A CRITICAL EXAMINATION OF THE EVIDENCEFOR PHYSICAL AND CHEMICAL IN-FLUENCES ON FrSH MIGRATION.*

BY F. E. CHIDESTER, A.M., PhD., Professor of Zoology,University of West Virginia, Morgantown, West Virginia.

{From the Woods Hole Laboratory of the t/.S. Bureau of Fisheries.)

C O N T E N T S

i. Introduction2. Parent Streams . . . .3. External Influences—

a. Physical—Character of the BottomStream PressureLights and Shadows .Temperature

b. Chemical—Food . . . .Salinity, Osmotic Pressure

I.

TAG*

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3-

4-

c.J

f.

External Influences—contd.b. Chemical—contd.

Acidity or Alkalinity. Hy-drogen-ion Concentration

Pollutions . . . .Internal Influences —

SensesPhysical Condition of the BodyChemical Conditions

General Conclusions .Rpferennea . .

Introduction.

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100104107

108

IT was because of a series of records prepared in connectionwith a study of the salt-water minnows that so successfullycope with the salt-marsh mosquitoes of the north (Chidester,1916) that the writer was invited in 1919 by the U.S.Commissioner of Fisheries, Dr H. M. Smith, to engage inan attempt at the physics and chemistry of the migrationsof fish.

The subject is one that several experienced zoologists haverefused to follow for any length of time, as it is difficult offield observation, and certainly not one to be solved bylaboratory experiments.

After several summers of spare time spent in experimentalwork, amplified by field observations, it has been deemed

* deceived January 30th, 1924.79

F. E. Chidesteradvisable to survey the literature, and this paper will, it ishoped, aid in crystallising our knowledge of the migrations ofanadromous fishes.

2. Parent Streams.

To a zoologist who is looking for a problem that willeventually have a solution, it is most disconcerting to discoverthat there is much evidence that fish like the salmon are ableto return in an apparently inexplicable manner to the streamswhere they were bred.

We are deeply indebted to Dr C. H. Gilbert of StanfordUniversity for most careful work on fish scales that has shownthat salmon return to the river of their nativity for spawning,and that they are even able to locate in that river the spotwhere they were once fingerlings.

Jordan mentions certain observations of Dr Gilbert on theChinook salmon and Red salmon of the streams near WallaWalla, Washington. Dr Gilbert found that at a point wherethe salmon have a choice of two streams that come togetherunder a bridge, the Chinooks (king salmon) go up either oneof the streams indiscriminately, but the Red salmon (bluebacks)turn always to the stream with a lake.

In a recent paper Dr E. E. Prince, Dominion Commissionerof Fisheries, Ottawa, Canada, states (1916) that his previousreport—published in 1896 and repeated in 1912—to the effectthat "each river has its own race of salmon," is borne out bymore recent observations. A dark-fleshed race of Sockeyesalmon inhabit a small creek near the Skeena River, and thesalmon canners rarely net them as the meat is of a " dark,repulsive colour," although the distance is not great from thewaters that furnish the attractive pink salmon of the regularcatch.

Dr David Starr Jordan is inclined to question whethermigration up the parent streams may not be due to the factthat the young fish do not travel far from the mouths of therivers that gave them birth, and consequently they find theparent waters pouring into the ocean and quite naturallyreturn to them. Jordan also believes that the salmon are notunfailingly true to their native rivers.

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Examination of Influences on Fish MigrationJordan has pointed out the fact that salmon do not

apparently care about the quality of the water, and that whilethe Chilcoot River comes from a glacier and the water is milkwhite with glacial debris, the fish migrate into it. Jordan(1920) also cites a case of apparent attractiveness of lakewater.

The first lake on the Yukon River, Lake Labarge, is1800 miles from the mouth of the river. At Boca de Quadra,also a noted salmon stream, is a little stream about ten feetwide and less than a mile long, the outlet of a lake. At thehead of the lake it is fed by clear springs. The fish go up thesmall stream just as they go up the Yukon, although they haveonly about five miles to go. Their start is accordingly a lateone. Jordan does not explain this condition.

Further interest in lake-fed streams is aroused when wecite the case (mentioned by Jordan) of observations byJ. P. Babcock of the British Columbia Fish Commission(Jordan, 1919). Babcock observed that in the case of waterpiped from a lake-fed stream across to another stream, the Redsalmon gathered around the mouth of the pipe which containedthe lake water.

The writer cannot refrain from remarking at this juncturethat a fish responds to currents of water, and that it is quitelikely that the Red salmon would have gathered around almostany non-poisonous fluid of the optimum temperature, providingit came with a little force through a tube.

Our knowledge of salmon behaviour has been clearly statedby Dr C. H. Gilbert in a personal letter, in which he answersseveral questions asked by the writer, and with his permissionthe answers will be quoted.

" Professor F. E. CHIDESTEE," West Virginia University,

" Morgantown, W. Va.

"STANFORD UNIVERSITY, CALIFORNIA,

" irdJanuary 1923.

" DEAR SIR,—I have no knowledge concerning possible factors governingmigrations of fishes, and am thus unable to prepare any discussion of thesubject that you may care to use. As regards migration of the salmon,however, there are certain unquestioned facts that must be taken adequatelyinto account by any theory which claims to explain their movements.

" 1 . Salmon which are schooling together in the sea on feeding groundsVOL. 11.—NO. 1. 81 F

F. E. Chidesterfar removed from their final spawning districts, will at the proper time separateand go their own way rather directly to the mouth of the distant stream fromwhich they originated. At the time they separate, it would seem they mustassuredly be exposed to identical environmental conditions.

" 2. Salmon ascending a river together will react differently on approach-ing a given tributary, though again it would seem they must be exposed to thesame conditions. There is a fair body of evidence to show that in the mainthey will re-enter the tributary in which they were hatched.

" 3 . In both the above instances, we seem wholly at a loss to suggest anypurely external factors which condition and guide the migration, and yet leadto such diverse results when applied to fish of different early history.

"4. The 'parent-stream theory,' in so far as it has validity, is not a theoryin any sense of the term, but a bald statement of fact. The salmon either do,or they do not, return in the main to their parent stream at maturity. Wehold that they do, but we are far from claiming that this phrase, which ismerely descriptive of their conduct, affords any explanation of it When thequest is for the causative factors of migration, the 'parent-stream theory' isa confession of ignorance pure and simple. But it seems far more whole-some and more hopeful of future results to confess ignorance where ignoranceundoubtedly exists, than to set up spurious claims to achievement, as is all toofrequently done in this field.—Very truly yours, C. H. GILBERT."

Such clean cut statements as these backed by the observa-tions of Dr Gilbert and his associates, Mr Henry O'Malleyand Mr W. H. Rich (1919), who tagged adult Sockeye salmonand studied their migration, would seem to indicate that wehave a long way to go in explaining the factors that influencemigration.

It may be that we shall have to come to the idea of emana-tions from the mother, transmitted to the offspring, whichserve to guide the fish of a particular race back to theirparent stream.

It may not be out of place at this juncture to mentionthe statement of J. O. Snyder, who reported on the return ofking salmon (1922).

In 1919, 2500 king salmon were marked by removing theadipose and the right ventral fins. They were expected toreturn to the Klamath River in 1921, on the basis of previousscale data. At that time twenty-three were recaptured. Theage calculated from the scales was identical with the knownage. The interpretation given is that the fish remained inthe river during the first year, and most of them must havebeen in contact with the same environmental conditions of

82

Examination of Influences on Fish Migrationthe sea during the second year. Snyder concludes thatassociations of individuals formed in youth may continuethroughout life.

The remaining discussion will instance experiments andobservations that show some advance in our knowledge ofthe determining factors that may in some way influence themigrations of fish.

3. External Influences.

a. Physical— Character of the Bottom.—The anadromousfishes migrate past all sorts of obstacles and over bottoms ofvarious types in order to reach favourable spawning grounds.

It is the belief of Gurley (1902) that the selection ofspawning grounds is by no means a question of chance, b'uthas been determined by the egg type "via natural selection."Gurley mentions the fact that spawning grounds of fishesare mainly of three kinds : mud, weeds and sand, gravel androck, and that the habits of the fishes in deposition and thephysical condition of the eggs have determined the survivalof the fishes. One is immediately led to inquire whether themigratory fish do not occasionally become dispersed to newfavourable localities for spawning and thereafter establish arace for that particular stream. We must have furtherobservations and records to fully substantiate this statementso frequently given as a fact.

Prince has stated (1920) that the eggs and young ofbut few fishes are found on the sea bottom, and that themajority of marine fishes deposit floating eggs or else spawninshore. He cites the work of Professor M'lntosh ofSt Andrews, Scotland, who proved that the eggs* of thesalmon will not develop in salt water, but become rubberyin consistency.

The migration of fishes seems to be unaffected by thecharacter of the bottom, but their spawning places are quitecertainly regulated by such factors. Observations of pollutedstreams prove, however, that fish will spawn in places thatwere formerly clean but have become so polluted that theeggs are not able to develop.

Stream Pressure.—There is no question that the factor83

F. E. Chidesterof stream pressure is extremely important in connection withthe migrations of fish.

Chamberlain (1907) writes of the tendency in dry seasonsof salmon to tarry inshore in bays and the mouths of smallstreams, and only to proceed up to their spawning groundswhen the floods have come rushing down.

Prince (1920) mentions the importance of a down-floatingstream, but emphasises the necessity for shallow, clean, gravellyrapids in the case of the salmon, and gives weight to theadded fact that the cold waters of the salmon rivers areusually well aerated, since coldness increases the power ofthe water to absorb gases. Further mention will be madeof both of these points.

The significant experiments of E. P. Lyon (1904, 1909)performed with the killifish, Funduhis heteroclitus, Linn., thescup, Stenotomus chrysops, Linn., the stickleback, Gasterostezisbispinosus, Walb., and the butterfish, Poronohis tricanthus,Peck., indicate clearly that fish respond to stream pressurethrough the optic and tactile senses.

By an ingenious series of devices, Lyon proved that thefish Fundulus responds to relative motion rather than toa current; that the moving "optical field" is the stimulus,and that in the complete absence of pressure the fish willrespond to movement outside glass containers. He concludedthat the current only stimulates by moving the fish awayfrom their environment.

Blinded fish on the bottom of a long box with open ends(screened with coarse netting) oriented themselves in the sand.Other fish that were blinded and placed in the tideway leadingfrom the eel-pond at Woods Hole, Mass., were quite irregularin their motion until they touched the bottom and then theyheaded upstream. Even contact with a bit of eel-grass wasenough to give them orientation.

The general cutaneous nerves were the ones involved.Dr Caswell Grave has emphasised to the writer the

supposition that variation in turbidity of the water maytherefore be a most important difference in the orientationof the fish to streams, and that debris in the water at thetime of floods will serve to accentuate tactile stimuli.

84

Examination of Influences on Fish MigrationLyon showed that in the case of concentrated streams

such as those from a small bore tube or flume, there issufficient difference in the velocity of the water at the centreand the outside of the stream to furnish the requisite stimuli.In his experiments with fish blinded in one eye, Lyon proved(1909) that they react to currents like the normal fish.

The writer found in 1919 and 1920 (Chidester, 1922)that by increasing the stream pressure of fresh water or oftoxic substances in solution and presenting them in a troughthat was almost parallel to its twin with sea water flowinginto a long receiving trough, it was possible to lure killifish(Fundulus heteroclitus, Linn.) into the unfavourable stream.It is quite possible that the idea of intoxication by chemicals,suggested by Shelford, is not always tenable, and thatoccasionally the fish in his experimental tank moved towardsthe toxic substances because they were attracted by theforce of the entering stream. His control and experimentalstreams were situated at opposite ends of the tank, with theoutlet at the middle.

It must of course be recognised that the factors oftemperature and oxygen content of the water are significant,but we must also appreciate the fact that just as birds respondto air currents, fish not primarily confined to the bottomrespond most definitely to the force of moving water.

As pointed out so aptly by Lyon (1904) the fish in rushingtorrents orient because of the difference in velocity of theadjacent parts of the stream. In the wider and deeperstreams, sight or contact with the bottom or with floatingparticles in the water furnish the requisite nerve-stimuli.

Rutter (1902) has shown that the Chinook salmon runinto the rivers against ebb tide, and then, when the tideturns, run out against flood tide. The flood tide is notcontinuous for so long a time as the ebb tide, and so thefish keep ascending until the tidal movement is replaced bythe river current.

Nothing could be more striking or more worthy ofapplication to lessons on human behaviour than the fact thatweakened and spent salmon go down to the sea tail first,feebly fighting the current.

VOL. IL—NO. I. 85 F 2

F. E. ChidesterLights and Shadows.—Fish vary considerably in their

movements according to light or to darkness. Salmon moveboth by night and by day. Atkins (1874) mentions the factthat the Atlantic coast salmon spawned at night or on adark cloudy day. Alewives rest in small pools at night andtravel by daylight. Herrings apparently require clear waterand a clear sky for their migratory movements.

Shad are said to be timid and easily frightened by shadows.M'Donald cites the case (1884) of the shad, and indicates thatfloods and muddy water arrest their movements.

Allen, in discussing the migration of mackerel {Mackereland Sunshine, Allen, 1909), has pointed out that sunshineproduces more of the plant food of Copepoda, such as diatomsand Peridinidse, and that an abundance of Copepoda offers richfood for the mackerel. He attempted, therefore, to "correlatethe average quantity of mackerel per fishing boat taken in Maywith the total number of hours of sunshine recorded duringthe first quarter of the year." The effort was unsuccessful,however, and he states that "whilst the 1905 temperaturemaximum agrees with the maximum total catch of mackerelthe temperature of 1903 is accompanied by low catches ofmackerel." Fishermen of the Atlantic coast find that theyare more successful in catching mackerel on dark days, andaccording to Mr Ernest Romling of the U.S. Bureau ofFisheries, they believe that this is due to the fact that theirscattered bait (chum) is present in the absence of the livingCrustacea that appear near the surface on bright days.

Reeves has concluded (1919) that the longer wave lengthsof light have a physiological or psychological effect uponsunfish {Eupotnotisgibbosus, Linn.) and horned-dace {Semotilusatromaculatus, Mitchill) that differs considerably from light ofshorter wave length and from white light.

The fish in her experiments were trained to respond to foodstimulus with the accompaniment of blue light. Then itwas tried with red light of brightness approximating that ofthe blue for the human dark adapted eye. The fish respondedabout as often to red as to blue at first and then becamediscriminating and red had to be reduced in intensity.

Parker and Larchner studied the responses of Fundulus86

Examination of Influences on Fish Migrationto white, black, and darkness (1922). They prepared threeboxes, one lined with dull white paper and exposed to the lightfrom a 100 watt lamp: the second lined with black paper andsimilarly exposed to the 100 watt light: and a third, absolutelylight-proof. Funduli placed in the light one remained light incolour ; those placed in the dark one remained dark in colour;but the ones in the light-proof box remained light until removedand then became dark for five minutes, later becoming lightagain. Temporarily blinded fish also remained light coloured.These experiments, while of no special interest in connectionwith the problem of fish migration, serve to emphasise theoptical factor in behaviour, and to corroborate the work ofSumner and of Mast along the same line.

The writer has shown (Chidester, 1923) that Fundulusheteroclitus, Linn., when given a choice of temperature andlight combinations, is influenced somewhat by the attractivenessof intense light, and may be attracted towards water that isseveral degrees warmer than that which is its optimum atthat time, without the added factor of light.

We must conclude that fish vary in their responses to lightso much that it can be stated that some are primarily influencedin their reaction to currents by their optical sense, whileothers are primarily responsive to turbidity and to powerfulstream pressure increased by floating debris.

Temperature.—By far the most evidence has been gatheredto support the theory that temperature is the primary influencein fish migration.

Gurley (1902) has prepared a highly instructive paperdiscussing the relations between temperature and the otherfactors in fish migration. He holds that there is probablya temperature-responsive nerve-mechanism. This mechanismwould explain why spawning in cooling water is associatedwith migration from warmer to cooler water.

Gurley points out that the time of spawning has beendetermined by natural selection, and that natural selection hastherefore determined the time of migration.

To his statement that spring spawning does not necessarilymean spawning in warmer water, the writer most heartilysubscribes. In connection with observations on the killifishes

87

F. E. Chidesterof New Jersey (Chidester, 1920), it was observed that theearly spring migrants to the marshes came in April whenthe waters inshore were cooler than they were at the time inthe Raritan Bay.

Jordan says {Science Sketches, 1888, pp. 51-52) that Blue-back salmon and Humpback salmon ascend only snow-fedstreams with sufficient volume to send their waters well outto sea. Gurley adds to this the statement that spring freshetsmean heavy spring runs and lighter fall runs. Gurley believesmost salmonids to be spawners in cooler water. He statesthat migration to cooler water favours the development of thegonads. Gurley has also pointed out that the fish probablystarts to migrate as the result of a temperature stimulus, thencontinues in response to the pressure stimulus from currents,and that it runs upstream until the gonads have ripenedtheir products and spawning takes place.

Natural selection is the factor that determines the survivalof eggs spawned in water of a certain character.

Chamberlain claims (1907) that fish leave cooler water forwarmer. He also points out that streams with lakes have ahigher temperature in the summer than streams of similarvolume without lakes. Certainly in the case of some fish suchas the menhaden it would seem that they prefer warmer watersoffshore in the summer. They are attracted by water aboveio° C , and may even migrate inland until the water reaches atemperature of 23° C. (Goode, 1879).

Stevenson (U.S. Fisheries Report, 1898) quotes M'Donaldas stating that "warm rains produce vast schools of shad."Floods and muddy water arrest their movements, however.

Mr R. A. Goffin and Mr W. L. Howes of the Woods HoleLaboratory of the Bureau of Fisheries record the fact thatalewives come into Oyster Pond soon after the ice leaves in thespring when the temperature is not more than 50 C. The swiftcurrents flowing out of the pond cause the fish to rush in greatshoals and almost fill the stream. They are travelling fromwarmer to cooler water.

Shelford and Powers showed (1915) that herring aresensitive to temperature differences as small as o.2°C.

Galtsoff (1923) in a paper on the migration of mackerel in88

Examination of Influences on Fish Migrationthe Black Sea shows that as the temperature decreases the fishpress inshore. They are caught in horizontal nets close tothe shore. Apparently the fish are not affected by absolutetemperature but by the relative temperatures. The samephenomenon occurs when the temperature drops from 24° C. to2i°C. as happens in the drop from \f C. to io°C, as observednear Sebastopol. Galtsoff holds that the difference in salinityis not significant, as the same phenomenon occurs in regions ofthe Black Sea with quite different content of salts.

Johnstone (1908) concludes that it is difficult to separatethe influences of salinity and temperature, but there is nodoubt that temperature is a factor in itself.

He believes that there is sufficient evidence to concludethat seasonal migrations of fish are related to seasonal changesin temperature, and cites the work of D'Arcy Thompson, whohas correlated the volume of catches made by Aberdeentrawlers with the temperature of the sea on the fishinggrounds.

Ward (1920) discusses the migration of the Sockeye salmonand finds that the volume and the swiftness of the streamsare not apparently determining factors in the selection of onetributary to a stream in preference to another. He furthershows that great difference in turbidity is ineffective, andthat there is no difference in the apparent chemical characterof the waters. The food supply is apparently uniformly poor.

Temperature is the factor that he believes of paramountimportance, and he subscribes to the theory that the salmonprefers steadily flowing cool water for spawning.

Whatever influences may be important for migration besidestemperature, the writer holds that we must acknowledge thefact that it bears a most important relation to chemicalprocesses, and thus involves not only the environment of thefish but the metabolism of the body of the animal itself. Evenif we decide that the fish has some mysterious sense that mancannot discover, it is quite evident that the temperature of thewater will have a pronounced effect on the utilisation of thatsense.

b. Chemical—Food.—Fish vary considerably in their habitsas respects feeding when they migrate inshore.

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F. E. ChidesterYoung immature fish continually travel from the deep

waters of the ocean to the shallower waters of the coast andup into the marshes in search of food. Although severalspecies may be in the same shoal, in general it is found thatthose travelling together far into the inland streams duringthe period prior to maturity are of the same species. In theocean the young of several species will be found together.

At the same time that immature minnows come to feed onthe teeming insect life of the salt marshes (Chidester, 1916,1920), one notes that older fish of the same species aremigrating inshore primarily for the purpose of spawning.

During the period of travel from the deeper waters, thereis usually little feeding done by the mature animals that areto spawn in brackish or fresh water. In no fishes is thischaracteristic more striking than in the salmon.

Gurley (1902) believes, and it would seem rightly so, thatabstinence from food in fishes is in direct ratio to the length oftime required as a minimum and the amount of time availableas a maximum, for the species to reach their spawning grounds.

Prince holds (1920) that the salmon has never changedits habits but " repairs to the ancestral breeding localities,regardless of the geological and topographical changes wroughtin the course of long centuries." He states that the surround-ings of the spawning beds have been changed and the formersalinity has been changed to freshwater conditions ; but theconnecting channels still remain, and the salmon persists inits habit of going to the old spawning locality.

Whether we accept this as the explanation of the habitsof the salmon or not, we must acknowledge that the fishtravels for 2000 miles up the rivers of the Pacific Coast tospawn, and that it fasts during the period after it leaves theocean for fresh water.

Greene (1914) is responsible for a most careful study ofthe storage of fat in muscular tissue of the salmon. He foundthat the salmon do not feed in fresh water, no matter howfar they travel into it to spawn. The stored fat is apparentlythe only source of the fats to build up the ovaries, and italso must furnish the energy for muscular activity during thelong pilgrimage to suitable spawning grounds.

90

Examination of Influences on Fish MigrationIt is stated by other competent observers, however,

that certain salmon will seize bait while migrating up theColumbia River.

The explanation of the fact that a salmon will seize baitwhen migrating is probably that while the animal is toostrongly impelled towards its spawning grounds to stop forfeeding en route, it is quite responsive to the optical stimulusof something that is apparently edible.

In the case of fish that spawn inshore, such as the cod,it is stated by Mr R. Hamblin of the U.S. Fisheries Laboratoryat Woods Hole, Mass., that although the manuals of fish-culture indicate that they do not eat during the spawningseason, both the females and the males will eagerly seize foodplaced in their detention pools.

It is probably safe to conclude that fish that spawn inshorein salt water or brackish water will feed until just before theyare to spawn, while those that travel far inland press onward,responding by optical and tactile senses to current stimuli,until their eggs have matured and they must spawn. Thedistance which any particular race of fish travels beforespawning is in all likelihood determined by natural selection,together with the factor of time required for the developmentof the gonads.

Salinity, Osmotic Pressure.—It has been shown that theanadromous fishes have blood that is more saline in sea waterthan it is in fresh water. It has also been found that changingthe medium for marine fishes to a less saline one will inducechange in their blood. The internal equilibrium of the animalhas been preserved by the presence of membranes that arepractically impermeable to salts, though permeable to water.

Mather (1881) has listed thirty-three species of fishes thatcan live in both fresh and salt water. Slow acclimatisationpermits these animals to range between the two mediawith impunity.

There is great variation in the adaptability of fishes tosalt or fresh water, and this adaptability is probably due toan inherited resistance.

Sumner (1905, 1906) has studied the effects of changingcertain brackish and freshwater fishes to pure fresh water and

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F. E. Chidesterto water of different degrees of salinity. He mentions changingthe young of the Chinook salmon (Onchorhynchus tsawylscha)which weighed from 8 to 30 gms., and which had been rearedin fresh water, abruptly to water of a density of 1.013 withoutany harm, and suggests that a higher salinity would nothave injured them.

Rutter (1904) found that if the young of Pacific Coastsalmon were transferred alternately from sea water of low tohigh dilution, it was possible gradually to raise the salinity.This reminds us of the gradual change for the fish that mustresult when it travels with the ebb and flow of the tide beforeit finally begins the long journey in fresh water. Rutterfound that young quinnat salmon were able to live in highersalinities as they grew older, and from 25 per cent, seawater at six days of age they were able at two months to livein almost pure sea water.

The age of Fundulus heteroclitus embryos was found byLoeb (1894) t o De definitely correlated with their ability tosurvive the addition of different proportions of NaCl to seawater.

Bert (1871, 1873, 1883) found that he could graduallyacclimatise freshwater fishes to live in water of one-half thesalinity of the sea, and that they would survive abrupt transferto diluted sea water if the proportions were two parts distilledwater to one part of sea water. He explained the death offreshwater fishes in salt water by osmotic action on the gills,producing contraction of the capillaries and thus asphyxiation.With scaleless fishes, osmotic action took place over theentire surface of the body.

Fredericq (1885) indicated that the gills, while permeableto gases, are almost impermeable to salts of the sea.

Bert (1883) mentioned the fact that if mucus was removedfrom skins of freshwater eels, they were quite susceptible tosalt water.

Garrey (1905) experimented with Fundulus heteroclitus,denuding about one-half the body surface of scales from alarge number of them. When placed in fresh water, normalsea water, and a mixture of distilled water with an equalquantity of sea water, it was found that the fish survived in

92

Examination of Influences on Fish Migrationthe sea water of one-half its normal concentration, but diedin the other solutions. Garrey concluded that if the internaland the external media are approximately isotonic, no ill effectsresult. He holds that injury to the integument furnishesan opportunity for fatal osmotic action.

Sumner (1906) was not able to confirm Garrey's work.Trout and other freshwater fishes must be handled with

great care when stripped of their spawn.There must be considerable variation in the susceptibility

of fishes to injuries, as many salmon arrive at their spawninggrounds with bodies " torn by rough stones, gashed by juttingrocks, maimed by jagged and precipitous obstacles, or byfalling, time after time, down almost impassable falls " (Prince,1920).

Ringer (1883), working with minnows and goldfish, triedthe salts of sodium, potassium, and calcium to discover whichwere capable of sustaining life longer and found that CaCO8

would sustain life longer than a corresponding quantity ofsodium or potassium salts. Combinations of KC1, NasCOa,and CaCla aided materially in supporting life. When fish wereplaced in solutions in which many fish had previously died,the new lot lived as they gained from the organic salts thrownoff by the dead fish.

Loeb (1900, 1905, see 1915 for references) has introducedthe term physiologically balanced solutions, and defines themas solutions in which the toxic effects are annihilated, whicheach or certain of their constituents would have if they werealone in solution. He has pointed out that the specificinjurious action of NaCl, which destroys the impermeabilityor semi-impermeability of the membrane, may be counteractedby the addition of CaCl, or a mixture of KC1 plus CaCl2.

Temperature is a factor that influences the toxicity of salts.Loeb and Wasteneys (1912) made experiments with

Fundulus caught in January in L. I. Sound and kept thereafterin a laboratory at 10° C. The fish were changed to Ringer'ssolution and to sea-water, and it was found that the highesttemperature they could withstand was 33° C. and the highestconcentration was m/4. The higher the concentration of thesalts the more resistant the fish were to the higher temperature,

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F. E. Chidesterup to 330 C. Above that the resistance decreased. Onceimmunised against the higher temperature the fish withstoodtransfer to high salinity after being kept in an ice chest.

The authors make two suggestions by way of explanation.First, that rise in temperature brings about changes in thesurface of the cells of the body whereby the latter loses itsprotective impermeability. Second, that under the influenceof higher temperature a substance is formed that protectsagainst the effects of higher temperature. Formation of thissubstance is gradual. Thus the writers explain how animalsonce immunised against high temperature could be kept alive.

The osmotic pressure of the blood of fishes has engagedthe attention of numerous workers, including Fredericq, Mosso,Quinton, Rodier, Botazzi, Garrey, Sumner, and Scott.

As discussed by Scott (1913) the common method ofdetermining the osmotic pressure of a solution is by thedetermination of its freezing-point. The depression of thefreezing-point of the solution below that of pure water isproportional to the osmotic pressure of the solution. TheBeckman thermometer is commonly used to determine thefreezing-point depression or A.

Fredericq (1885 et seq) showed that the osmotic pressureof both elasmobranchs and teleosts was about one-half thatof sea water, while the blood of marine invertebrates wasnearly isotonic with their medium.

Bottazzi (1896, 1897, 1901) used the cryoscopic method ofdetermining the freezing-point of the solution and then theosmotic pressure, and his results were in accord with thoseof Fredericq.

Rodier (1899, 1900) and Garrey (1905) have confirmedthe results of Bottazzi on teleosts and elasmobranchs.

Garrey found (1905) the freezing-point of the blood ofteleosts to have a mean value of —0.872° C, while the meanvalue of that of the blood of the elasmobranchs of the WoodsHole region was — 1.92° C. The value of A for the sea waterwas approximately — 1.820 C.

Greene found (1904) that the freezing-point of salmon bloodwas for sea salmon, — 0.762° C. ; for brackish water salmon,— 0.737° C. ; and for spawning ground salmon, — o.628°C.

94

Examination of Influences on Fish MigrationThis decrease is 3.3 per cent, for the brackish water salmonand 17.6 per cent, for .the spawning ground salmon. Thiswork is significant as it indicates the independence in relationbetween the water and the blood-composition for the salmon.Greene is not disposed to ascribe the fall of concentrationof the blood of 17.6 per cent, to direct absorption of waterin fresh water, but to place much weight on the fact thatthe animals are from eight to twelve weeks in fresh waterwithout food.

Dakin (1908) found that the freezing-point of the bloodof the flounder, Pleuronectes flesus, in the North Sea was0.830 C , while in the River Elbe in fresh water its blood hada freezing-point of o.68°C, a decrease of 15 per cent.

Scott (1916), from whom many of the references in thissection were obtained, studied the freezing-point of the bloodof the white perch, Morone americana, which lives equallywell in fresh or in salt water. When taken from TashmooPond, Marthas Vineyard, the blood showed a A of o.635°C.The water was slightly brackish. After remaining in runningtap-water for a day, perch from this same pond were examinedand their blood showed a A of 0.571 ° C , similar to sea water.Still others were placed in sea water for two days and the Aof their blood was 0.7660 C.

Scott concludes (1916) that anadromous fish are "able toadapt themselves to a degree to the great changes in theosmotic pressures of the external medium, which they meet inpassing from salt to fresh water, or vice versa, by a slightcorresponding change in the osmotic pressure of the blood."

Wells has shown (1915) that starvation may cause certainfishes to seek water of lower concentration of salts and othersto seek water of higher concentration of salts. Possibly thismay be correlated with the migration of some of the anadromousfishes back to the ocean after spawning. It does not, of course,explain their journey to the fresh water to spawn.

The work of Shelford and of Wells indicates that fishes areprobably not so sensitive to salt ions as they are to hydrogenand hydroxyl ions.

Acidity or Alkalinity. Hydrogen - ion Concentration.—Wells showed (1915) that freshwater fishes select slight

95

F. E. Chidesteracidity in a gradient, when the other choices are neutralityor alkalinity.

Shelford and Powers demonstrated (1915) that alkalinityand acidity are more important in the behaviour of the herringthan is salinity.

Moore, Prideaux, and Herdman showed (1915) that thehydrogen-ion concentration (carbon dioxide tension) of seawater is subject to seasonal variation. So far investigationsof such seasonal change in freshwater streams have not beenpublished.

M'Clendon showed (1916) that changing the PH very muchkilled marine animals more quickly than changed salinity.

Shelford (1918, 1918a) has emphasised the toxicity of acidsfrom pollution and has also brought out the fact that increasedacidity is accompanied by the liberation of COg. He believesthat acidity and alkalinity are extremely powerful factors infish migration.

Mayor (1919) has shown that it is possible to detect oceancurrents by a study of the hydrogen-ion concentration.

Krogh and Leitch (1919) have studied the oxygen-unloadingtension of the haemoglobin of the blood in the plaice, cod, eel,carp, pike, and trout. They found that in the carp, eel, andpike, which are subjected occasionally to low oxygen tension(Powers suggests also CO, content), the oxygen content forunloading at 15° C. was low, 2 to 3 mm., while the oxygenunloading tension of the cod was 18 mm. and that of the plaiceand trout was about 10 mm. Low temperature decreasesthe efficiency of haemoglobin for carrying oxygen. A smallamount of carbon dioxide present serves greatly to diminishthe affinity of the haemoglobin for oxygen, so that in the carp,eel, and pike with a COj tension of 1 per cent, the unloadingis increased to 7.5 mm.

Roule (1914 et seq.) has long contended that salmondirected by an actual need, migrate towards a richer supply ofoxygen.

Powers (1921) cites the experimental work of numerousauthors to prove that before fresh water or marine fishesexhibit oxygen want, the oxygen content of fresh water andof sea water as well must be reduced to about 1.7 to 0.4 c.c. of

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Examination of Influences on Fish Migrationoxygen per litre. He also shows that the oxygen content ofthe waters where Roule's salmon were found was in excess ofthe amount necessary for the apparent well-being of the fish.

Working with herring and salmon smolt near the PugetSound Biological Station, Powers found (1920, 1921) that thegreatest number of herring apparently preferred water witha PH varying from 7.76 to 7.73, while the salmon smolt werepresent in water ranging from PB 7.98 to 8.08. His fieldstudies were preceded by careful laboratory experiments withrelatively small numbers of fish of several species.

In correlating the work of Krogh and Leitch and otherswith his own observations on the marine fishes, Powers asks(1921) what part the CO, tension plays in nature as affectingthe unloading tension of the haemoglobin in the blood of fishes.He states: "The very fact that they found that the fisheswhich are subjected occasionally to lower oxygen tension andhigher carbon dioxide content have a lower unloading oxygentension than those not subjected to these conditions ; and thefact that the experiments and field observations recorded(Powers, 1921) show that the fishes which live on the bottomand among the vegetation did not react to a gradient ofhydrogen-ion concentration, while the more freely swimmingforms did so and were found also in water having a PH ator near that to which they reacted positively in the experiments,are very suggestive."

Powers concludes that the hydrogen-ion concentration, orthe carbon dioxide tension of the water, has a considerableinfluence on the movements of pelagic fishes.

Miss Jewell has emphasised (1922) the significant fact thatfish are exceedingly sensitive to changes from the hydrogen-ion concentration to which they were accustomed.

Coker (1923, 19230) has made important studies of therelation between acidity and the occurrence of brook trout andother fishes in freshwater streams. He urges the importanceof further studies on this important environmental actor. Thetrout is less adapted than other fishes to live under conditionsof low oxygen pressure. Coker has been much struck withthe apparent preference of brook trout for acid streams, andwith the correlation between the observations of Gardner and

VOL. II.—NO. I. 97 G

F. E. ChidesterLeetham (1914) that trout in saturated water consume lessoxygen at the lower temperatures.

It is of interest in this connection to examine the tables ofFox showing the c.c. of oxygen in a litre of water at differenttemperatures and salinities, when the water is saturated withthis gas (Murray and Hjort, 1912, p. 254).

Salinity.

Temp.

o°C10" C.20° C.30° c.

Zero per thousand.O, in tc . per L

10-298-oa6-57S-57

20 per thousand.O s in cc. per 1.

9-017-io5-88490

35 J>er thousand.Oj in tc . per L

8-036-405-354-5°

" At 300 C, a litre, of water saturated with oxygen containslittle more than half as much oxygen as at o° C. Normallythere is more oxygen in the cold water-masses of the Arcticand Antarctic regions than in the warm water-masses of thetropics. Salinity is not such an important factor in thesolubility of oxygen as temperature" (Murray and Hjort,1912).

Significant work has been done by Lillie and Shephard(1923) on the relation between the PH and reactions of theworm Arenicola to light. In this particular animal, positiveheliotropism requires almost neutral or slightly alkalinereaction.

As we proceed further with studies of alkalinity and aciditywe find that they bear important relations lo the distributionof plants and animals (M'Gregor, 1921 ; Arrhenius, 1921 ;Atkins, 1921, 1923; Coker, 1923; Powers, 1921 et seq. ;Shelford, 1923).

Like other factors discussed in this paper, hydrogen-ionconcentrations must be reckoned with in field studies of thefuture on fish migration. The wrjter inclines to the belief ofShelford, Powers, and Coker in the great significance of thisaddition to the apparatus of the true field ecologist.

Pollutions.—Much work has been done on the subject ofstream pollution, and the situation is becoming increasingly

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Examination of Influences on Fish Migrationgrave as great industrial plants persist in discharging theirwastes into creeks and rivers. There is no question that fishare repelled by poisons in the water. Some species are soextremely sensitive that they will not pass through a pollutedarea, while others will continue on to their native spawninggrounds.

Waste substances may be classified as toxic-repellent,toxic - attractive, and non - toxic oxygen - absorbing. Thetoxic-repellent wastes have a direct effect in driving fish fromstreams; the toxic-attractive wastes such as gas wastes maylure the fish to their death (Shelford, 1917, 1918).

Non-toxic oxygen-absorbing wastes, such as the wastesfrom milk plants and fish canneries or from city sewage, mayputrefy and absorb the oxygen in a limited area. These lastare believed ultimately to furnish fish food by increasing theorganic matter that will support the small organisms uponwhich many fish feed.

Useful summaries of the literature have been prepared bythe U.S. Bureau of Fisheries (Stream pollution, 1919), and bySuter and Moore (Stream pollution studies, N.Y. StateConservation Commission, 1922), while significant investiga-tions by Prince (1899), Knight (1901), and others indicate thebelated interest that is being taken in the preservation of thenatural resources of our waters.

Suter and Moore {loc. cit.) have prepared a table thatshows how much dilution of wastes is necessary before fishlife may be preserved in a stream.

Tolerance of fishes to trade wastes (Suter and Moore,1 9 2 2 ) : —

No dilution required—sawdust and treated sewage.Dilution less than 1 : 10—raw sewage, fibre factory wastes.Dilution from 1 : 10 to 1 : 100—spent dyes, paper mill wastes.Dilution 1 : 100 to 1 : 1000 — gas manufacture wastes, wastes from

bleacheries.Dilution 1 :1000 to 1: 10,000—caustic lime, bichloride of mercury, etc.Dilution 1 : 10,000 to 1 : 100,000—lime, strong acids, gas tar.Dilutions greater than 1 : 1,000,000—copper sulphate, bleaching powder.

The disappearance of many of our food fishes from thecoastal streams is undoubtedly due directly to the influence ofwastes, and in most cases it would be possible at small expense

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F. E. Chidesterto arrange for the discharge of such waste into tanks or poolswhere much of value might be reclaimed. The chief difficultyseems to be in arousing the interest of the owners of thefactories concerned, as many of them are content to do thingsin the old way, regardless of the interest of the public or eventhemselves.

4. Internal Influences.Senses.—There is great variation in fishes as regards their

use of the senses. Some are predominantly olfactory orgustatory, while others are dependent upon vision for directingtheir movements. In all, the temperature sense is of paramountimportance.

Olfaction, Gustation. (Chemical sense). — Parker * hasrecently summarised the work of many authors on the questionof the chemical sense in fishes. In the migratory teleostswith which we are concerned, the olfactory pits are dorsaland not connected with respiration, but are purely sensoryin function.

Parker (1910, 1911, 1913), Sheldon, and others have demon-strated that fish have such a well-developed olfactory sensethat they can detect odorous substances in the.water at quiteconsiderable distances. Parker concludes that fishes have achemical sense dependent upon free nerve endings; smell,dependent upon the olfactory nerve which is a rather highlydeveloped distance receptor; and taste which is dependentupon the taste buds.

Shelford and Powers (1915) have successfully shown thatthe herring and other fishes are sensitive to variations in thesalinity of the water. The determination of acidity or ofalkalinity (Powers, 1920, 1921 ; Jewell, 1922; Shelford, 1915,1923 ; Coker, 1923) unquestionably is dependent upon thechemical sense and probably in part upon the allied sensesof smell and taste.

Shelford states (1915): " I t is not necessary to appeal toinstinct to explain the return of certain salmon to certainrivers or the running of herring in certain localities, since theirorigin in the region and limited tendency to leave it (Johnstone,

* G. H. Parker, 1922, Smell, Taste, and Allied Senses, J. B. LippincottCompany, Philadelphia, Pennsylvania.

IOD

Examination of Influences on Fish Migration1908), coupled with their ability to detect and follow slightdifferences in water, is a sufficient explanation of all theirpeculiar migrations."

Obviously the important work of Parker, Shelford, Powers,and others on the delicate sensibilities of fishes to changesin the salinity and PH of the water, has a most direct bearingon the migrations of fishes and an interesting relation tothe problem of pollutions.

Parker has suggested to the writer that it is barely possiblethat a certain race of fish may give off emanations that differchemically from those of other races, and that one mightattribute the return of individual races to home streams totheir power to sense the familiar emanation. While this wouldseem to be a difficult thing to prove, it is worthy of considera-tion in view of man's unwillingness to permit things to gounexplained!

Vision.—As has previously been pointed out in this paper,the work of Lyon (1904, 1909) indicates clearly that fish willreact sharply to currents even if the currents are not directlyin contact with them, providing they are able to see thebank alongside.

We are not concerned with colour vision of fishes, andit is of only passing interest to note that Sumner (1911)and Mast (1916) have discovered that flatfish are unable tosimulate their background in pattern or shade unless theeyes are functioning.

Hess believes that fish are colour-blind (1908, 1912).White believes that there is evidence for a certain degreeof discrimination (1919). Reeves (1919) holds that in thesunfish and the horned dace at least there is discriminationof light of longer wave-length from light of shorter wave-lengthand from white light. She associated a feeding response withthe stimulus of restricted wave-length. (See Reeves, 1919,for an excellent bibliography, and Washburn, The AnimalMind, Macmillan, 1917, for a discussion of sensory reactionsof vertebrates.)

In the section under "lights and shadows" in this paperwe have indicated already that while fish vary considerablyin their light sensitivity, there is no question that their ability

VOL. II.—NO. I. IO I G2

F. E. Chidesterto migrate long distances is in part due to the visual sense.That light may even influence the reactions of a fish totemperature has been shown by the writer (1923) in theteleost Fundulus heteroclitus. Other work by Cole (1922)on a salamander, and by Jordan, H. E. (1917), and Crozier(1918), on fishes, indicates the importance of both vision andcutaneous photosensitivity in the behaviour of fishes.

Tactile and Kinaesthetic Senses.—In connection with theorientation of fishes to currents, we find that the work ofLyon, Parker, Chidester, and others indicates clearly thatthe senses involved include touch and the kinaesthetic sense.

Parker has shown (1902) that in the teleosts, surface wavesand current action stimulate fishes in which the lateral linenerves have been cut, and he assumes, therefore, that thegeneral cutaneous nerves for touch are the ones involved.

Lyon, in a paper on compensatory motion in fishes (1900),demonstrated that if the tail of a dogfish is turned to a givenside the dorsal and anal fins will bend towards that side,as when the skin is stimulated. Parker comments (1909) onthe fact that a 2 per cent, solution of cocaine applied to theskin of the tail will cause this latter reaction to disappear.

Parker (1909) found that in the dogfish tactile stimulationproduces movements of the nictitating membrane and thefins. He divided the surface of the body of the dogfish intofive tactile regions characterised by the response resulting fromtheir stimulation. Mechanical stimuli induce fin motion andare unquestionably the cause of rapid changes in the directionof swimming.

The writer (Chidester, 1921, 1922) was much impressed bythe fact that contact with a swift stream would attract the fishin experimental troughs away from more favourable and other-wise more attractive liquids flowing at that time with lessforce. Poisonous and normally repellent solutions could bemade temporarily more attractive by increasing the force ofthe current.

Lateral Line.—While much has been done by otherworkers, including Schulze (1870), Bonnier (1896), and Lee(1898), G. H. Parker has contributed the most satisfactoryinvestigation on the function of the lateral line in fishes.

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Examination of Influences on Fish MigrationHe has shown (Parker, 1902, 1905) that the lateral line

organs of several species of teleosts are not stimulated bylight, heat, salinity, food, oxygen, carbon dioxide, foulnessof water, pressure of water, currents, or sounds. Theyare stimulated by vibrations of low frequency, about six persecond; and experiments as well as histological investigationsindicate that the lateral line organs are intermediate in functionbetween the organs of touch and the ear, which is, of course,sensitive to vibrations of high frequency.

Parker would hold that while the lateral line organs are notsensitive to currents, and therefore not particularly importantto the migrating fish in its orientation against moving water,they are stimulated by surface wave-movements produced byair on the water or by objects falling into the water, andthus may be important in warning the fish of otherwisedisturbing influences.

On the other hand, Hofer (1908) holds that in Parker'soperations on fishes, when he cut the lateral line nerves healso destroyed the nerves supplying the skin of the head.Hofer believes that the skin nerves are the ones affectedby slow vibrations in the water, and that the true functionof the lateral line organs is response to streaming movementsin the water.

Whether we accept the theory that the skin nerves arethe ones that determine orientation to currents, or that thelateral line nerves are the ones involved is, of course, debatable ;but the writer holds to the assumption of Parker that thegeneral cutaneous nerves are the ones chiefly involved inrheotropic response, while the lateral line nerves serve in anauxiliary capacity.

Hearing.—Parker (1902, 1908, 1911, 1912) has summarisedthe work of Kreidl, Lee, and many others on the ear in fishes,and references to their work may be found in his accompanyingbibliographies. Parker has concluded that in the Squeteague(Cynoscion regalis) the utriculus has to do with equilibriumand muscular tonus, while the saccular organ is the chief organof hearing (1908). Parker finds that while most sounds arerepellent to fish, some may be lures to particular species (1911).The surface between the water and the air is a screen through

103

F. E. Chidesterwhich little sound passes, but sounds that actually reach thewater are according to Parker quite effective stimuli.

Bernoulli, working with eels and trout, found (1910) thatpistol shots as well as the muffled sound of a bell were notstimuli to the fish.

He concluded that the reactions of fishes to stimuli aretactual and visual responses to the mechanical motion of thewater, and not true auditory responses.

It is quite probable that the roar and vibration due towaterfalls are attractive to many fishes, rather than repellent,and whether the fish actually hear the sounds as man does,or only sense the vibrations through the pressure of the waves,is of little moment in this problem. The writer, however,believes that Parker has proven his point for the minnow,Ftmdulus heteroclilus, and the Squeteague, Cynoscion regalis.

Temperature.—One of the greatest factors in the behaviourof fishes is their response to temperature change.

We find that, by means of heat and cold corpuscles inthe skin, fish proceed towards warmer or cooler water, and thatit is the relative temperature rather than the absolute tempera-ture that determines their activity. The work of numerousinvestigators has been summarised elsewhere in this paper,and so we may content ourselves at this time with pointing outthe following.

Herring are sensitive to very slight temperature changes,according to Shelford and Powers (1915), reacting to differencesas small as 0.20 C.

It has been shown that temperature changes influence thereactions of fishes to light, salinity, PB and to internal factorssuch as the developing gonads.

Unquestionably this sense is the greatest single factor thatwe find influencing the metabolism and behaviour of fishes. Itmust even be considered in connection with the instincts of thespecies.

Physical Condition of the Body—Size.—There is apparentlyno relation between the length of the fish and its ability tomigrate. It.is quite certain that fishes travel upstream andleap waterfalls, even when they are at almost the maximumgrowth for the species.

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Examination of Influences on Fish MigrationAs regards the weight, we find that migratory fishes vary

from a few ounces in weight to as much as 85 lb., the weightof the Chinook salmon.

Fat.—It has been conclusively shown by Greene (1913aand 1913^) that fat is the immediate source of the energyexpended by the salmon during the spawning migration. Thefollowing discussion is quoted from Greene's papers. Salmonfat is stored in the body during the stage of feeding andreaches a maximum at the time the feeding stage ends atthe beginning of the migration fast. Storage (according toGreene) is in muscles and the intermuscular connective tissues.Storage tissues of minor importance are cutaneous and otheradipose tissues such as the liver, the alimentary tract, and theskeleton.

The superficial dark muscle is loaded with fat at all stagesof the life cycle, especially as the spawning migration begins.The deep lateral pink muscle is loaded with intermuscular fatat the time of maturity, but has little traces of fat during thefeeding stage.

The pancreas of the salmon is diffuse, scattered over thepylorie caeca, mesenteries of the stomach and intestine, theinner loop of the stomach, and the mesentery of the spleen.

The pancreas is abundantly active during the migrationfast, producing an internal secretion that is rich in Upases,chiefly discharged into the tissue-spaces, reaching the bloodstream.

The pancreatic lipase produced during the fasting periodis "chiefly discharged into the tissue-spaces, reaches theblood stream, and is transported by the circulation to thetissues of the body, including the fat-storing tissues and theactive fat-using muscles" (Greene, 1913a).

In one of Greene's investigations he has shown (1913^)that the primary function of the large number of pylorie caecaof the salmon stomach is fat-absorption, with the intestine alsoan important region of fat - absorption. The cardiac andpylorie types of epithelium of the stomach also absorb fat

These investigations offer convincing evidence of the powerof fat-storage that is so necessary to an animal migratingthousands of miles without feeding en route. That there is a

F. E. Chidesterrelation between the condition of the body with respect tostored fats, and the time when such an animal begins tomigrate into fresh water, goes without saying.

Specific Gravity.—In connection with a study of the air-bladder and the specific gravity of fishes, Taylor has pointedout (1922) that a fish which increases in fat-content diminishesin specific gravity. He states that "a t 29.34 P e r cent, fat,the fish without an air bladder would be in equilibrium withsea water, and at 46.55 per cent, fat (if it were possible) wouldfloat in fresh water without an air bladder."

Taylor believes that a fish living at sea and accumulatingfat will find itself more at home physically in fresh waterwithout enlarging the air-bladder, and asks the pertinentquestion, "May not this be the influence which directs salmonand shad from salt water to the mouths of rivers ? "

It is possible for fish to adjust their specific gravity byreducing the size of the air-bladder when they migrate fromfresh water to salt water, and by secreting oxygen into thebladder, and thus enlarging it, when they move from salt waterto fresh water. Taylor concludes that increased fat rendersnavigation in salt water more difficult and fresh water thebetter physical medium. This evidence links up well withthe observations of Greene, Paton, and Hjort on the bodycomposition of salmon and herring at different stages.

Gonads. — Gurley, in a paper on "Biological-EmpiricalPsychology" (1909), adds to his earlier notes on the migrationsof fishes the interesting statement that in the fishes wehave an "intoxication factor," since paralleling the seasonaldevelopment of the reproductive organs, in-shore movementbegins, inherited from the parents who responded to similarstimuli and were able to spawn successfully. Obviously theparents selected proper environments for such spawning, elsethere would have been no offspring to continue the habits.

Johnstone, in a small book Life in the Sea (1911), citesthe intoxication theory of Gurley, and states that the "elabora-tion of an internal secretion from the ovary or testis producesan intoxication and impels the fish to seek water of definitephysical conditions." The writer of this review believes thatthe influence of hormones from the gonads is responsible for

106

Examination of Influences on Fish Migrationincreased activity of the fishes in any case, and that theirsubsequent behaviour is in part dependent upon otherfactors. These factors, which have been discussed else-where in the present paper, have been the basis of muchconjecture for years.

Temperature.—It is not necessary to do more than mention,by way of reminder, what our literature survey has alreadyshown that every factor under discussion is regulated by thatrise in temperature which increases chemical action and alsoincreases, up to a limit of course, the speed of the responseof an animal to stimuli. With increased metabolic activityin the living organism a high temperature becomes intolerableafter a time, and the fish seeks cooler waters.

Chemical Conditions.—Without attempting to discuss thematter in detail again, we may point out a few facts relative toenvironment, and indicate the relation of the changing chemicalcondition of the animal to its environment.

Roule has upheld the thesis that salmon migrate towardsa richer supply of oxygen, because of an actual need for it.Powers and others have concluded that the carbon dioxidetension of the water determines to a large extent the move-ments of pelagic fishes.

We must agree that metabolic activity accompanying fat-accumulation and gonad-development will create new needsas regards the environment, and that while the ensuing restlessmovements of the fishes may not always direct them immedi-ately to the needed new locality, they do result in securingoptimum conditions for many who will perpetuate in theirdescendants the habit of return.

It is likewise evident that fishes inherit a certain degreeof permeability, with an optimum salt-content of the bloodand of the tissues, and that the ability of the present-dayfishes to adjust themselves to changed external conditionsis probably dependent upon a capacity that was establishedin their ancestors during a period following marked continentalupheaval, with the receding of saline waters.

We may conclude, therefore, that while the physical andchemical demands of the fully - fed or fattened fish withdeveloping gonads, direct it towards cooler and fresher water,

107

F. E. Chidesterit continues upstream because of the stimulus of running water(stream pressure), favourable in oxygen content.

Unfavourable chemical conditions will kill the eggs offish that are not vigorous enough to reach the spawninggrounds that have been established for that species. Whatevermay have been the salinity of the water when our present-dayanadromous fishes began spawning inshore, it is certain thatnow, in the case of many species, their maturing eggs demandboth plenty of oxygen and a salinity that is much less thanthat of sea water.

While this is not the place to discuss the migration ofthe eel, it must be evident from the work of Schmidt thatwe have to consider the internal condition of the body incatadromous forms as well.

5. General Conclusions.1. Gilbert and others have shown that three or more

years after they are spawned, mature male and female salmonwill separate into races belonging to the parent stream andreturn to ancestral spawning grounds.

2. While fish will migrate past obstacles and over bottomsof a distinctly unfavourable type, they will seek out spawninggrounds that are most favourable. Survival of the fitdetermines the habitual characteristics of the grounds forany given race.

3. Fish respond to relative motion, the moving opticalfield acting as the stimulus, but they also respond to theforce of moving water, reacting to tides and currents.

4. There is much variation in the reaction of fishes tolight, but they share with other animals a sensitivity to suchstimulus, and their behaviour in the presence of other stimuliis affected by lights and shadows.

5. Temperature is the most important factor in fish migra-tion, since it affects not only the chemical processes of theenvironment but also has a profound influence on the rate ofmetabolism of fish and their response to external stimuli.

6. Search for food is an important agent in the dispersalof fishes and leads many species to travel from the deeperwaters of the ocean to the shallows offshore, or even up

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Examination of Influences on Fish Migrationinto fresh water, before they are mature. It bears littlerelation to spawning migration, however.

7. While variation in salinity is important in determiningthe range of some species, we have records of thirty-threespecies (Mather) of fishes that readily acclimatise themselvesto fresh and salt water. Anadromous fishes adapt themselvesto changes in osmotic pressure by changing slightly theosmotic pressure of the blood.

8. There is some evidence for the belief that anadromousfishes, as well as those passing their whole life-history in eithersalt water or fresh water, are susceptible to slight changesin acidity or alkalinity. That hydrogen-ion concentrationbears an important relation to the range of dispersal ofpelagic fishes seems to be well established. Roule has longcontended that the salmon responds to a need for higheroxygen content. Powers and others emphasize the carbondioxide tension or PH, as the important factor, more so thansalinity.

9. Fish are driven from the mouths of rivers emptyinginto the ocean by the pollutions from factories, canneries,and mines. In some cases they may spawn in regions toopolluted to permit the eggs to live, and so a race of fishmay be destroyed for that particular stream.

10. By means of the olfactory, gustatory, and chemicalsenses, fish trace food and distinguish favourable fromunfavourable waters. That they are able to detect emana-tions from ancestors and thus return to their parent streamsis rather unlikely, although it is an interesting conjecture.

u . Vision is important in connection with the progressof fishes upstream and undoubtedly plays a great part intheir return to former haunts.

12. The tactile and kinsesthetic senses influence thecharacteristic reaction to fishes to currents which enablesthem to travel far up rivers and creeks.

13. The lateral line sense bears little relation to migrationin fishes, while the poorly developed sense of hearing is evenless important.

14. Temperature sense, located in the heat and coldcorpuscles of the skin, is extremely important in connection

109

F. E. Chidesterwith migratory movements, and is most striking in itsmanifestations, as only slight relative changes in the tempera-ture of the water are sufficient to bring about the movementsof vast shoals qf fishes.

15. Size and weight in themselves have no appreciablerelation to the migration of fishes, except as they influencethe specific gravity and rate of metabolism.

16. Fat not only furnishes energy for long migrations,but it is, according to Taylor, the cause of movements fromsalt to fresh water, since it reduces the specific gravity somuch as to force some species to seek a less buoyant medium.

17. Developing gonads exert an influence on the movementsof fishes, since hormonic stimulation increases bodily activityand creates a demand for some new, definitely favourableenvironment. The environment sought is one that ancestralsuccess has selected as the optimum,

18. The chemical condition of the body, with referenceto oxygen content, carbon dioxide tension, lactic acid accumu-lation, and salt content are all important factors in reactionsto stimuli and in creating a need for movement to a newenvironment.

19. In all probability, the initial movements of anadromousfishes are from deeper waters to the shallower regions inshore,and until maturity they are primarily directed by the searchfor food and by temperature differences. At maturity, thecourse into fresh water is determined by increased gonadialdevelopment and stored fat, which create an urgent needfor water with less buoyancy and more available oxygen.

20. Migration up a given stream is determined in partby its accessibility at the time of the greatest internal urge,and steady travel is due to the reaction of a fish to currentstimulus under favourable conditions of temperature and witha chemical content of the water that is at that time theoptimum. The distance travelled is regulated by the periodof development of the eggs after the animal has become fullyfed, and this physiological factor is of course determined byan inherited tendency.

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Examination of Influences on Fish Migration

6. References.Allen, E. J. (1909), '•'Mackerel and Sunshine," Journ. Marine BioL Assoc. of the

United Kingdom, N.S., 8, No. 4, 394-406.Amemiya, Ikusaku (1931), "Effect of Salinity on the Development of the Egg of

Land-locked Saltnonoid Fishes, Hypomesus and Salanx," Suisan Gaikai Ho^ 8,No. 3, 189-95.

Araki, Ushihei, and Handa, Yoshio (1921), "On the Amount of Oxygen consumedduring the Development of Salmon Eggs," Hokkaido Fish. Exp. Sta. Doc.,pp. 1-13.

Armistead, J. J. (1894), "Atmosphere and Other Influences on the Migration ofFishes," Bull. U.S. Bur. Fistu, 1893,18, 93-99.

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Reclamation of Alkaline Land," The Cairo Sc. Journ., 10, Nos. 104 and 105.Atkins, C. G. (1874), " Habits of Migratory Fish," Report U.S. Bur. Fitk^ pp. 591-94.Atkins, W. R. G. (1922), "Some Factors affecting the Hydrogen-ion Concentration

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F. E. ChidesterShelford, V. E. (1918a), "Ways and Means of measuring the Dangers of Pollution

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