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Aquaculture, 35 (1983) 57-71 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
57
THE PRODUCTION OF THE FRESHWATER PRAWN MACROBRACHIUM ROSENBERGII IN ISRAEL. III. DENSITY EFFECT OF ALL-MALE TILAPIA HYBRIDS ON PRAWN YIELD CHARACTERS IN POLYCULTURE
DAN COHEN and ZIVA RA’ANAN*
Department of Environmental Biology, Life Sciences Institute, The Hebrew University of Jerusalem (Israel)
*Present address: Aquaculture Production Technology (Israel) Ltd., P.O. BOX 4330, Jerusalem 91042 (Israel)
(Accepted 3 November 1982)
ABSTRACT
Cohen, D. and Ra’anan, Z., 1983. The production of the freshwater prawn Macro- brachium rosenbergii in Israel. III. Density effect of all-male Tilapia hybrids on prawn yield characters in polyculture. Aquaculture, 35: 57-71.
The effect of two densities of all male Tilapia hybrids and two procedures for feeding and manuring on Macrobrachium rosenbergii yields and population structure were ex- amined in 22 ponds of 400 m* each. Prawns stocked at 5,000, 10,000 and 15,000 per hectare demonstrated a biomass increase of 586, 1,033 and 1,430 kg ha-’ respectively, during a growout period of 89 days. The average weight was inversely related to prawn stocking density and reached 35.0, 31.0 and 26.1 g respectively. Both the total prawn yields and the average weights were independent of Tilapia stocking rates and of the feeding-manuring strategy. Prawn yields and average weights were affected by the den- sity of the prawn population alone. Survival rates in all cases were above 85% and did not correlate with either prawn or Tilapia stocking rates, nor with feeding strategy.
M. rosen bergii population analysis was performed with respect to size distribution and morphotypic variation and characterization. These parameters were found to be affected solely by prawn density and were independent of the number of Tilapia stocked and the feeding strategies tested.
Contrary to prawn performance, the growth of Tilapia was strongly affected by its stocking density and by the feeding-manuring strategy. The combined yields of Tilapia and common carp varied between 8,400 and 12,000 kg ha-’ year-‘, for the different prawn densities.
INTRODUCTION
The development of growout production procedures for prawns in general and M. rosenbergii in particular relies almost entirely on the monoculture strategy (Shang, 1981). Due to the benthic nature of this organism, only the pond bottom is utilized, thus limiting the prawn yield potential of the whole
0044-8486/83/$03.00 0 1983 Elsevier Science Publishers B.V.
58
pond. Moreover, in the absence of fish, there is no biological control over the development of zooplankton, phytoplankton and filamentous algae, thus re- sulting in ecological instability of the water column (Baissac, 1976; Barnes, 1980). The positive effect of fish on the overall ecological state of the pond has been shown (Malecha et al., 1981; Cohen et al., 1983).
We have demonstrated (Cohen et al., 1983) that the addition of common carp, grass carp and silver carp at low densities improved the ecological main- tenance of the pond without affecting prawn production. We have further demonstrated that juvenile prawns introduced into large fish ponds (668 ha), with a multitude of fish types stocked at amounts above those which are needed for sanitary purposes, resulted in a commercial crop of both fish and prawns.
Bearing in mind that each of the fish species stocked occupies a specific trophic niche (Tang, 1970), and that the commercial yield of prawns in poly- culture is determined by the availability of natural food and by the complex social structure of M. rosenbergii populations (Brody et al., 1980), it was of interest to examine the effect of feeding and manuring procedures and of Tilapia stocking rates on prawn yields and yield characters. The first factor was selected for examination because in a polyculture system the prawns are at a disadvantage if they attempt to reach the supplemental feed due to com- petition with fish. The second factor was selected because of the predomi- nant economic significance of Tilapia in such systems.
In this study, we report on prawn yields and changes in prawn population structure at three different densities of prawns, two densities of Tilapia and employing two different feeding and manuring procedures.
MATERIALS AND METHODS
Pond management procedures
Twenty-one earthen ponds of 400 mZ each, located at ‘Do? Experimental Station, were used in this study. The prevailing water temperature during the growth period was 24-28°C. Water exchange was minimal, in amounts needed to compensate for water seepage and evaporation. Pond management procedures for feeding, manuring and fertilization were similar to those de- scribed previously (Moav et al., 1977).
Feed was administered using a demand feeder located at one edge of the pond. Two management modifications were practised: (a) Common carp pellets, 25% protein, in normal amounts and manuring
once per week (St. C. & W.M.). (b) Sorghum-based pellets administered at one third of the normal amount
with daily manuring (S.P. & D.M.).
59
Stocking of fish
The types of fish stocked in this experiment were: (a) Common carp (Cyprinus carpio L.) which were stocked at an average
weight of 24 g and a density of 3000 ha-‘. (b) Tilapiu male hybrids, which were stocked at an average weight of 25-28
g and a density of 3000 ha-l in one treatment and 7500 ha-l in the second treatment.
(c) Grass carp (Ctenopharyngodon idella) were stocked at an average weight of 375 g and a density of 180 ha-‘.
(d) Silver carp (HypophthaZmichthys molitrix) were stocked at an average weight of 275 g and a density of 400 ha-l.
In all cases the fish were stocked several days prior to the prawns.
Stocking of prawns
Juvenile prawns, nursed in tanks at a density of 4 1-l to an average weight of 1.0 g were transferred in well-aerated tanks from a closed-system nursery, located in the Hebrew University of Jerusalem and operated by Aquaculture Production Technology, Israel (Ltd.), to the experimental ponds at the research station in Dor. They were stocked at three different densities: 15,000, 10,000 and 5,000 ha-‘. In all cases, prawns were counted individual- ly during stocking which was performed late in the afternoon, when fish are less active, in order to allow the prawns time to readjust to the new environment. The prawns were not fed intentionally but derived their diet solely from the natural productivity of the pond, and from the residual supplemented feed supplied to the fish.
Experimental groups
The experiment was designed to have the following treatment groups:
Group No. Feeding strategy
A-I S.P. & D.M. A-II S.P. & D.M. A-III S.P. & D.M. B-I St.C. & W.M. B-II St.C. & W.M. B-III St.C. & W.M.
Tilapia density (No. ha-‘)
7,500 7,500 7,500 3,000 3,000 3,000
Prawn density (No. ha-‘)
15,000 10,000
5,000 15,000 10,000
5,000
Measurements
Ninety days after stocking the prawns, the ponds were harvested. Fish were sorted out according to types, counted and weighed. Prawns from each
TA
BL
E
I
Pra
wn
an
d fi
sh y
ield
s af
ter
a go
-day
gr
owou
t pe
riod
Sto
ckin
g P
ond
den
sity
* n
o.
(no.
h
a-‘)
Av.
wei
ght
at s
tock
ing
Av.
w
eigh
t at
har
vest
F
inal
yi
elds
(a
dded
S
urv
ival
(%
)
(9)
(g)
biom
ass
kg h
a-’
year
-‘)
Pra
wn
s T
ilap
ia
Car
p P
raw
ns
Til
apia
C
arp
Pra
wn
s T
ilap
ia
Car
p P
raw
ns
Til
apia
C
arp
A-I
: P
. 15
,000
13
T
. 7,
500
14
25
17
18
Ave
rage
A-I
I:
P.
10,0
00
16
T.
7,50
0 19
20
23
24
28
Ave
rage
A-I
II:
P.
5,00
0 15
T
. 7,
500
21
22
27
Ave
rage
B-I
: P
. 15
,000
29
T
. 7,
500
B-I
I:
P.
10,0
00
31
T.
3,00
0 32
Ave
rage
B-I
II:
P.
5,00
0 33
T
. 3,
000
34
Ave
rage
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
18.0
22
.4
27.0
25
.1
25.2
25
.7
27.1
24
.5
22.3
32
.8
23.6
28
.8
20.5
24
.0
26.7
24.7
23
.9
26.1
29.7
24
.7
27.9
23
.4
24.6
29
.9
35.1
23
.8
32.4
38
.0
23.5
29
.4
19.3
22
.6
33.1
21
.7
24.5
36
.1
27.9
23
.9
31.5
19.7
24
.6
31.5
17
.6
23.6
35
.7
24.5
24
.1
39.9
17
.1
23.5
33
.0
19.7
23
.9
35.0
25.1
21
.5
28.4
22.0
23
.8
34.2
28
.9
23.7
34
.8
25.4
23
.7
34.5
27.9
23
.0
36.6
22
.0
26.0
30
.3
24.9
24
.5
33.4
175.
4 38
0.2
1332
22
2.0
405.
4 12
51
233.
5 41
1.6
1355
16
6.4
428.
7 17
35
184.
6 31
5.1
1478
196.
4 38
8.2
1430
133.
9 45
9.3
752
231.
1 54
7.3
929
181.
7 45
8.7
1270
13
3.3
515.
6 83
1 16
6.5
307.
1 10
58
224.
0 43
0.0
1361
178.
4 45
3.0
1033
211.
9 43
4.0
484
173.
1 36
5.9
536
224.
2 37
3.8
706
154.
2 33
3.8
619
190.
8 37
6.9
586
280.
3 68
1.1
1133
244.
0 87
9.5
1109
29
3.2
637.
3 13
09
269.
6 75
8.4
1209
260.
3 68
1.8
682
268.
0 78
3.0
647
264.
1 73
2.4
664
4580
41
40
86
97.3
96
.7
5840
42
80
85
99.0
94
.2
5680
46
40
3 06
92
.7
100.
0 37
10
4300
10
4 94
.0
89.2
38
00
3400
96
79
.7
97.5
4722
41
52
95.4
92
.5
95.5
1730
47
10
71
65.3
90
.8
5770
46
10
81
93.3
90
.0
3510
48
10
101
83.7
92
.5
2340
53
40
74
86.7
90
.8
4100
30
40
83
93.7
90
.0
6000
45
60
97
99.0
94
.2
3908
45
12
84.5
86
.91
91.4
5550
43
00
80
96.7
88
.3
4540
38
50
78
97.7
94
.2
5770
37
80
91
96.7
90
.8
3990
35
60
97
99.3
95
.8
4962
38
72
86.5
97
.6
92.3
2750
79
10
70
90.8
99
.2
2700
10
350
84
100.
0 10
0.0
3110
69
80
97
98.3
94
.2
2905
86
65
90.5
99
.1
97.1
2450
76
30
96
89.2
95
.9
2680
75
10
110
91.7
82
.6
2560
75
70
103
90.4
89
.2
*P.
= p
raw
ns;
T
. =
Tila
pia;
in a
ddit
ion
, ea
ch
pon
d w
as s
tock
ed
wit
h
3,00
0 co
mm
on
carp
h
a- ‘,
18
0 gr
ass
carp
ha-
’ an
d 40
0 si
lver
car
p h
a-‘.
61
pond were individually measured for: body weight, body length, claw length, claw color, sex and the presence of eggs. Body length was measured from eye orbit to the tip of the telson.
All data collected were analyzed by computer using SPSS, Frequencies routine. Differences in the proportions of males and females were tested by a chi-square contingency table, and statistical significance of differences be- tween the other parameters measured was determined according to NOVA, ONEWAY-RANGES, LSD-test (Nie et al., 1971).
Results for the performance of the various fish in the experimental system and a detailed explanation for the choice of treatments will be described in a separate publication (Wohlfarth and Hulata, in preparation).
RESULTS AND DISCUSSION
Fish and prawn production in a polyculture system
Table I shows yields obtained for the three main commercial crops in this system, namely prawns, Tilapia and common carp. Unfortunately, two ponds went through an ecological collapse which resulted in a total mortal- ity. These ponds were, therefore, excluded from the data analysis.
In all cases, fish production was not affected by the increase in prawn stocking density. The Tilapia stocking density of 7,500 ha-l yielded an added biomass of 4,722,3,902 and 4,962 kg ha-’ year-’ with prawns stocked at 15,000 (group A-I), 10,000 (group A-II) and 5,000 ha-l (group A-III) res- pectively, demonstrating no correlation between prawn stocking density and Tilupia yields. A similar result was found for the Tilapia stocking density of 3,000 ha-’ (groups B-I, B-II and B-III). Common carp stocked at a density of 3,000 ha-l demonstrated an increase in biomass of 4,152, 4,512 and 3,872 kg ha? year-’ for the three prawn stocking densities, demonstrating no correlation between carp yields and prawn stocking density. Growth of both carp and Tilapiu was strongly affected by the change in the number of Tikzpia stocked combined with the change in feeding strategy as can be seen by a comparison between the A and B groups,
Prawn production was not affected by the change in feeding procedures nor by the increase in Tilupiu stocking density, as is shown by a comparison between the yields obtained within the same prawn stocking density in the A groups vs. the B groups. The amount of added biomass correlated directly with the increase of 1,430, 1,033 and 586 kg ha-’ year-l when stocked at a density of 15,000, 10,000 and 5,000 ha-’ respectively (the A groups). The average growth of prawns was inversely related to their own stocking density reaching, within a 9Oday growout period, an average weight of 26.1, 31.5 and 35.0 g for the above three densities respectively. Prawns survival rates were high, above 85% in most cases, in spite of the total number of fish stocked: 11,080 and 6,580 ha-’ in the A and B groups respectively.
This finding illuminates certain aspects of prawn-fish interaction. Firstly,
62
increased Tilupia density does not seem to increase the physical disturbance of, nor the competition for food with, the prawns. Being significantly less mobile than fish and unable to operate the demand feeders, the prawns de- rived their diet from the natural productivity of the pond and from the resid- ual leftovers from feed pellets, supplied via a demand feeder, which were not consumed by the fish (Frankenberg and Smith, 1967). The fact that the vari- ation in prawn yields was affected only by prawn density indicates that prawn nutrition is not a limiting factor under these conditions.
The size distribution of prawns reared under three densities in a polyculture system
Fig. 1 shows the size distribution curves of male and female prawns reared under three stocking densities in a fish-prawn polyculture system. Similar curves were obtained for prawn populations reared under high densities in monoculture (Cohen et al., 1983 in press). The shape of the size distribution
15,000 prawns /ha
G=Z4.09g
tfGZwz63.04
I
10,000 prawns 1 ha
5,000 prawns/ha
,. -, I wz32.79 g
=Gzw = 98.60
Body Weight (g)
Fig. 1. Frequency histograms of body weights of prawns stocked at various densities, after a go-day growout period.
63
curve is strongly related to the complex social structure of this organism (Ra’anan and Cohen, in preparation). The fact that similar curves are ob- tained when prawns are stocked at low densities in a fish-prawn polyculture system indicates that the presence of fish does not interfere with the prawn’s social structure.
We have shown elsewhere (Cohen et al., 1983) that in large commercial ponds, varying from 4-8 ha, where prawns were stocked at an extremely low density of 2,000 ha-’ in polyculture systems, the size distribution of prawns was narrow, with about 90% of the prawns weighing about 45 g. In that study, since survival rates varied from 44-75%, it is highly possible that, due to practical difficulties during harvest, some prawns were left in the pond, probably the smaller individuals, thus leading to a relatively uniform size distribution. In the present study, average growth and size variation were inversely related to density, while the typical shape of the bimodal weight distribution curve was not affected by density.
Table II presents a statistical analysis of the weight distribution of males and females, 90 days after stocking in growout ponds. The average weight of both males and females is inversely related to prawn stocking density within the examined range of 5,000-15,000 prawns ha-‘. Under all stocking densities, the average weight (W), the standard deviation (SD.) and the co- efficient of variation (P.C.V. = 100 S.D./w) of males are higher than those of females.
When the sex ratio is examined, it is found that while under the lowest stocking density (5,000 ha-l), females constituted a higher percentage than males within the total population (55% females vs. 45% males), under the highest stocking density (15,000 ha-‘), males demonstrated a slightly higher frequency than females (51% males vs. 49% females), The differences in the relative frequencies of males and females are not correlated with the overall survival rates, not with Tilupia stocking densities as is demonstrated in Table III.
Smith et al. (1978) report that sex ratios obtained in prawn monoculture systems were generally biased toward females. In 9 out of 13 cases exam- ined, females comprised a significantly larger proportion (55-64%) of the harvested prawns than did males. They found no relationship between sex ratio and stocking density. In the present study, the correlated between sex ratio and stocking density is apparent. Since in this case all juveniles were ob- tained from the same source and were of the same age and average size at stocking, the possibility that the differences in sex ratios were determined before the prawns were stocked in the ponds is ruled out. Since there was no correlation between survival rate and sex ratio, a selective mortality of one of the sexes under the various stocking densities can not account for the cor- relation found between sex ratio and stocking density. Wang et al. (1975) found that, in Hawaiian ponds stocked at relatively high densities, the pro- portion of males exceeded that of females in the harvested populations. This report is in accordance with our findings. It might be possible that certain
TA
BL
E
II
Sta
tist
ical
an
alys
is*
of t
he
wei
ght
dist
ribu
tion
of
m
ales
an
d fe
mal
es,
90
days
af
ter
stoc
kin
g
Pra
wn
st
ock
ing
den
sity
(n
o.
ha-
l)
15,0
00
Gro
up*
A
A
A
A
A
B
Pon
d n
o.
Fem
ales
M
ales
;“g)
S.D
. P
.C.V
. F
requ
ency
ii
, S
D.
P.C
.V.
Fre
quen
cy
W)
(g)
(%)
13
23.6
0 7.
98
33.8
1 49
.0
30.2
4 18
.31
60.5
5 51
.0
14
23.7
4 7.
60
32.0
1 48
.8
27.5
0 17
.11
62.2
2 51
.2
25
21.8
0 6.
51
29.8
6 49
.7
22.7
3 15
.30
67.3
1 50
.3
17
26.8
7 9.
86
36.6
9 49
.0
30.7
0 19
.40
63.1
9 51
.0
18
24.4
3 7.
76
31.7
6 46
.2
28.6
5 17
.71
61.8
1 53
.8
29
23.9
2 6.
50
27.1
7 49
.5
32.7
9 17
.21
52.4
8 50
.5
Ave
rage
24
.06
7.70
31
.88
48.7
28
.77
17.5
1 61
.26
51.3
10,0
00
A
A
A
A
A
A
B
B
16
26.2
3 7.
59
28.9
4 52
.6
29.6
7 16
.93
57.0
6 19
29
.09
10.0
9 34
.68
42.8
30
.52
19.8
1 64
.91
20
29.4
0 9.
44
32.1
1 47
.7
35.1
9 18
.71
53.1
7 23
26
.57
8.04
30
.26
46.6
31
.91
18.4
3 57
.76
24
29.3
2 9.
41
32.0
9 47
.3
36.4
3 21
.43
58.8
2 28
32
.10
8.90
27
.72
50.6
40
.21
21.4
9 53
.44
31
27.3
9 8.
25
30.1
2 37
.7
37.7
6 18
.85
49.9
2 32
31
.28
9.07
29
.00
51.7
38
.50
19.7
1 51
.19
Ave
rage
28
.92
8.85
30
.61
47.1
35
.02
19.4
2 55
.78
47.4
57
.2
52.3
53
.4
52.7
49
.4
63.2
48
.3
52.9
5,00
0 A
15
31
.79
11.0
34
.60
52.2
31
.14
19.9
7 64
.13
47.8
A
21
34
.15
9.18
26
.88
63.0
38
.24
17.6
5 46
.15
37.0
A
22
34
.52
10.4
1 30
.16
56.9
47
.16
18.5
3 39
.29
43.1
A
27
30
.69
9.12
29
.72
52.1
35
.44
24.3
6 68
.73
47.9
B
33
33
.19
9.42
28
.38
51.3
40
.15
18.2
9 45
.55
48.7
B
34
28
.70
9.36
32
.61
56.6
32
.39
18.9
4 58
.47
43.4
Ave
rage
32
.17
9.75
30
.39
55.3
37
.42
19.6
2 53
.72
44.7
*ii,
= A
vera
ge
wei
ght;
S
D.
= s
tan
dard
de
viat
ion
; P
.C.V
. =
per
cen
t co
effi
cien
t of
va
riat
ion
(1
00
X
(S.D
./%))
. **
Gro
up
A =
Til
upi
a:
7,50
0 h
a-‘,
feed
: so
rgh
um
pe
llet
s;
Gro
up
B =
Til
upi
a:
3,00
0 h
a-‘,
feed
: st
anda
rd
carp
pe
llet
s.
65
TABLE III
The relationship between final survival rate and male-female frequencies
Pond no.* Tilapia stocking Prawn density (ha-’ ) survival (%)
Frequency (%) **
Females Males
29 3,000 70 49.5 50.5 16 7,500 71 52.6 47.4 23 7,500 74 46.6 53.4 21 7,500 78 63.0 37.0 15 7,500 80 52.2 47.8 19 7,500 81 42.8 57.2 24 7,500 83 47.3 52.7 31 3,000 84 37.7 63.2 14 7,500 85 48.8 51.2 13 7,500 86 49.0 51.0 22 7,500 91 56.9 43.1 18 7,500 96 46.2 53.8 33 3,000 96 51.3 48.7 28 7,500 97 50.6 49.4 27 7,500 97 52.1 47.9 32 3,000 97 51.7 48.3 20 7,500 101 47.7 52.3 17 7,500 104 49.0 51.0 25 7,500 106 49.7 50.3 34 3,000 110 56.6 43.4
*Ponds listed in order of increasing survival rates. **Higher frequency of males or females in each pond is underlined.
environmental conditions within the pond, including stocking density, would favor the development of one sex over the other. Presently, we have no ex- planation for either the mechanism behind this phenomenon or its rationale.
Population analysis of prawns
We have previously demonstrated (Brody et al., 1980) that the economic yield characters of M. rosenbergii are determined by the morphotypic varia- tion and the population structure. It was of interest, therefore, to examine the effect of increased Tilapia stocking and feeding strategy on the prawn’s yield characters. We examined the effect of prawn stocking density on mor- phological characteristics of prawn subpopulations classified according to morphotypes. These morphotypes were: a. blue claw (BC) males; b. orange claw (OC) males; c. small males (SM); d. females (F); e. females with eggs (FE).
Table IV presents the relative frequency of each morphotype in popula- tions reared under the various treatments. The relative proportions of each morphotype within the whole population differ except for BC and FE which
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TABLE IV
The relative frequency (%) of each morphotype in populations stocked at three densities, reared under two management procedures
Prawn density 5,000 ha-’ 10,000 ha-’ 15,000 ha-’
Group* A B A B A B
Small males 12 10 22 22 14 14 22 30 20 26 24 26 16 12 20
8 10 18 34 30 24
Average* * 16.3 f 7.6a 21.2 f 7.la.b 18.0 f 7.2a*b
Grange claw 32 24 males 18 26
32 24
Average 26.0 i 4.gb
32 26 24 24 14 24 16 22
22.7 i 5.3b
38 30 24 36 14 28 16
26.6 + 8Jb
Blue claw 6 4 males 6 8
8 8
Average 6.7 f 1.5c 10.0 f 3.2c 7.1 + 4.9c
10 10 8 8
12 16 10
4
6 2 2 16
12 8 4
Females 46 52 34 36 40 46 40 26 40 28 50 20 44 50 48 52 50 38
32 44 44
Average 43.3 f 8.8d 39.2 f 7.7d 40.8 c 9.4d
Females with 4 10 2 6 2 8 eggs 14 10 8 16 0 2
0 12 6 8 0 8
8 6 6
Average 7.7 f 4.5c 7.2 + 4.Bc 4.6 * 3.0e
*Group A = Tilapia: 7,500 ha-‘, feed: sorghum pellets, daily manuring; Group B = Tilapia: 3,000 ha-‘, Feed: carp pellets, weekly manuring; each number represents a single pond within each treatment. **Index letters indicate statistical significance of differences in relative frequency of mor- photypes. Values bearing the same index letter do not show a significant difference at the level of 01 = 0.05.
6’7
TABLE V
The average weight (in g) of each morphotype in populations stocked at three densities, reared under two management procedures
Brawn density 5,000 ha-’ 10,000 ha-’ 15,000 ha-’
Group* A B A B A B
Small males 29.83 37.20 30.00 22.00 19.43 9.29 33.00 24.93 20.70 21.77 10.92 14.50 14.75 14.83 10.10 14.20 26.71 12.00
23.18 15.93 15.92
Average* * 25.6 f 8.7a,b 21.9 + 4.7c 13.2 f 3.4d
Orange claw 50.19 57.92 47.56 46.46 40.47 38.13 males 45.89 50.38 46.17 44.50 32.25 48.50
40.69 47.43 37.86 42.67 40.17 41.64
52.67 31.25 38.45
Average 47.9 * 5.7e 45.4 ?: 4.2e 38.6 f 5.4d
Blue claw 69.00 75.00 54.20 65.80 45.33 57.00 males 59.00 65.00 55.75 58.60 38.00 51.62
82.00 46.50 53.50 58.50 53.37 65.00
77.67 38.00 49.50
Average 68.1 f 8.4f 57.9 f 9.2s 49.8 + 9.2e
Females 35.87 31.69 28.53 31.50 27.60 28.54 25.10 26.50 26.91 24.08 33.38 30.40
26.50 27.23
Average 30.7 + 3.2a 27.5 i 2.4a
Females with 39.50 43.60 40.00 41.67 eggs 41.57 44.60 41.25 37.37
- 33.00 44.25 -
40.25 37.67
Average 42.7 * 1.9e*d 38.7 i: 2.8d
23.60 21.86 18.32 24.70 22.42 24.43 22.53
22.5 i 2.0b
32.00 39.50 - 30.00
30.33 30.75 29.67
32.0 f 3.4a
*Group A = Tilapia: 7,500 ha-‘, feed: sorghum pellets, daily manuring; Group B = Tilapia: 3,000 ha-‘, Feed: carp pellets, weekly manuring; each number represents a single pond within each treatment. **Index letters indicate statistical significance of differences in average weight of mor- photypes. Values bearing the same index letter do not show a significant difference at the level of (Y = 0.05.
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TABLE VI
The average body length (in cm) of each morphotype in populations stocked at three densities, reared under two management procedures
Brawn density 5,000 ha-’ 10,000 ha-’ 15,000 ha-’
Group* A B A B A B
Small males 10.2 10.8 10.2 9.1 8.1 7.0 10.5 9.6 9.1 8.8 7.4 7.7
8.1 7.6 7.2 8.1 10.2 7.6
8.2 8.0 8.2
Average* * 9.5 + 1.1c.d 9.0 f O.gd 7.6 f 0.4e
Orange claw 12.1 12.6 11.8 12.9 11.2 11.1 males 11.5 12.3 11.7 11.8 10.5 12.5
11.6 11.8 11.1 11.7 11.7 11.3
12.2 10.4 11.4
Average 12.0 r 0.4a9b 11.9 f 0.4aJJ 11.1 f 0.6b
Blue claw 12.3 12.7 11.9 13.1 10.8 11.5 males 11.9 12.5 11.7 12.1 10.5 12.3
12.1 11.3 11.7 13.0 12.5 12.5
13.0 10.2 11.7
Average 12.4 jl 0.4a 12.2 f 0.6a 11.3 f O.gb
Females 11.0 10.7 9.9 10.8 9.5 9.6 9.9 10.8 10.0 10.1 9.0 10.3
10.1 9.8 9.6 11.0 10.7 10.0
10.1 9.7 10.3
Average 10.6 + 0.4c 10.2 f o.3c 9.7 f 0.3d
Females with 11.5 11.8 11.0 11.5 10.5 11.1 eggs 11.3 11.8 11.4 11.1 - 11.0
- 10.4 10.7 11.6 - 10.2
11.0 10.3 11.2
Average 11.6 c 0.2b 11.1 + 0.3b 10.6 f 0.3’
*Group A = TiZapia: 7,500 ha-l, feed: sorghum pellets, daily manuring; Group B=TiZupia: 3,000 ha-‘, Feed: carp pellets, weekly manuring; each number represents a single pond within each treatment. **Index letters indicate statistical significance of differences in average body length of morphotypes. Values bearing the same index letter do not show a significant difference at the level of 01 = 0.05.
69
TABLE VII
Claw length to body length ratio of each morphotype in populations stocked at three densities, reared under two management procedures
Prawn density 5,000 ha-l 10,000 ha-’ 15,000 ha-’
Group*
Small males
A B
0.72 0.31 0.88 0.29 0.27 0.41
Average** 0.48 i: 0.23d
A B
0.50 0.53 0.56 0.54 0.46 0.36 0.72 0.59
0.53 f O.lOd
A B
0.73 0.61 0.69 0.41 0.58 0.58 0.39
0.57 + 0.12d
Orange claw 1.06 1.07 1.04 0.86 1.08 0.97 males 1.05 0.89 1.03 1.05 1.03 1.04
0.95 1.02 0.97 0.95 0.97 1.02
1.04 1.00 0.94
Average 0.99 f 0.07h 0.99 f 0.06b 1.01 f 0.04h
Blue claw 1.88 1.86 1.81 1.60 1.81 1.88 males 1.56 1.71 1.59 1.85 1.52 1.50
1.66 1.73 1.78 1.74 1.81 1.82
1.62 1.70 1.41
Average 1.74 f 0.10a 1.68 f 0.14a 1.71 + 0.14a
Females 0.85 0.78 0.78 0.57 0.85 0.77 0.80 0.59 0.72 0.81 0.68 0.71 0.66 0.77 0.75 0.76 0.67 0.74
0.70 0.72 0.75
Average 0.74 * o.ogc 0.72 f 0.07c 0.71 * 0.05c
Females with 0.41 0.87 0.93 0.62 0.86 0.65 eggs 0.87 0.72 0.87 0.82 - 0.73
- 0.84 0.57 - 0.80
0.86 0.89 0.88
Average 0.75 f O.lSc 0.83 i 0.09’= 0.75 f O.llC
*Group A = Tilapia: 7,500 ha-l, feed: sorghum pellets, daily manuring; Group B = Tilapia: 3,000 ha-‘, Feed: carp pellets, weekly manuring; each number represents a single pond within each treatment. **Index letters indicate statistical significance of differences in claw length to body length ratio of morphotypes. Values bearing the same index letter do not show a signifi- cant difference at the level of Q = 0.05.
70
occur at similar frequencies. The proportion of morphotypes within the populations were: 18 SM; 25 OC; 8 BC; 41 F; 8 FE. This proportion was not affected by stocking density. An exception to this rule was found in the case of gravid females which demonstrated a significant decrease in their relative frequency at the highest stocking density (15,000 ha-‘). This may be attrib- uted to the fact that the average growth of females was lower at the highest density; thus, fewer females would have reached the minimum size required for sexual maturation during the growout period of 90 days.
Table V presents the average growth of each morphotype in the various treatment groups. The average weight was significantly different for the vari- ous morphotypes under any given prawn density but was independent of Tilapia stocking rate. The strongest response to stocking density was that of the BC males, which had reached an average weight of 68.1 g at the lowest density (5,000 ha-l) and only 49.8 g at the highest density (15,000 ha-‘), irrespective of Tilapia stocking and feeding strategy. The size ranking of each morphotype was not affected by prawn density.
Table VI presents the effect of the various treatments on the average body length of each morphotype. Body length was not significantly different be- tween OC and BC and, in general, was much less sensitive to the changes in initial prawn stocking density. The difference observed between OC and BC males in average weights can be attributed to the large chelates characterizing the BC males, which constitute about 20% of their total body weight. In general, body length is not an accurate parameter of growth, especially for animals weighing more than 30 g. From this stage, further growth contrib- utes more to the thickness of the body rather than to its length.
Table VII presents the relative claw length of each morphotype in popula- tions reared under various conditions. The relative claw length, as measured by the ratio of claw length to body length and which reflects the social role of each male morphotype (Ra’anan, 1982; Ra’anan and Cohen, in prepara- tion), was significantly different for each of the three male morphotypes and between the males and the females. However, no difference was found between females and gravid females. This ratio is constant for each morpho- type and is independent of either prawn or Tilapia density.
To summarize, density dependent parameters include (a) the average growth rate as measured by final average weight and by body length and (b) the relative frequency of gravid females. Both are inversely related to dens- ity. In all cases, increased Tilapia density and modified feeding-manuring strategy had no influence on prawn yields and on parameters of the social structure of M. rosenbergii.
ACKNOWLEDGEMENTS
The authors thank Dr. G. Wolfarth and Dr. G. Hulata for enabling the stocking of prawns in the experimental fish ponds and for their valuable ad- vice. Thanks are also due to Mr. Moshe Amir and the staff of ‘Do? Station
71
for ensuring proper management of the ponds. We appreciate the asssistance of Dr. Tom Brody and Prof. Moshe Soler in the analysis of the results and of Mr. Ben-Zion Rubinfeld for his involvement in data collection. Special thanks are given to Aquaculture Production Technology (Israel), Ltd., which helped to finance the study.
REFERENCES
Baissac, P. de B., 1976. Problems caused by the occurrence of the filamentous algae, Spirogyra sp., in culture ponds of Macrobrachium rosenbergii (de Man) in Mauritius. Rev. Agric. Suer. Ille Maurice, 53: 206-211.
Barnes, A., 1980. Aquaculture of the freshwater prawn Macrobrachium rosenbergii in Is- rael: Ecological dynamics of growout ponds and its effect on the yields and popula- tion structure. M.Sc. thesis, submitted to the Life Science Institute, The Hebrew Uni- versity of Jerusalem, 68 pp.
Brody, T., Cohen, D., Barnes, A. and Spector, A., 1980. Yield characteristics of the prawn Macrobrachium rosenbergii in temperate zone aquaculture. Aquaculture, 21: 375-386.
Cohen, D., Ra’anan, Z. and Brody, T., 1983. Population profile development and mor- photypic differentiation in the giant freshwater prawn Macrobrachium rosenbergii (de .Man). Proc. World Maricult. Sot., 12: (in press).
Cohen, D., Ra’anan, Z. and Barnes, A., 1983. Production of the freshwater prawn Macro- brachium rosenbergii in Israel. I. Integration into fish polyculture systems. Aquacul- ture, 31: 67-76.
Frankenberg, D. and Smith, K.L., 1967. Coprophagy in marine animals. Limnol. Oceano- gr., 12: 443-450.
Malecha, S.R., Buck, D.H., Baur, R.J. and Onizuka, D.R., 1981. Polyculture of the fresh- water prawn, Macrobrachium rosenbergii, Chinese and common Carps in ponds en- riched with swine manure. I. Initial trials. Aquaculture, 25: 101-116.
Moav, R., Wohlfarth, G., Schroeder, G.L., Hulata, G. and Barash, H., 1977. Intensive polyculture of fish in freshwater ponds. I. Substitution of expensive feeds by liquid cow manure. Aquaculture, 10: 25-43.
Nie, N.H., Hull, C.H., Jenkins, J.G. and Steinbrenner, K., 1971. SPSS, ANOVA, ONE- WAY-RANGES, LSD-test. In: K.J. Bowmen and M. Cahill (Editors), SPSS, 2nd edi- tion. McGraw-Hill Book Company, New York, pp. 425-430.
Ra’anan, Z., 1982. The ontogeny of social structure in the freshwater prawn Macro- brachium rosenbergii (de Man). Ph.D. dissertation, submitted to the Life Science Insti- tute, The Hebrew University of Jerusalem, 109 pp.
Shang, Y.C., 1981. Freshwater prawn (Macrobrachium rosenbergii) production in Hawaii: Practices and economics. Sea Grant Miscellaneous Report UNIHI-SEAGRANT-MR-81- 07. Aquaculture Development Program, Department of Land and Natural Resources, State of Hawaii.
Smith, T.I.J., Sandifer, P.A. and Smith, M.H., 1978. Population structure of Malaysian prawns, Macrobrachium rosenbergii (de Man), reared in earthen ponds in South Caro- lina, 1974-1976. Proc. World Maricult. Sot., 9: 21-38.
Tang, Y.A., 1970. Evaluation of balance between fishes and available fish foods in multi- species fish culture ponds in Taiwan. Trans. Am. Fish Sot., 99: 708-718.
Wang, J.K., Huang, W.Y. and Fujimura, T., 1975. Some characteristics of earthen pond prawn production in Hawaii. Working Paper No. 10, Sea Grant College Program, Uni- versity of Hawaii, Honolulu, 20 pp.
