The preferred salinities of five Pacific salmon species were studied. Each species was shown to undergo a temporal sequence of preference changes. The sequence began with a preference for fresh water then changed in the direction of increasing seawater concentration, the terminal pattern indicating a preference for water of open ocean concentration. This preference sequence was shown to parallel closely the horizontal salinity gradients typical of estuaries through which juvenile salmon pass on their seaward migration. On the basis of this evidence the following orientation mechanism was postulated: that juvenile salmon are able to use estuarine salinity gradients as one of the directive cues in their seaward migration. Further study of this orientation mechanism showed that the initial part of the preference sequence develops unaffected by seawater exposure. By contrast the latter part of the sequence (corresponding to seaward end of the estuary) was found to depend on a period of exposure to seawater otherwise a regression to a premigratory freshwater preference took place. The sensory stimuli leading to the salinity preference response were shown to depend on a complex interaction of naturally occuring sea salts. Experimentally the simplest salt mixture which would elicit a normal response consisted of two cations (Na⁺ and Ca⁺⁺) and one anion (Cl¯). It was shown further that taste or the common chemical sense was the primary sensory modality underlying the response and that juvenile salmon have an ability approaching absolute salinity discrimination. Speculation concerning the evolution of the salinity preference orientation mechanism was presented. Published evidence favours the view that migratory salmonids evolved from nonmigratory forms with limited osmoregulatory abilities. On this basis it was proposed that originally the ability to orient with respect to seawater concentration was of direct survival value to the stenohaline ancestral salmonid. Later, as diadromous movements expanded along with euryhalinity, salinity preference became integrated into a temporal sequence of changes and thereby an orientation device useful for migration. / Science, Faculty of / Zoology, Department of / Graduate

Vertical distribution and onshore movement of maturing kokanee were studied by means of extensive gill net sets in Nicola Lake between 1958 and 1961. In late spring of 1959 maturing kokanee were found largely in the upper 30 feet of the lake but gradually dispersed to occupy all depths to 100 feet by mid-summer. A diel vertical migration occurred in which maturing kokanee moved surfaceward during the day and downward at night in 1959. In 1961 the reverse condition was observed wherein kokanee avoided areas of bright illumination during the day but moved surfaceward at night. No effect on vertical distribution of kokanee by extensive and rapid fluctuations of the thermocline, initiated by wind induced seiches, was noted in 1959 or 1961. The 1961 vertical distribution appeared closely associated to light intensity. Seasonal and diel changes in diet were observed in 1959. Chironomid pupae were the dominant food organisms eaten in late spring and summer. Planktonic crustaceans were consumed in greatest numbers in late summer, autumn and spring. Kokanee captured in mid-summer in the surface water (0-25 feet) generally had been feeding on planktonic crustaceans whereas those taken from below 25 feet contained largely chironomid pupae and larvae. Onshore movement of mature kokanee toward a spawning stream was initiated by falling light intensity and intensified by strong onshore winds. Possible mechanisms of location of the spawning stream were investigated. Migration to an inlet spawning stream and movement within the stream were recorded at two traps, one situated at the stream mouth, the other 1000 feet upstream. Movement into the spawning stream occurred only at night and was unaffected by changes in stream temperature and flow. A significant correlation was found between daily number of kokanee entering the stream and strength of onshore winds. Differences in sex ratio of the spawning runs and length of mature kokanee were recorded and possible causal agents discussed. / Science, Faculty of / Zoology, Department of / Graduate

The life cycle of Phflonema oncorhynchi was studied in sockeye salmon, Oncorhynchus nerka, from Cultus Lake, British Columbia. Gravid female worms from the coelom of sockeye spawners burst in lake water releasing living first-stage larvae. These were ingested by Cyclops bicuspidatus and developed to the infective third stage in the haemocoele. Development required 17 days at 12 C or 70 days at 8 C. Each of six hatchery-reared sockeye fingerlings were fed 14-70 copepods infected with third-stage larvae. Fourth-stage larvae were recovered from the peritoneal tissues of four fingerlings when examined four to ten days after infection. The later stages of development were studied by maintaining naturally infected sockeye salmon for two years in freshwater. These had early fourth-stage larvae in the parietal peritoneum and tunica adventitia of the swim bladder when captured as downstream migrants at Cultus Lake. When the fish were 26 months old, late fourth-stage larvae were found in the peritoneal tissues. These moved into the coelom when the fish were 32 months old and moulted to the preadult stage. The comparative morphology of mature worms collected from B.C. salmonids was studied. The type species, Philonema oncorhynchi Kuitunen-Ekbaum, 1933 was obtained from the type host, Oncorhynchus nerka, in the type locality, Vancouver, B.C. Philonema were also obtained from salmonids with a freshwater life cycle in a landlocked area, Kootenay Lake, which was once contiguous with the type locality of Philonema agubernaculum Simon and Simon, 1936. The morphology was constant for worms found in different hosts and geographical areas. Size was an unreliable characteristic and appeared to be a host-dependent variation. The type specimens of Philonema agubernaculum Simon and Simon, 1936 were examined and no differences in morphology found. / Science, Faculty of / Zoology, Department of / Graduate

The seasonal salinity preference of four species of Pacific salmon was examined. Each species showed a strong preference for hypertonic seawater during the normal period of migration. Pink fry (Oncorhynchus gorbuscha) and coho yearlings (O. kisutch) lost this preference during the summer in contrast to Chum fry (O. keta) and sockeye yearlings (O. nerka). Three other types of behaviour showed seasonal changes consistent with a transitory "migration disposition". A preference for hypertonic seawater was associated with high levels of activity, strong schooling tendencies and depressed aggressive behaviour. Subsequent seasonal changes showed a marked increase in aggressive behaviour accompanied by decreased levels of activity and group behaviour. A long daily photoperiod (16 hours) prolonged the behaviour complex associated with seaward migration. A short daily photoperiod (8 hours) delayed but did not totally inhibit the development of a hypertonic salinity preference and associated behaviour. The preference of chum salmon fry for a series of seawater concentration indicated an all-or-none type response. A consistently strong preference was shown for seawater hypertonic to plasma chloride levels as reported in the literature. No preference was shown for hypotonic seawater. A series of experiments in which the composition of an artificial seawater was altered indicated that under natural conditions the expression of a preference for salt water probably depends on the concentration of sodium chloride. The swiftness of the response (chum and sockeye) indicated stimulation of a peripheral salinity receptor. Coho underyearlings injected with mammalian somatatropin showed an increased although not statistically significant preference for hypertonic sea water. Both activity and aggressive behaviour were depressed in comparison to control fish. / Science, Faculty of / Zoology, Department of / Graduate

The relationship between osmoregulatory stress and locomotor performance has been investigated in juvenile salmonids during their adjustment to sea water. Transfer from fresh water to sea water produced a statistically significant depression of the maximum swimming speed of chum salmon fry (Oncorhynchus keta). The effect of sea water was immediate and reached a maximum fourteen hours after transfer. From thirty-six to eighty hours (the duration of the experiment) relatively stable performance levels were recorded. Some recovery from the initial effects of sea water was apparent but the swimming speeds of "recovered" fish were significantly lower than those of fry in fresh water. Statistically significant correlations between swimming speed changes and changes in total body chloride and water concentrations have been demonstrated. Since chum fry were too small to allow separate sampling of plasma and tissue, the Steelhead trout (Salmo gairdneri gairdneri) was used to investigate the sequence of events in the osmoregulatory adjustment of salmonids to sea water. Transfer into sea water was accompanied by increases in plasma concentrations of chloride, sodium and potassium, but not of calcium. Cellular dehydration resulted from transfer of cellular fluids to the extracellular phase, and from loss of water to the environment. Cellular levels of calcium and sodium rose markedly. Smaller increases in cellular potassium and chloride were noted. Changes in cellular sodium and calcium were primarily due to ion uptake. Increases in cellular potassium were the result of cellular dehydration since tissue levels of this cation fell slightly in sea water. The data indicate that impairment of the efficiency of physiological processes sensitive to altered electrolyte concentrations, and the utilization of energy in the restoration of body fluid electrolyte concentrations to regulated levels may account, at least in part, for reduced locomotor ability in salmonid migrants during their adjustment to sea water. Body size was shown to influence the extent and duration of changes in plasma and tissue electrolyte concentrations and distributions. In chum fry the governing factor appeared to be size, larger animals adapting more rapidly, and undergoing less extensive changes than did smaller fish. In Steelhead trout efficiency of osmoregulation was highest at certain stages of growth, and suggested that adjustment to sea water was best achieved during a restricted phase of their life history. This stage appeared to be that of late parr-smolt transformation. The operation of plasma electrolyte homeostatic mechanisms was indicated in the Steelhead trout and the possible roles of the withdrawl of ions from the circulating fluids by complex formation and by active excretion have been considered. / Science, Faculty of / Zoology, Department of / Graduate

A dialyzing technique was developed to concentrate an estrogen hormone fraction suitable for separation by paper partition chromatography and spectrophotometry assay. Estrogens were not found in sexually differentiating salmon embryos. Small amounts of estriol, estradiol-17β and estrone added to the tissue could not be recovered. However, horse testes assayed by the same technique showed the presence of estradiol-17 β and estrone in concentrations of .097 and .143 mg./kg., respectively. The assay of horse testes was carried out on.90 gram lots, whereas the one previous chemical assay was done on 28,000 grams. It is concluded that this technique is very satisfactory for extraction of estrogens from animal gonads, but that hormone added to whole salmon embryos is inactivated by-some unknown system. A partition technique recently developed by F. Mitchell and R. Davies for the extraction of estrogens from human placentae was slightly modified for use with salmon embryos. This method confirmed the negative findings obtained by the dialyzing technique. On the basis of these experiments, there is no evidence to support the hormonal theory of sex differentiation in fishes. / Science, Faculty of / Zoology, Department of / Graduate

Life history events of chinook salmon preclude determination of a critical size for this species by established methods. The use of size, rather than age, as a basic correlate of growth rate is discussed and compared to analagous treatment of physiological rates described in literature. Ecological opportunity and physiological opportunity are visualized as the two interacting components that determine growth, both of which are related to size attained. Growth opportunity occurs in stanzas which are entered at "threshold" sizes. The function, dw/dt = kw(x) is developed into a growth equation for linear dimentions, 1(z/t+1) = ɑ + (1z/t) and three methods of fitting this equation to growth data are demonstrated. Application is explored and discussed using steel-head trout and chinook salmon as examples. Significant differences in growth rate were found between life history types and sexes. The chinook data were then treated on a 1(t+1), 1(t) plot and it was shown how an apparent fit of the von Bertalanffy type growth equation can result from selectively fishing for the larger fish of any brood year. Accordingly, life history subgroups of a year class must either be treated separately or weighted according to relative abundance in determining critical size. The former alternative is followed in lieu of necessary weighting data. Natural mortality of a chinook population is estimated from the pattern of tag recoveries, taking advantage of the fact that maturity occurs at different ages for individuals of a year class and that the fishery operated mainly on maturing individuals. Annual instantaneous natural mortality was estimated to lie in the range 0.3 to 0.4. The growth equation was then transformed to a length-specific average annual instantaneous growth (weight) rate and critical size was observed to occur at maturity for each life history type. Since fishing is presently allowed on the immature stock, a size limit protecting the older life history types causes a loss in yield from the younger life history types. This loss might be offset, depending on the relative abundance of life history types in the stock, providing mortality due to hooking and releasing is negligible. Capture by trolling was found to subject feeding coho and chinook salmon to hyperactivity which may lead to a distressed condition or death, and death cannot be predicted from examination of individual fish at time of capture. Mortality of coho was estimated to be in the 0.95 confidence interval of 34 percent and 52 percent; of chinook in the 0.95 confidence interval of 40 percent and 71 percent. Time of maximum death rate is shown to coincide with the period of maximum blood lactate response. Survival occurred either when blood lactate did not reach critical levels (above 125 mg%) or reached critical levels and subsequently subsided. Holding salmon in a live box for 8-14 hours before release did not improve tag recovery, suggesting additional indiscriminant stress was caused at release. Adult coho in freshwater did not appear capable of lethal hyperactivity. This led to the hypothesis that cessation of feeding during spawning migration has adaptive significance for survival of Pacific salmon. The combination of natural mortality, mortality from hooking injury and delayed mortality from fatigue gave a total instantaneous first year mortality rate (exclusive of fishing) greater than 1.0 and possibly as high as 2.5. This mortality rate results in a critical size of not more than 22.5 inches and most likely about 15.0 inches fork length. It is thus concluded that for maximum yield in pounds (1) fishing for chinook should be restricted to their ultimate year (maturity) and (2) the use of non-selective gear should be encouraged. These recommendations are opposite to present practices. If fishing is to be allowed on the immature stock, size limits should be abolished. / Science, Faculty of / Zoology, Department of / Graduate

Coho underyearlings settle toward the bottom when illumination decreases. The critical intensity for this response was found to be approximately 1 foot candle. A study of the nipping phenomenon in coho and kamloops trout revealed that coho nip more Intensively than trout in a homotypic group. However; in a heterotypic group of equal numbers, trout nip more readily. In a heterotypic group coho nip less frequently and show a preference to nip other coho. By comparison, the nipping Intensity of trout is not reduced and they nip either species equally. Factors affecting nipping are size, color and light intensity. In a group of coho or trout, there is a marked tendency for the larger members to nip the smaller. Red and orange colors are least effective in eliciting a nipping response. Light intensity changes between 4- and 12 foot candles have no significant effect; however, below k foot candles nipping declines rapidly as illumination is decreased. The social releaser for nipping is movement but size and color are important components of the releaser. Additional patterns of behavior have been described for trout, namely, "threatening" and fighting. / Science, Faculty of / Zoology, Department of / Graduate

Both field and laboratory experiments have shown lethal effects from the deposition of silt on incubating salmon eggs. Because silting appears to deprive the eggs of sufficient oxygen, theoretical limits of flow and oxygen content of sub-surface water were studied. Data have been gathered on temperature, oxygen content, and rate of flow of water twelve inches below the surface of the gravel at Nile creek. Field determinations of oxygen consumption of pink, chum and coho eggs have been made. In heavily-silted portions of the bed there was an insufficient supply of oxygen for pre-eyed chum salmon eggs. A field method for determining oxygen content and apparent velocity of gravel water is presented. / Science, Faculty of / Zoology, Department of / Graduate

A method is described for measuring the preferential responses of fish to alterations in the chemical and physical nature of their environment. Changes in the responses of young chum salmon at various stages of growth to alterations in the environmental sea water content have been studied. The effects of small alterations in temperature (2 to 3 C° ) and in rates of flow of environmental liquids on the fishes' responses to salinity change, were also studied. Preliminary experiments on the responses of coho salmon fry to sea water are described. The results indicate that changes in the environmental sea water content, such as those encountered in the estuaries of salmon streams may exert a directive influence on the seaward movement of chum salmon fry. / Science, Faculty of / Zoology, Department of / Graduate