5-8%. Mt s c th c b bnh do k sinh trng k sinh, ngi ta quan st thy lng bch cu a acid tng ln chng t dng bch cu ny ng vai trno chng li tc hi ca k sinh trng. 2.2.1.7. Hoi t cc b: Hoitccblmtbphnno ca c th do cung cp mu b nh tr lm cho t chc b hoi t. Nguyn nhn thng gp l do xoang ng mch b tc, ngoi ra cn cthdosnnbnngoingmch.Btkngmchnobtckhngchldo nhn t c hc lm cn tr mu chy m ng thi h thng thn kinh b kch thch mnh lm cho mch mu b co git lin tc cng dn n hoi t b phn. 2.2.1.8. Ph v tch nc: Dchthctchttrongcckhecacctchcvislngnhiuthgilphcn dch th tch tc trong xoang th gi l tch nc. Trong dch th ny hm lng albumin gim, trong c th hay ra ngoi c th u khng lin kt, dch trong c mu xanh vng. Thtchcccquantchcbphtnglnbmtbnglongxanhxao,cnnghot ng ca cc c quan b gim st. Nguyn nhn dn n cc t chc c quan b ph v tch nc rt nhiu: C th t chc b chn p, do tc ng c gii, c th sinh vt b i hoc thnh phn dinh dng trong khu phnthnthiu,ganbxcng,thnbyu,hthngthnkinhbrilonhocdok sinh trng xm nhp vo c th. Nhn trung cc t chc c quan b ph v tch nc sau khi tiu tr c nguyn nhn gy bnh c th hon ton hi phc. Nu thi gian qu di, cc t chc c quan b ph v tch nc c nhng bin i qu ln nn mc d nguyn nhn gy bnh tiu tr nhng hin tng ph v tch nc vn cn lm cho t chc b vim, chc nng hot ng ca t chc vn b ri lon, mt s c quan trng nh no chng hn b ph v tch nc d dng lm cho c quan vt ch b t vong. 2.2.2. Trao i cht b ri lon. Btkmttchcnolcnghcngnhlchotnguthchinqutrnhtraoi cht. Lc c th hot ng mnh, qu trnh trao i cht tng ln v ngc li lc ngh ngi qutrnhtraoichtgimxung.Qutrnhtraoichtchusiutitcahthn kinhtrungng.Trongqutrnhccchtthamgiatraoiclinquanmtthitvi nhau, lc c th b bnh s hot ngtrao i cht v s lng v cht lng u pht sinh ra bin i. tin li nn tch ring tho lun tng phn trong qu trnh trao i cht b ri lon nh hng n s bin i ca t bo t chc. 2.2.2.1. Lm cho t chc teo nh li. Qutrnhtraoichtbrilonlmchothtchcatchc,cquancacthpht trin bnh thng nh li th gi l t chc b teo c. T chc, c quan teo nh c th do th tch t bo nh li hoc s lng t bo gim, hai qu trnh ng thi pht sinh hoc xy ra trc sau. T chc c quan teo nh khng phi tt c u b bnh ch khi no qu trnh trao i cht b ri lon c th mi mc bnh. Bi Quang T28Nguyn nhn lm cho t chc bteo nh: - Do h thng thn kinh b bnh lm cho qu trnh trao i cht b ri lon nn t chc, c quan teo nh. - Do b chn p, nn lu ngy lm cho h thng tun hon b phn b ri lon dn n t chc c quan b teo nh nh u trng sn dy Ligula k sinh trong rut c chp, c dic lm cho m c, tuyn sinh dc v mt s c quan bn trong c teo nh. - S hot ng ca mt s tuyn ni tit mt kh nng iu tit lm cho t chc c quan teo nh.Disiutitcahthng thn kinh trung ng, cc tuyn ni tit trc tip iu tit qu trnh trao i cht do lc chc nng hot ng ca tuyn ni tit b ri lon lm chotchccthbteonhnhchnngnosuyyucthlmchotuyngiptrng, tuyn thng thn teo nh. - Tc dng ho hc hay vt l cng lm cho c quan teo nh nh cc cht phng x.. - Mt s c quan sau mt thi gian di khng hot ng c th b teo nh. - Ton b c th sinh vt teo nh c khi do b i hoc do h thng tiu ho b tc, c th thiu dinh dng dn n c th gy g ni tng teo li, teo nh biu hin trc tin l t chc m n m, c tim, l lch, gan sau cng l no. 2.2.2.2. Bin i v s lng v cht t bo, t chc: Qu trnh trao i cht b ri lon lm cho s lng v cht lng t bo v cc cht m ca t bo thay i so vi bnh thng gi l bin i tnh cht. C my dng bin i di y: T bo, t chc c quan sng ty: Thng do bnh truyn nhim cp tnh, trng c, thiu oxy ton thn dn n lm cho t bo t chc sng ty. Lc ny t bo tin hnh thu phn ngthicsbiniion,hmlng ion K+ trong t bo gim, hm lng Na+ v hp cht Clorua tng, s thay i gia cc thnh phn ion l do t bo b tn thng khng nng lng hot ng. Bininc:Trongdchtngvhchtbocnhiukhngbo,loikhngbony khng cha m, ng n v nim dch hoc ch c rt t Protein lng ng, s xut hin ca khng bo lm t bo tch nc. S bin i nc v sng ty ca t bo c quan h mt thit vi nhau n lm cho t bo tn thng nhanh lc ion K+ trong mu gim, trong t bo ion K+ ra ngoi t bo, ion Na+ ca dch t bo vo trong t bo. Lc c th b chong (xc)tbothiuoxy,nnglngtbosnrakhnglmyukhnngdnionNa+ nn ion Na+ i vo t bo m ion K+ ra ngoi t bo, di cc tnh hung u lm cho ion Na+ trong t bo tng nhiu ln dn n t bo trng nc tc l bin i nc. Bin i trong sut: Bin i trong sut l ch dch t bo hoc cht m ca t bo xut hin cc cht ng u trong nh thu tinh. Cc cht ny nhum bng dung dch Eosin bt mungu,ngitagitbobinidngtrongsutthutinh.Sbininy thng xy ra trong t bo t chc m, t bo t chc mu. M bin i: Trong dch t bo xut hin cc git m, ngoi ra lng m vt qu phm vi bnh thng hoc bn thn t bo vn khng c git m nhng trong dch tng t bo c xut hin git m th ngi ta gi t bo t chc bin m. C quan bin m nghim trng lmchothtchtng,mkhngrnchcmuvngkhngbnhthng.Mbini thng l bnh do qu trnh oxy ho cc cht hu c khng m bo do nguyn nhn thi mu gy ra ngoi ra c th do mt s cht c, do c t vi khun lm cho t bo t chc bin i m. Traoikhongbrilon:CcchtkhongCa,Fe,K,Mg,Na...ulccchtdinh dungquantrngcangvt,qutrnhtraoichtkhongbrilonlmchohot Bnh hc thy sn 29ng bnh thng ca c, tm tr thnh bnh l. Trao i Ca b ri lon thng gp hn c mui Canxi theo thc n vo rut c hp th tri qua mt qu trnh bin i, trong mu v dich th kt hp vi protein. C th trng thi bnh thng Ca tch trong xng, rng l ch yu, hm lng Ca trong c th thng n nh nu tha bi tit ra mi trng qua rut v thn. Nhng lc thn kinh mt kh nng iu tit, tuyn ni tit b ri lon hoc c bnh vim thn mn tnh, h xngbbnh th trong xng sn c hin tng lng ong . Nu Canxi ho trong vch mch mu c th lm cho vch mch mu mt kh nng n hi, lm bin i tnh cht v mch mu d b v. 2.2.3. T chc c th sinh vt b vim. Chng vim l hin tng c th sinh vt phn ng phng v cc b hay ton thn khi c tc dng kch thch t ngoi vo thng qua phn x ca h thng thn kinh. y l qu trnh c bn trong qu trnh bnh l. 2.2.3.1. Bin i v bnh l ca chng vim. Bin i v cht ca t bo t chc: T chc trong vng b vim, t bo phn gii tch ra, lc mi c chng vim bin i v cht chim u th nht l chnh gia vim, cn xung quanh bin i v cht khng r rng. Nguyn nhn lm cho t chc c quan b vim l qu trnh trao i cht b ri lon, cht dinh dng thiu, ngoi ra cn do kch thch cc b. Mt khclctchccquancchngvimhthngtunhonrilon,tbotchcpht sinh ra bin i hoc hoi t pht trin ng thi c cc sn vt phn gii nh protein, acid hu c... lm cho tnh thm thu ca vch mch mu tng ln cng lm cho h thng tun hon ri lon. Thmthutbovccchtarangoi:Thmthuralhintngcthlcc chng vim, dch th v thnh phn t bo mu thm thu i ra khi mch mu vo t chc. Tchccthbvimtrchtmchmuthayi,dokchngkchthchngmch nh co li, thi gian rt ngn ng mch nh li n ra, cc mao qun trong vng vim cng n ra, lc u mu chy nhanh v sau mu chy chm li hng cu cha y xoang mch mu, thm ch c b phn mu ngng chy. Tnh thm thu ca vch mch mu cng tng ln, nu b tn thng nh cc phn t b thm thu ra cn b thng nng cc phn t ln nh globulin ri n hng cu v Fibrinogen cng thm thu ra. Trong dich th thm thu rac t bo b ng i ra nh hng cu nhng tri li c mt s t bo ch ng i ra nh bch cu. T bo bch cu xuyn ra khi mch mu sau khi tip xc vi vt kch thch, cc sn vt phn gii ca t chc, em bao li v c men thc hin tiu ho, y l hin tng thc bo. c t bo bch cu hin tng thc bo c xy ra hay khng kin cha thng nht. Tng sinh t bo: C th sinh vt khi c tc nhn kch thchgy bnh xm nhp pht sinh ra chng vim c th c pht ng li phng v nn mt s t chc nh mch mu, t bo mng li ni b, t bo si, t bo chc nh t bo gan sn sinh tng sinh t bo, vi mc ch cung cp b sung cho nhng t bo b thm thu ra ngoi lm cho t chc b vim khng pht trin thm ng thi phc hi nhanh chng cc tn tht ca t chc. Bt k mt chng vim no ca c th sinh vt n cng khng xy ra cc hin tng n c m n c quan h h tr mt thit gia 3 qu trnh bin i v cht lng, thm thu ra v tng sinh nhchnhgiakhuvcbvimbinivchtlngcthkchthchtbotchc xung quanh tng sinh, t botin hnh tng sinh mch mu nhn cc cht dinh dng thc y qu trnh bin i. Tng sinh t bo c th l ngun cung cp t bo v khng th thm thu ra. Trong qu trnh thm thu trao i cht ca h thng tun hon b ri lon nh hngnchtlngvslngtbotngsinh.Trongccchngvimcatchcc quan trn c th sinh vt, cng ca 3 qu trnh thng khng ging nhau, qu trnh bin i v cht chim u th. c, tm qu trnh thm thu ra tng i thp. Bi Quang T302.2.3.2. Triu chng chyu ca chng vim. - T chc c mu : T chc b vim sn sinh ra cc thnh phn ho hc v thn kinh cm gic c phn xnn c qu trnh t mu. Ngoi ra vng b vim trao i cht c tng ln, traoimbtrngi,kimvacidmtthngbng,acidcnngcaoddnn trng c cng c th lm cho mch mu n ra v vy khng nhng ch do t mu m cn do hng huyt cu thm thu ra. - T chc sng: Do dch th thm thu ra, do vi khun v cc sn vt trao i cht phn gii ra nhiu phn t nh, p sut thm thu tng, t chc b vim d dng sng to. - T chc b nng: Nhit bn trong c th cao hn bn ngoi, mu t bn trong chy ra ngoi nn vng vim c cm gic nng, c, tm ng vt mu lnh nn nhit bn ngoi v trong c th chnh lch khon 20C v vy khng c hin tng nng t chc b vim. - T chc vng vim b au: C ch au vng vim ca t chc kh phc tp, cc cht thm thu ra c sn vt lm au, ngoi ra cn c th do b nn. i vi c, tm cm gic ny kh bit c. - C nng ca t chc c quan b thay i: T chc c chng vim cng v nng lc cogincacgim,nimmcphntitranhiunimdchnhnglcnghimtrngli ngng phn tit nim dch. Cc c quan ni tng b vim khng c mt s triu chng nh nng,auvvnitngnhitcao,thnkinhcmgicthiu.Vimccbckhi cng c triu chng ton thn nh pht nng, bch cu tng. 2.2.3.3. Kt qu ca chng vim. Chng vim c th gy ra cho c th sinh vt hu qu nghim trng nhng y l mt phn ng phng v c th. Thng qua phn ng tiu tr nguyn nhn gy bnh, phc hi tn tht do bnh gy ra nh thm thu ra thnh phn dch th trong mu v bch huyt cu, lm sch nhng t bo cht, cc cht d dng, lm long nhng sn vt c hi. Tuy vy cc chtthmthurastrthnhmitrngnuidngvikhun,ccchtphngiirac victhdochngvimphttrinnmt trnh nht nh ngha tch cc b tc dng c hi trit tiu, c th sinh vt lnh hu qu khng tt. Kt qu sau cng ca chng vim trn t chc c th sinh vt: - Tuyt i b phn chng vim ca c th sinh vt kt thc tt nht l vim cp tnh, sau mtthigianngncththngquahpth,tisinhlinlivcnngcacthhon ton hi phc. -Trongqutrnhdinbincachngvim,tbochcbphhoiqunng,lctub khng th hi phc kt cu ban u phi thay th bng mt t chc mi do t bo si v sn sinh hoc nhng cht thm thu ra khng b hp th ht v thi ra ngoi m sau khi bin i hnh thnh cht si dnh li. Lc ny chng vim nh ch lu li l trng thi bnh l. Cc t chc c quan c nng c gim nhng mc c khc nhau. 2.2.4. Tu b, ph, tng sinh. 2.2.4.1. Tu b ca t chc c quan: T bo t chc ca c th sinh vt sau khi b hu hoi tin hnh hi phc li, qu trnh gi l tu b. C s sinh vt hc ca tu b l ti sinh ca cc t bo t chc. Nng lc ti sinhcacctbotchcphthucvochngloi,giaionphtdc,tnhhnhsc kho ca c th sinh vt ngoi ra cn s cung cp mu v cht dinh dng ca t chc. - H thng pht sinh nh hng n ti sinh: ng vt c h thng pht sinh cng thp nng lc ti sinh cng cao v ngc li nh ng vt thu tc ch cn gi li 1/4 c th cng c th hi phc li 1 c th hon chnh nhng ng vt c v ch mt 1 ngn chn cng kh hi phc li. Nh vy ng vt cng cao mun ti sinh yu cu iu kin nghim khc hn. Bnh hc thy sn 31- Phn ho ca t chc nh hng kh nng ti sinh: T chc phn ho cng cao nng lc ti sinh li cng thp v ngc li nhng khng phi tt c cc t chc ti sinh thp nng lc phn ho u cao. - S pht dc ca c th cng nh hng n ti sinh t bo: T chc c th sinh vt thi k phi thai nng lc ti sinh mnh nht, thi k gi nng lc ti sinh thp. Kh nng ti sinh t b t chc cn quan h n kh nng sinh trng, s kho mnh ca b my tun hon v iu kin dinh dng. - Tnh hnh ca c th nh hng n ti sinh t bo bao gm iu kin sng, trng thi h thng thn kinh, h thng tun hon,... chi phi nng lc ti sinh. Thng c 2 loi ti sinh: - Ti sinh sinh l: L hin tng bnh thng xy ra trong sinh hot, biu hin t bo mi thay th cho t bo gi nh hng cu mi b sung. - Ti sinh bnh l: Di iu kin bnh l t bo mi thay th t bo cht. T chc va ti sinh v kt cu v c nng c th hon ton ging nh t chc c nhng tri li mt s t chc mt i khi thay th t chc mi v kt cu v c nng khc hn ch yu do t chc m ti sinh b sung. 2.2.4.2. Ph v tng sinh ca t bo t chc: Phlchtbotchctnglnvthtch.Tngsinhchtbotchctnglnvs lng. C khi t chc tng ln v th tch cng c khi l kt qu ca c ph v tng sinh. Ph tht l thnh phn thnh t chc c quan to ln hoc t bo chc tng ln, c nng hot ngtngln.ldocnghotngtnghaydotcdngcatuynnititnh ngilaongchntay,vnngvin.Phgilstnglncabphngiancht,b phn t bo chc khng tng ln thm ch cn teo nh, c nng hot ng gim. 2.2.5. U bu: ng vt khng xng sng, c xng sng v thc vt c th pht sinh ra u bu. 2.2.5.1. Khi nim v c tnh ca u bu: U bu l tng s qu ca t bo do cc loi nguyn nhn gy bnh nh vt l, ho hc, sinhvtdnn.Tbotngsinhthnghnhthnhkhiucktcuvcnngkhc thng, kh nng trao i cht v sinh trng rt mnh khng ng nht vi cc t chc c th,phnhocatbokhnghonton,vhnhthignvitbophi,khngcxu hng hnh thnh kt cu t bo t chc bnh thng. Sau khi x l nguyn nhn gy bnh c im trao i cht v sinh trng ca t bo t chc vn tip tc duy tr. Thnh phn ho hc ca t bo t chc u bu so vi t bo t chc bnh thng sai khc v s lng, thnh phn nc nhiu, protein gim, th keo phn tn nn sc trng b mt t bo gim. U bu c 2 loi: U bu hin tnh v u bu c tnh. - U bu hin: tnh sinh trung chm, phn ho ca t bo tng i cao, kt cu v trao i cht gn ging nh t chc bnh thng, lc sinh trung trng to c mng bao bc v vy nn d ct, uy hip tnh mng khng ln. - U bu c tnh: Sinh trng ca t bo nhanh, c th chuyn dch, phn ho khng hon ton, v kt cu trao i cht khng ging t bo bnh thng, sinh trng t v trng to nhng khng hnh thnh mng bao bc nn khng d dng ct i, nguy hi tnh mng sinh vt ln. Hch v nhn tng i ln, nhum mu dch tng v hch t bo bt mu m, trong cng mt t chc t bo to nh khng u, sp xp t bo hn lon khng hnh thnh kt cu ca t chc in hnh. U bu c tnh thng dn n bnh ton thn, lm cho dinh dng khng tt, gy yu, sc khng gim, thiu mu, c th b trng c dn dn hu hoi c th. Bi Quang T322.2.5.2. U bu ca c. C c xng b u bu nhiu hn c xng sn. Qua thng k c hn 60 loi u bu khc nhau, phn b cc c quan khc nhau nn c tn gi khc nhau. -Ubuthngb:lutthngbcctbotchccquan,ddy,rut,tuynsinh dc, tuyn tu, tuyn gip trng, bng quang thn, bong bng, da, mang, mt,rng... -Ubulgiacctchccquankhngtomu:umc,um,uxng,umch mu... - U bu c quan to mu: ch yu u c t chc lm ba. - U t bo sc t: c u bu t bo sc t hn 10 loi nhng u sc t en hay gp hn c. 3. Mi quan h gia cc nhn t gy bnh cho thu sn ng vt thu sn v mi trng sng l mt th thng nht, khi chng mc bnh l kt qu tc ng qua li gia c th v mi trng sng. Khi ng vt thu sn b bnh phi c 3 nhn t. - Mi trng sng. - Tc nhn gy bnh. - Vt ch- ng vt thy sn. 3.1. Mi trng sng- Environment Cc yu t mi trng u l cc mi nguy trong nui trng thy sn, bi v t l sng, sinh sn v sinh trng ca cc loi ng vt thy sn ph thuc vo mi trng thch hp. C nhiu yu t mi trng c kh nng nh hng n nui trng thy sn, nhng ch mt s t c vai tr quyt nh. Nhit v mn l gii hn quan trng ca loi thy sn nui mtaimnhtnh.Muidinhdng,kimtngsvcngtngscngl nhng yu t quan trng iu chnh thc vt pht trin m chng cn nh hng n sinh vtthysinhlthcnchongvtthysn.trongiuchnhnhsngchiuvo nctcngnsquanghpvccchuithcn;trongcngnhhngtrctip n c v ng vt khng xng sng khc. Nhng yu t mi trng khc nh hng cho nuitrngthysnlpH,oxyhatan-DO,carbonic-CO2, ammoniac- NH3, nitrite- NO2 v hydrogen sulfide- H2S. Ngoi ra mt s trng hp gy c do kim loi v thuc tr su cthgynhimtrongnuitrngthysn.Nhngchtgynhimtrongnuitrng thysnthngcnngthphnbtcchtcnoxyratrongphmvihthng nui. 3.1.1. Nhit nc: ngvtthusnlnhmngvtbinnhit,nhitcthcachngchyuph thuc vo nhit nc (mi trng sng), d chng c vn ng thng xuyn, th kt qu vnngsinhranhitkhngngk.Nhitncqucaohocquthpukhng thun li cho i sng ca ng vt thu sn. Nu nhit vt qu gii hn cho php c thdnnngvtthusnchtthmchchthnglotdomimtloingvt thusncngngnhitkhcnhau.Vmangkhinhitncgimxung13-140C, rt ko di c th lm cht tm cng xanh. Nhit di 60C hoc trn 420C lm c r phi cht. Khi nhit nc trong ao l 350C t l sng ca tm s (Penaeus monodon) l 100%, nhng nhit 37,50C tm ch cn sng 60%, nhit 400C t l tm sng 40%. Vi tm lng Penaeus merguiensis 340C t l sng 100%, 360C ch cn 50% tm hot ng bnh thng, 5% tm cht, 380C 50% tm cht, 400C 75% tm cht. Mt s ng vtbst:baba,ra,lngth,chminBcmangchnghontonngnghot ng, khng n v nm tr ng. Bnh hc thy sn 33S thay i t ngt ca nhit (ngay c trong phm vi thch hp) cng c th khin cho ng vt thu sn b sc (stress) m cht. Trong qu trnh vn chuyn, nui dng cn ch s chnh lch nhit v nht l s thay i nhit t ngt. Nu nhit chnh lch 50C c th lm cho ng vt thu sn b sc v cht, tt nht khng nhit chnh lch qu 30C, bin dao ng nhit trong ngy khng qu 50C. Chng ta phi ch khi thi tit thay i nh dng bo, ma ro t ngt, gi mu ng bc trn v lm nhit nc thay i t ngt d gy sc cho ng vt thu sn. unm2002chtnhring3tnhScTrng,BcLiuvCMauxungging 339.000ha,ntrungtunthng3c193.271ha(chim57%)tmbbnhvcht. HintngtmchtmtstnhvenbinNamBunm2002nguynchnhlhin tng El-Nino Nam B nhit khng kh ln 3703 C (theo Phng d bo kh tng, i kh tng thy vn khu vc Nam B- 7/5/2002), thi lng nng ko di trong ngy cao hnmcbnhthng.Trungbnhmtngy,bnhthngthigiannngkodi5-6gi. Nhng hin ti s gi nng trong ngy ko di t 9-10 gi. Do thi tit khc nghit v nng ko di, dn n nhit nc cc m nui tm cng tng cao, chng gy sc lm cho tm nui d b bnh v cht. 3.1.2. trong trong th hin s pht trin ca thc vt ph du trong ao nui. trong c th hn ch rong pht trin y ao. S n hoa ca thc vt ph du tc ng tt vi tm nui v s kch thch ng vt l thc n ca tm pht trin. trong thc vt ph du ci thin tt cho tm, bivchnghnchccchtllng, lm tm nhn ca tm tt hn, gim mi nguy cho tm. trong do nng cc cht mn hu c cao khng gy nguy him trc tip cho tm, nhnggymtcnbngdinhdng,vcthpHgim(axit),dinhdngthp,hnch nh sng chiu qua dn n quang hp km. trong ca thc vt ph du ca ao nui tm tt nht l 30-40cm. 3.1.3. mn mn l tng s cc ion c trong nc, mn n v tnh l phn nghn (). Tng qut ca nc c chia ra 6 loi mn khc nhau: mn mg/lppt () Nc ma30,003 Nc mt300,03 Nc ngm3000,3 Nc ca sng3.0003 Nc bin30.00030 Nc h kn300.000300 Nhngloicbinvcnclcgiihnmnkhcnhau.VdtheoWuvWoo (1983) cho bit c 13 loi c bin trng thnh chu ng c 2 tun mn thp (3, 5 v 10 ), 12 loi sang c mn 10 , 6 loi 5 v 3 loi 3 . Do cho nn mt s loi c bin c kh nng nui c nc l (ca sng). Nhng loi tm bin c cc gii hn mn cc khau, tm lt (Penaeus merguiensis) trong ao nui c mn tt nht l 15, nhng tm s (P. monodon) t l sng v sinh trng tt gii hn mn rng hn l 5-31 v chng c th sinh trng nc ngt mt vi thng(theoBoyd,1987;Chakraborti,1986).Tmchntrng(P.vannamei)nuitrongao gii hn mnt 15-25 v chng c th sinh trng, sng mn thp hn t 0,5-1,0 (theo Boyd, 1989). Bi Quang T34Khi mn ca nc thay i ln ln 10% trong t pht hoc 1 gi lm cho tm mt thng bng. Tm c kh nng thch nghi vi gii hn mn thp hoc cao hn nu thay i t t. Tm postlarvae trong ao nui b sc khi mn thay i t 1-2 trong 1 gi. Khi vn chuyntmpost.t33,nugimmnvitl2,5/githtlsngcapostl 82,2% v gim t l 10/gi th t l sng ca post cn 56,7% (theo Tangko v Wardoyo, 1985). Trong ao nui tm mn bin thin tt nht nh hn t l 5/ngy. 3.1.4. Oxy ho tan: ng vt thu sn sng trong nc nn hm lng oxy ho tan trong nc rt cn thit cho i sng ca ng vt thu sn. Nhu cu oxy ph thuc vo tng loi, tng giai on pht trin, trng thi sinh l, nhit . V d nhit 250C s tiu hao oxy ca c trm c bt l1,53mg/g/h,chng0,51mg/g/h,cging0,4mg/g/h.Khinhittngthlng tiu hao oxy ca c cng tng ln. C nhit i (nc m) yu cu oxy ha tan ln hn 5 mg/l t nht l 16 gi trong mt ngy mvoxyhatannhhn5mg/lkhngqu8gitrongngym,nhngoxyhatan khng thp di 3 mg/l. Duy tr cho mt qun th c ti nht th lng oxy ha tan nh hn 5mg/lkhngqu8gitrongngymvoxyhatankhngthpdi2mg/l(theo McKeevWolf,1963).Doiukinlngoxyhatan3mg/lhocthphnlmi nguy him cho c. th d c vc (chm) nui lng Songkhla- Thi lan cht do mi trng nc b nhim bn trong lng oxy ha tan vo ban m gim xung 1,3 mg/l, khi oxy ha tan 3,10-3,85 mg/l c hin tng c vc cht (theo Tookwinas, 1986). Nhu cu oxy ho tan trong nc ti thiu ca tm l 5 mg/l. Trng hp oxy ho tan thp hn mc gy cht ko di lm cho tm b sc, nh hng xu n t l sng, tng trng v pht dc ca chng. Gii hn gy cht ca oxy ha tan cho tm he Nht Bn (P. japonicus) t 0,7-1,4mg/l (theo Egusa, 1961). Tm s ging (P. monodon) v tm chn trng ging (P. vannamei) gii hn gy cht ca oxy ha tan t 1,17-1,21mg/l (theo Seidman v Lawrence, 1985). Bng 1: S thay i lng tiu hao oxy ca c nhit nc 350C so vi nhit nc 150C (%) Loi cGiai on M trng M hoaTrm c C hng243236220 C gng400342962 Nhu cu oxy ho tan trong nc ti thiu ca c l 3 mg/l, vi tm l 5 mg/l. Trng hp oxyhotanthphnmcgychtkodilmchongvtthusnbsc,nhhng xu n t l sng, tng trng v pht dc ca chng. 3.1.5. Kh Cacbonic - CO2. Kh Cacbonic - CO2 c trong nc l do qu trnh h hp ca ng vt thu sn v s phn hucacchpchthuc.HmlngCO2tdotrongncbnhthng1,5-5,0mg/l. KhiCO2thmlngCO2l25mg/lcthgycchoc.Vdngnggychtc hng m hoa v n ph thuc vo nhit nh sau: Nhit nc 200C ngng gy cht 32,28 mg/l. Nhit nc 250C ngng gy cht 30,18 mg/l. Nhit nc 300C ngng gy cht 28,45 mg/l. Nhit nc 350C ngng gy cht 26,18 mg/l. CO2 trong nuc thng tn ti cc dng: Bnh hc thy sn 35CO2 + H2O H2CO3 MT kim H2CO3HCO3- + H+ MT axit 3.1.5. pH pH ca nc nh hng rt ln n i sng ca ng vt thu sinh. Tuy phm vi thch ng pH ca c tng i rng; c bin pH = 7,5 - 9,0 l ti u, pH thp di 4 hoc cao qu 11 c th lm cho c cht. Thay i pH t ngt cng lm cho c b sc, nu thay i pH qu gii hn thch nghi ca loi th c cht. V d vn chuyn c hi (theo Witschi v Ziebell, 1979) t mi trng nc pH 7,2 n mi trng pH 7,2; 8,5; 9,0; 9,5 v 10. T l sng sau 48 gi nh sau: pH 7,2 t l sng 100%; pH 8,5 - 100%; pH 9,0 - 88%; pH 9,5 68%;pH100%.BinthayipHtheonvthigiannhhngrtlnntl sngca c. Th nghim ca Murray v Ziebell (1984) cho bit t l cht ca c hi 40% khi nui iu kin pH thay i t 8,0-9,7 trong 5 gi. Nhng thigian thay i l 5 ngy tpH8,0ln9,7ttcchikhngcht.Vd:MtskhuvcngbngSngCu Long b x phn ma nc l pH ca nc gim xung di 5 thm ch gim cn pH = 3-4, gy sc cho ng vt thu sn nui nh tm s nm 1994 Minh hi, Tr Vinh. TrongaonuitmpHbinitheotheosquanghpcathcvttrongngy.Nch mkmththngbuisngsmkhimttrichamcpHl6vbuichiul9 hoc cao hn. Do trong ao nui tm thng xuyn gi nc c kim thp cn bng pHtngcaokhiqutrnhquanghpmnh.Cmtstrnghpkimcao,cng thp pH tng ln 10 khi qu trnh quang hp mnh (theo Wu v Boyd, 1990). Bui chiu pH qu cao c th gy cht u trng tm v ng vt ph du. Thi tit kh hn, nc tng mt bc hi c th pH cao (nc kim) v khng ph hp cho nui tm. Trong ao nui tm pH tt nht t 7,5-8,5 v bin thin trong ngy khng qu 0,5 n v. 3.1.6. Kh Chlo: Trongiukintnhin,ncccthuvckhngcClo.Chloxuthindosnhim bn,ngungcchnhlccchtthinhmy,xnghipcngnghip.TrongncClo thng dng: HOCl- hocCl-: Cl2 + H2OHOCl + Cl- + H+ MT kim HOCLH+ + OCl- MT axit OCl- ( O ) + Cl- Oxy nguyn t l cht oxy ho mnh, c th nh hng n mang c ngay c khi hm lng Clo thp. Vi pH = 6: 96% Clo ha tan tn ti di dng HOCl. Vi pH = 9: 97% HOCl b hp th Chlo di dng HOCl c hn OCl-. ccaClophthucvonhitnc,pH,hmlngoxyhotan.Vihm lngClotrongnc0,2-0,3mg/lcbchtrtnhanh.Trongkhongthigiandi30 pht,nngchophpcaClocthl0,05mg/l.Nngchophptrongccaonui tm, c l < 0,003 mg/l. Bi Quang T363.1.7. kim kim trong nc ch yu l cc ion HCO3- (bicarbonate kim), CO32- (carbonate kim), OH- (Hydroxit kim), n v tnh biu th tng ng mg/l CaCO3. Trong nc t nhin kim khong 40mg/l hoc cao hn, nc c kim cao gi l nc cng, nc c kim thp gi l nc mm. Theo Movle nc cng cho nng sut nui tm cao hn nc mm. kim phn nh trong nc c cha ion CO32- nhiu hay t, trong ao nui tm c s bin i ln v kim, thp nht 5mg/l v cao ln hng trm mg/l. kim tc ng n h m cn bng pH: NuthmCO2thnccchabicarbonatehoccarbonate,pHsgim.pHgimdokt qu phn ng ca ion hydrogen (H+) vi CO32- hoc HCO3-. Trong nc t nhin, CO2 l do qu trnh h hp ca sinh vt v khuych tn t khng kh vo, s CO2 khuych tn t khng khvokhngngk.LngCO2tnghocgimlnguynnhnlmchopHthayi. Bicarbonate l h m chng li thay i t ngt ca pH. Nu H+ tng, th H+ phn ng vi HCO3- to thnh CO2 v nc, trong khi hng s K khng i do pH ch thay i nh. TngOH-ktquchlmgimH+bivCO2vH2OphnngmnhhnviH+,do hng s K khng i v ngn cn c s thay i ln pH. H m c biu th bng cng thc sau: [HCO3-] pH = pK1 + log [ CO2] Trong h m CO2 l axit v ion HCO3- l dng mui. Vic tnh ton CO2 v HCO3- l rt kh v lng ca chng rt nh. Tuy nhin nc c kim cao c h m mnh hn nc c kim thp. Thnh phn c bn ca kim gm: CO32-, HCO3-, OH-, SiO4-3, PO43-, NH3 v cc cht hu c khc, tuy nhin hm lng ch yu c trong nc l CO32-, HCO3-, OH-. CO2 trong nc t nhin phn ng vi bicarbonate ca v t, nh hai khong kim l vi (CaCO3) v dolomite [CaMg(CO3)2] CaCO3 + CO2 +H2O Ca2+ + 2HCO3- (1) CaMg(CO3)2+2 CO2+ 2H2OCa2++ Mg2+ +4HCO3- (2) Hai khong cht trn khi s dng u tng kim, nh dolomite (2) cho lng bicarbonate tng gp i vi. Trongaonuitmckimthp, hmyupHsdaonglntrongngy,chonn cn b xung dolomite nng cao kim lm cho h m mnh s iu chnh n nh pH trong ngy. 3.1.8. Kh Ammoniac - NH3. Ammoniac-NH3ctothnhtrongncdoccchtthicanhmyhochtvs phn gii cc cht hu c trong nc: NH3 + H2O NH4OH MT axit NH4OHNH+ + OH- MT kimBnh hc thy sn 37S tn ti NH3 v NH4+ trong nc ph thuc vo nhit , pH v mn ca nc (xem bng 2 v 3), NH3 rt c i vi tm. Nc cng mang tnh axit ( pH thp), NH3 cng chuynsangNH4+tc,mitrngcngkimNH3cngbnvngvgycchotm. Nng NH3 thp 0,09 mg/l gy cho tm cng xanh chm pht trin v nng 0,45 mg/l s lm gim tc sinh trng ca tm he (Penaeus spp) i 50%. Nng NH3 gy cht50%postlarvaetms:LC50-24hl5,71mg/lvLC50-96hl1,26mg/l.Nng NH3 gii hn an ton trong ao nui l 0,13mg/l (theo Chen v Chin, 1988). Bng 2: So snh t l % NH3 khc nhau trong nc ngt v nc l, nhit 240C T l % ca ammonia Nc l c mn ()pHNc ngt 18-2223-2728-31 7,62,051,861,741,70 8,04,994,544,254,16 8,411,6510,7010,09,83 Bng 3: T l % NH3 khc nhau theo pH v nhit ca nc ngt Nhit 0CpH 222426283032 7,00,460,52 0,60 0,70 0,81 0,95 7,20,720,82 0,95 1,10 1,27 1,50 7,41,141,30 1,50 1,73 2,00 2,36 7,61,792,05 2,35 2,72 3,13 3,69 7,82,803,21 3,68 4,24 4,88 5,72 8,04,374,99 5,71 6,55 7,52 8,77 8,26,767,68 8,7510,0011,4113,22 8,410,30 11,6513,2014,9816,9619,46 8,615,4017,2819,4221,8324,4527,68 8,822,3824,8827,6430,6833,9037,76 9,031,3734,4237,7141,2344,8449,02 9,242,0145,4148,9652,6556,3060,38 9,453,4556,8660,3363,7967,1270,72 9,664,5467,6370,6773,6376,3979,29 9,874,2576,8179,2581,5783,6885,85 10,082,0584,0085,8287,5289,0590,58 10,287,8789,2790,5691,7592,8093,84 1.1.9. Nitrite- NO2 Nitritecsinhradoqutrnhchuynhatmammonnhccvikhunnit (Nitrobacter): NH4+ + O2 NO2- + H+ + H2O NO2- + O2 NO3- Nu mi trng thiu oxy th qu trnh chuyn ha m ch n nitrite (NO2) khi ng vt thy sn hp thu phn ng vi Hemoglobin to thnh Methemoglobin: Hb + NO2-=Met-Hb Bi Quang T38Phnngnysttrongnhnhemoglobincamucboxyhathnhst,ktqu methemoglobin mt kh nng vn chuyn oxy. Nitrite gy c mu c v chuyn thnh mu nu.gipxccutohemocyaninlCutrongnhnthayst.Phnngcanitritevi hemocyanin km, nhng nitrite cng c th gy c cho gip xc. Nng gy cht 50% 96 h (LC50- 96h) tm nc ngt t 8,5-15,4 mg/l. Tm cng xanh chm pht trin nng nitrite 1,8-6,2 mg/l (theo Colt, 1981). Nc l do c nng canxi v clo cao nn c t ca nitrite gim, v d postlarvae tm s (P. monodon) c LC50-24h l 204mg/l v LC50-96 l 45mg/l (Chen v Chin, 1988).

1.1.10. Sulfide hydro - H2S. H2Scsinhradophnhuccchthuccchaluhunhdovisinhvt,cbit trongiukinymkh(thiuoxy).KhcH2Snhhngnsckhocatmph thuc v pH ca nc, nu pH thp H2S s rt c (xem bng 4). Nng H2S trong ao nui cho php l 0,02 mg/l. Bng 4: T l % H2S khc nhau theo nhit pH ca nc Nhit 0 CpH 222426283032 5,099,199,199,098,998,998,9 5,597,397,196,996,796,596,3 6,092,091,490,890,389,789,1 6,578,177,075,874,673,472,1 7,053,051,449,748,246,645,0 7,526,325,023,822,721,620,6 8,010,19,69,08,58,07,6 8,53,43,23,02,92,72,5 9,01,11,01,00,90,90,8 V d tm he (Penaeus japonicus) mt thng bng khi H2S l 0,1-0,2 mg/l v cht khi H2S l 0,4 mg/l. Cc khu vc nui thm canh c nhiu ao nui nn y khng ty dn sch hm lng H2S trong nc ao nui c bit l y ao c mi thi ca H2S, y l mt trong nng nguyn nhn gy cho ng vt thy sn b sc v lm chng c th cht. Qua kho st khi hm lng H2S trong nc l 0,037-0,093 mg/l th trong lp bn su 2 cm, hm lng H2S l 10 mg/l. 3.1.11. Cc kim loi nng: Mt s kim loi nng: Fe, Cu, Zn, Hg, Pb, Al.....lng ho tan trong nc v y ao vi s lng t. Cc kim loi thng dng mui ho tan trong nc cng, hoc cc ion kim loi kttadidngCacbannat.Cclpbnyaohpthphnlnccionkimloilm gim ng k nng ion kim loi trong nc. Tnh c ca chng trong nc thng thp, ng vt thu sn ch b nh hng do cc ngun nc thi cng nghip a vo thu vc khng c x l (bng 5). Bng 5: c tnh ca kim loi nng vi ng vt thy sn (theo Boyd, 1987) Kim loi LC50 96 h (g/l)Gii hn an ton (g/l) Cadnium- Cd80-42010 Chromium- Cr2.000-20.000100 ng- Cu300-1.00025 Ch- Pb 1.000-40.000100 Thy ngn- Hg10-400,10 Thic- Zn1.000-10.000100 Bnh hc thy sn 391.1.12. Thuc tr su Mt s thuc tr su dng cho nng nghip v chng vo cc dng sng. Lng gy c tnh ca nhiu loi thuc tr su thng t 5-100m/l (Cope, 1964) v c mt s loi c tnh nng thp hn. Mi trng nhim thuc tr su c th khng dit hng loi tm trng thnh, nhng l mi nguy cho qun th tm, sinh vt thy sinh km pht trin v suytn.ThuctrsunhmChlorinatehydrocarbonnguyhimnhtchotmc,clc ca nhm ny gy hi cho c ng vt thy sinh nc ngt v nc mn (xem bng 6). Thucditcdngtrongnngnghipcthnhimtrongccaonuitrngthysn. Chngkhnggycchongvtthysnnhngchngcthgycphytoplankton (thcvtphdu).Vd:Tucker(1987)chobitrngthucditcPropanil[N-(3,4-dichlorophenyl)propanamide],thngdngphunvorungladitcdi,thchng lm gim kh nng sn xut oxy ca nhm thc vt ph du, vi nng ca Propanil mc 20-50g/l lm gim 25% qu trnh sn sinh oxy. Bng 6: c tnh ca mt s thuc tr su vi ng vt thy sn (theo Boyd, 1987) Thuc tr su LC50 96 h (g/l)Gii hn an ton (g/l) Aldrin/Dieldrin0,20-16,00,003 BHC0,17-2404,00 Chlordane5-3.0000,01 DDT0,24-2,00,01 Endrin0,13-120,004 Heptachlor0,10-2300,001 Toxaphene1-160,005 3.2. Tc nhn gy bnh (Mm bnh)- Pathogen Tc nhn gy bnh l cc yu t hu sinh lm cho ng vt thu sn mc bnh gi chung l tc nhn gy bnh. Nhng tc nhn gy bnh ny do s cm nhim ca ng vt thu sn l vtchhocsxmnhpcuchngvovtch.Cctcnhngybnhcchiara3 nhm: -Tc nhn gy bnh truyn nhim: Virus, Ricketsia, vi khun, nm,. -Tc nhn gy bnh k sinh: Nguyn sinh ng vt (ng vt n bo), giun sn, a,, gip xc...(ng vt a bo). -Mt s sinh vt trc tip n ng vt thu sinh hay uy hip ng vt thu sinh: Cn trng nc, rong to c, sa, c d, ch, rn, ba ba, chim , ri c...v c gi l nhm ch hi ca ng vt thu sinh. 3.3. Vt ch (ng vt thy sn)- Host Cc nhn t ngoi cnh (yu t v sinh v hu sinh) tc ng th ng vt thu sn khng th mc bnh c m n ph thuc vo sc khng ca c th vi tng bnh ca vt ch: Vt ch thng biu hin bng nhng phn ng vi mi trng thay i. Nhng phn ng ca c th c th ko di 2-3 ngy hoc 2-3 tun tu theo mc ca bnh. 3.4. Mi quan h gia cc nhn t gy bnh cho thu sn. ng vt thu sn sng trong nc hay ni mt cch khc nc l mi trng sng ca ngvtthusn.ngvtthusnsngcphicmitrngsngtt,ngthi chng cng phi c kh nng thch ng vi mi trng. Nu mi trng sng ca ng vt Bi Quang T40thu sn xy ra nhng thay i khng c li cho chng, nhng con no thch ng s duy tr c cuc sng, nhng con no khng thch ng th s mc bnh hoc cht. ng vt thu sn mc bnh l kt qu tc dng ln nhau gia c th v mi trng sng. V vy, nhng nguyn nhan gy bnh cho ng vt thu sn gm 3 nhn t sau: - Mi trng sng (1): To, pH, O2, CO2, NH3, NO2, kim loi nng,..., nhng yu t ny thay ibtlichongvtthusnvtoiukinthunlichotcnhngybnh(mm bnh) dn n ng vt thu sn d mc bnh. - Tc nhn gy bnh (mm bnh - 2): Vurus, Vi khun, Nm, K sinh trng v nhng sinh vt hi khc. - Vt ch (3) c sc khng hoc mn cm vi cc tc nhn gy bnh l cho ng vt thu sn chng c bnh hoc d mc bnh. Mi quan h ca cc nhn tgy bnh khi ba nhn t 1,2,3 th ng vt thy sn mi c th mc bnh (hnh 1): nu thiu 1 trong 3 nhn t th ng vt thu sn khng b mc bnh (hnh 2-4). Gi mi trng nui tt s tng sc khng vi mm bnh cho ng vt thu sn, tuy ng vt thu sn c mang mm bnh th bnh khng th pht sinh c (hnh v 2). ngn cn nhng nhn t trn khng thay i xu cho ng vt thu sn th con ngi, k thut nui phi tc ng vo 3 yu t nh: ci to ao tt, ty trng ao h dit mm bnh, th ging tt, cung cp thc n y v cht v lng th bnh rt kh xut hin. Khinmc3nhnttrncmiquanhmtthit,doxemxtnguynnhngy bnh cho ng vt thu sn khng nn kim tra mt yu t n c no m phi xt c 3 yu t: mi trng, mm bnh, vt ch. ng thi khi a ra bin php phng v tr bnh cng phi quan tm n 3 nhn t trn, nhn t no d lm chng ta x l trc. V d thay i mi trng tt cho ng vt thu sn l mt bin php phng bnh (hnh 2). Tiu dit mmbnhbnghocht,thucsngnchncbnhkhngphttrinnng(hnh3). Cui cng chn nhng ging ng vt thu sn c sc khng vi nhng bnh thng gp gy nguy him cho ng vt thu sn (hnh4). Hnh 1:Mi quan h gia cc nhn t gy bnh: Vng xut hin bnh (mu ) c ba yu t gy bnh 1+2+3; Vng 1+2 bnh khng xy ra; Vng 2+3 bnh khng xy ra; Vng 1+3 Bnh1+2+3Vt ch 3 1+32+31+2Mi trng 1 Mm bnh 2Bnh hc thy sn 41 Hnh 2: Khng xut hin bnh do mi trng tt, khng ba nhn t gy bnh Hnh 3: Khng xut hin bnh do khng c mm bnh, khng ba nhn t gy bnh. Hnh4:Khngxuthinbnhdovtchcsckhngcao,khngbanhntgy bnh Vt ch 3 2+3Mi trng 1Mm bnh 2Vt ch 31+3Mi trng 1Mm bnh 2 Vt ch 31+2Mi trng 1 Mm bnh 2 Bi Quang T42Ngi ta c th biu din mui quan h gia nguyn nhn v iu kin gy bnh ng vt thy sn bng cng thc ton hc: D = P + H + E2

D- Disease (bnh);P- Pathogen (tc nhn gy bnh);H- Host (vt ch);E- Environment (mi trng) Cngthctrnkhngnhvaitrquytnhnguynnhngybnh(P)vvaitrquan trngcaccnhntiukin(HvE),nhngnhnmnhtmquantrngcaiu kin mi trng (E2) trong qu trnh pht sinh bnh. 4. Phng php chn on bnh phng tr c bnh tt, trc tin phi chn on c bnh mi c th ra cc bin php phng tr bnh c hu hiu. Cc bc tin hnh chn on bnh nh sau: 4.1. iu tra hin trng: ng vt thu sn mc bnh khng nhng biu hin cc du hiu bnh l trn c th,m cnthhincchintngtrongao.Khichintngngvtthusnchttrongao, ngoi ci cht do ng vt thu sn mc bnh m c th do mi trng nc b nhim bn, nhim c t nh cc cht thi ca nh my cng nghip thi ra, do nc sinh hot ca th trn, th x , thnh ph thi ra, do phun thuc tr su ca nng nghip...cng s lm cho c tm cht. Do cn phi kim tra hin trng bao gm cc ni dung sau. 4.1.1. Tm hiu cc hin tng ng vt thu sn b bnh th hin trong ao: Nh ta bit qu trnh pht sinh bnh c 2 loi: loi cp tnh v loi mn tnh: - ng vt thu sn b bnh cp tnh thng c mu sc v th trng khng khc vi c th bnh thng, ch nhng ni b bnh mi thay i. C th b bnh cht ngay v t l cht tng ln rt nhanh, trong thi gian ngn t n nh cao nht (2-3 ngy). -ngvtthusnbbnhmntnhthngmusccthhiti(enxm),thtrng gyyu,tchnbiltrnmtnchocquanhbao,tlchttnglnttm trong thi gian di mi t nh cao (2-3 tun). - Nu mi trng nc nhim c th t nhin ng vt thu sn cht hng lot. Do cn tm hiu k cc hin tng bnh ca ng vt thu sn chn on bnh mt cch chnh xc. o cc ch tiu mi trng nc, so snh vi cc gii hn cho php nui ng vt thu sn. 4.1.2. iu tra tnh hnh qun l chm sc. ng vt thu sn mc bnh c lin quan n vn chm sc v qun l ao: Bn phn qu nhiu,chtlngthcnkmphmcht,chonqunhiu...ddnnchtlngnc thay i: Oxy ho tan gim, nh hng n sc kho ca ng vt thu sn. Ngc li bn phn t, thc n khng , mi trng nc ngho, ng vt thu sn gy yu d b bnh tn cng. 4.1.3. iu tra tnh hnh bin i thi tit kh hu thu ho v sinh vt gy hi . Trongmavnuingvtthusnkhngthchhp:Nngqu,rtqu,magitht thng, thu triu kit...u l nhng yu t ngoi cnh nh hng n sc kho ca ng vt thu sn. Do chng ta cn phi iu tra thi gian trc t 5-7 ngy v cc ch thuhocaaonui trng thu sn; t0, pH, trong, oxy ho tan, NH3, H2S, NO2... phn tch cho ng vt thu sn nui. Mt s sinh vt gy hi cho VTS: to c, sa, c d, lng th, b st, chim v ng vt c v Bnh hc thy sn 434.2. Kim tra c th ng vt thu sn. 4.2.1. Kim tra bng mt thng: Kim tra bng mt thng l mt phng php ch yu kim tra bnh l tm cc tc nhn gy bnh ch b bnh hoc cc hin tng phn ng ca c th i vi tc nhn gy bnh. i vi k sinh trng ln nh: Gip xc, nm thu my...c th nhn thy bng mt thng c. Nhng mt s tc nhn gy bnh nh: Vi khun, k sinh n bo.. mt thng khng thnhnthyc,nhngchngtacthdavoccduhiubnhl:Bnhkhun thng biu hin xut huyt vim, thi ra, hoi t, dng vy, n mn v...Cc bnh k sinh trng thng th hin tit nhiu cht nhn, chy mu hoc c cc bo nang thnh chm nh. Do cn phi xem xt t m cc du hiu chn on bnh trn cc b phn nh sau: - Kim tra trn da, v: i vi c c th dt c trn khay men theo th t quan st t u n ming, mt, np mang, vy, vy, tia vy c cc tc nhn gy bnh; Nm thu my, rn c, trng m neo, a, giun, bo nang ca k sinh n bo (Myxobolus). i vi tm: Cc sinhvtbmtrnv,trnccphnph:Ru,chn,ui,snmn,enrucavv phn ph. -Kimtramang:ivickimtracctmangvnpmangcngmlibnh thng, trn t mang c nhiu nht hay khng, dnh bn v k sinh trng, gip xc, sn n ch k sinh. i vi tm c Isopod k sinh trong mang. - Kim tra ni tng: Kim tra ton b h tiu ho ca c, d dy, rut c thc n khng, c hi khng, trn thnh c xut huyt khng, giun sn k sinh trong d dy rut. Kim tra c quan khc; gan, thn, l lch, bng hi c cc bo nang ca giun sn, im xut huyt ca bnh vi khun. Tm kim ta gan, tu, mu sc... 4.2.2. Kim tra bng knh hin vi: Kimtraccchbbnhmmtthngkhngquanstc:Soiknhkimtraksinh trng n bo, giun sn nh. i vi tm nhum ti gan tu bng xanh malachite kim tra th n bnh MBV (Monodon baculovirus)... Kim tra tm Qu trnh pht sinh bnh c 2 loi: bnh cp tnh v bnh mn tnh: Bnh cp tnh: tm c mu sc v th trng khng khc vi bnh thng