Gastric evacuation rates and daily ration of piscivorous coho salmon, Oncorhynchus kisutch Walbaum

Effects of temperature and meal size on gastric evacuation rates of juvenile coho salmon, Oncorhynchus kisutch , consuming sockeye salmon, O. nerka , fry were examined and used in the estimation of daily meal, daily ration and number of fry consumed by coho in Chignik Lake, Alaska. Evacuation of fry by coho was best described by a negative exponential model (average R² = 0.93). A square root model also provided a good fit (average R² = 0·93), but the y-intercepts deviated more from the expected value than did the y-intercepts of the exponential model. The effect of temperature ( T , 5–13° C) and meal size (MS, 0·166–0·367 g) on the exponential evacuation rate (r_e, h^-1) could be described as
In the lake, coho fed continuously during the 24-h period in early June 1986 and 1987. Estimates of daily meal and ration of coho calculated by the Eggers method and the geometric mean of prey weight ranged from 0·224 to 0·435 g (2.1–4.4% body wt) depending on location and year. The Elliott & Persson method provided similar estimates of food consumption, whereas estimates based on the Pennington method and square root evacuation of prey differed from the exponential models. Sockeye fry represented 93% of the total prey weight. The average number of sockeye fry consumed per coho per 24 h, based on the arithmetic mean of prey weight, was 3·0–3·9 fry.     

Pheromones and the water source preferences of adult coho salmon Oncorhynchus kisutch Walbaum

It has been proposed that population-specific pheromones released by juvenile salmonids guide the adults on their homing migration (Nordeng, 1977). To evaluate this hypothesis, adult coho salmon, Oncorhynchus kisutch , were tested in a two-choice apparatus with a variety of water sources. Coho salmon preferred home water without coho odours over an unfamiliar water source (city water). Adults preferred water conditioned by juveniles of their own population over plain city water, but did not prefer water conditioned by juveniles of their own population over that of another.     

Strontium marking of hatchery reared coho salmon, Oncorhynchus kisutch Walbaum, identification of adults

Hatchery-raised coho salmon were marked with stable strontium prior to their release to sea. Returning marked spawners were correctly identified after 18 months at sea by measuring the Strontium (Sr) concentration of the central region of their scales and vertebrae.     

Risk-taking behavior in weight-compensating coho salmon, Oncorhynchus kisutch

The effects of food restriction on predation risk-taking behaviorwere studied in juvenile coho salmon, Oncorhyndtus kisutch,during the period before seawater migration in the spring. Aradiographic technique enabled the study of individual foodintake in a safe and risky food patch before and after exposureto a piscivorous predator. The study revealed a significantincrease in food intake and specific growth rate in the weeksfollowing deprivation, resulting in compensatory growth anda recovery of the weight loss caused by dietary restriction.The increase in food intake resulted from a change in risk-takingbehavior. Following a period of diet restriction, the fish habituatedfalter after predator exposure, and the proportion of fish inthe risky patch was significantly higher than before deprivation.Deprived fish took greater shares of the group meal comparedwith control fish, and the pattern of the individual share ofthe group meal after food restriction indicated a change inthe social hierarchy. This study indicates that risk-takingbehavior is state dependent and changes temporarily to compensatefor a period of food restriction. The results are discussedin terms of tradeoffs between food and risk in a period leadingup to an ontogenetic habitat shift.     

Smoltification in the net-pen culture of accelerated coho salmon, Oncorhynchus kisutch Walbaum: prediction of saltwater performance

Prediction of the success of coho salmon, Oncorhynchus kisutch , in making the transition from fresh water to salt water was investigated by the use of statistical comparisons between several freshwater variables and several measures of saltwater performance. Data were collected from two consecutive broodyears of coho salmon that were derived from a nested mating design, grown under enhanced rearing conditions, and raised in marine net-pens. Equations were developed that could successfully predict percentage smolts and saltwater growth from morphological measurements taken in fresh water. However, saltwater survival was not predictable from these measurements. Criteria for predictive equations and the value of these calculations, as well as directions for future research, are discussed.     

Growth hormone and seawater adaptation in coho salmon, Oncorhynchus kisutch

1. Effects of growth hormone (GH) were examined on short-term aspects of seawater adaptation in coho salmon smolts. 2. Injection of somatostatin (SRIF) immediately prior to seawater entry suppressed plasma GH levels, but did not have any significant effects at 6 or 12 hr on hematocrits, plasma glucose or plasma Na+ levels. 3. Plasma GH levels increased 250% within 36 hr after seawater exposure. 4. Plasma glucose levels, in contrast, were significantly lower in the seawater fish after 36 hr post-exposure. 5. Plasma Na+ levels increased to 190 mEq/1 by 24 hr but subsequently returned to freshwater levels while hematocrits showed no significant changes over the 72 hr of exposure. 6. The significance of these results is discussed in terms of successful seawater adaptation in coho salmon.     

Characterization of coho salmon (Oncorhynchus kisutch) insulin

Insulin has been isolated from islet tissue of coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC and the complete amino acid sequence has been determined. The sequence differs from bovine insulin at 14 sites but all interchanges are conservative from the viewpoint of preservation of conformation. A comparison of insulin sequences from other fish is presented. Salmon insulin cross-reacts very weakly with antiserum to bovine insulin and vice versa. A completely homologous radioimmunoassay has been developed and used to estimate the insulin in salmon islet tissue and in plasma. The hypoglycemic effect of salmon insulin in salmon was more pronounced and persisted longer than that caused by identical doses of bovine insulin.     

The blood vasculature of the gastrointestinal tract in chinook, Oncorhynchus tshawytscha (Walbaum), and coho, O. kisutch (Walbaum), salmon

The venous and arterial vasculature of the chinook and coho salmon gastrointestinal tract were examined using corrosion casts and India ink injection techniques. Observations derived from 28 individuals of various sizes and of both sexes were used to construct simplified venous and arterial plans. Examination of the blood vasculature revealed the presence of a variety of anastomoses hitherto undescribed in teleosts.     

Sub-surface drift feeding by coho salmon (Oncorhynchus kisutch, Walbaum): a model and test

The results of a test of a mechanistic encounter model that predicts the size-frequency composition of the diet of drift-feeding coho salmon ( Oncorhynchus kisulch , Walbaum) are described. When all taxa in the drift were included in the model the predicted and actual diets differed significantly, although the model explained most of the variance between the diet and the predictions of a null model. When non-consumed taxa, including the distasteful and aposematic taxon Hydracarina, were excluded from the drift composition there was no significant difference between predicted and actual diets. The model's goodness of fit increased when it was modified to predict the biomass size-frequency diet composition, explaining 99% of the weighted sum of squared deviations between the diet and a null model. A number of alternate models are tested and a potentially useful simplification of the model is identified.     

Strontium marking of hatchery-reared coho salmon (Oncorhynchm kisutch, Walbaum)

In the management of saimonid populations it is often necessary to distinguish hatchery-reared from wild stocks. This study examines the feasability of marking fish tissue by substituting a biologically rare element, strontium, for calcium.
Sixteen-month-old hatchery-reared coho salmon ( Oncorhynchus kisutch , Walbaum 1792) were fed a diet, to which 10000 ppm stable strontium was added, for 60 days. Prior to their seaward migration in June 1976, the treated coho contained 32 times as much strontium in their vertebrae as did the control coho.
Sixty-eight precocious males'jacks' returned to the hatchery in the fall of 1976 and 1200 adults in the fall of 1977. Strontium-treated 'jacks' contained 1·4 times as much strontium as did control 'jacks' however, treated and untreated fish could not be distinguished as adults. The reduction in the strontium concentration of the treated fish could be accounted for by growth.     

Morpho-ecological patterns and feeding of coho salmon Oncorhynchus kisutch fry in the period of downstream migration

The principal patterns of feeding of downstream-migrant and coastal young of the year of coho salmon are considered. The so-called potential downstream migrants and residents, which differ in size and feeding patterns, were distinguished among coastal fry. It is assumed that identification of particular coastal specimens to phenotypic groups of downstream migrants or nonmigrants of young of the year of coho salmon may be determined even in the daytime by such parameters as the body length, feeding intensity, and food spectrum.     

Clearance of plasma corticosteroids during smoltification of coho salmon, Oncorhynchus kisutch

The plasma clearance rate (PCR) of radioactivity after a single intracardial injection of 3H-cortisol was elevated during the spring in yearling coho salmon, Oncorhynchus kisutch. Graphical analysis suggested a seasonal correlation between PCR and gill Na/K-ATPase activity. An explanation for this correlation is suggested. The major metabolite of 3H-cortisol in plasma was 3H-cortisone. It appeared rapidly following injection of the original radiotracer.     

Changes in intestinal fluid transport associated with smoltification and seawater adaptation in coho salmon, Oncorhynchus kisutch (Walbaum)

The intestinal role in osmoregulatory preadaptation of freshwater-adapted (FW) yearling coho salmon during smoltification was examined. Measurements of intestinal net fluid absorption (J_V) using an in vitro sac preparation showed that J_V of FW parr was significantly less than that of either FW or seawater-adapted (SW) smolts. From two to four weeks following the springtime thyroxin surge, J_V increases in FW coho to a level comparable with that observed for SW smolts. J_V remained elevated in FW smolts throughout most of the summer and then decreased in the autumn. Two months after the thyroxin peak, intestinal wet weight per unit serosal surface area increases. Coho stunts resulting from premature transfer into sea water had significantly higher J_V than that seen in SW smolts. The elevated J_V of stunts is only partially explicable on the basis of differences in body weight between stunts and smolts.
Our observations indicate that an increase in intestinal fluid absorption is a preadaptive change associated with smoltification occurring in concert with alterations in renal and branchial osmoregulatory mechanisms. The timing of the increase in J_V suggests a phase relationship to the thyroxin surge. This temporal relationship may help to explain the efficacy of using changes in plasma thyroxin levels to predict hatchery-fish release dates that may optimize eventual seawater survival.     

Evidence for crypsis in coho salmon, Oncorhynchus kisutch (Walbaum), parr: substrate colour preference and achromatic reflectance

The crypsis hypothesis of salmonid parr coloration and behaviour is evaluated in light of the criteria for protective resemblance. A review of the literature indicates that salmonid parr coloration and behaviour correspond to a cryptic interpretation. Experiments on coho salmon, Oncorhynchus kisutch , parr substrate colour preference indicate that the behavioural correlate of appropriate background choice is satisfied. Absorption spectrophotometry of diapositives of fish and experimental substrates suggests that background matching is achieved through achromatic reflectance and absorption of wavelengths by the silvery sides and parr marks, respectively.     

Ontogeny of the olfacto-retinalis projection in coho salmon (Oncorhynchus kisutch)

Filling of nucleus olfacto-retinalis neurons by cobaltous lysine injections into one eye of coho salmon of different ages revealed that the terminal nerve projection to the retina is established when the fish leave their freshwater environment. At this time salmons go through a metamorphosis termed "smoltification." FMRF-amide-like immunoreactive neurons in the nucleus olfacto-retinalis already exist in pre-smolts before the retino-petal projection is established. Thus, for the first time in any vertebrate, a projection of the terminal nerve is shown to develop during an advanced ontogenetic state.     

Thyroid function, pituitary structure and serum lipids in Great Lakes coho salmon, Oncorhynchus kisutch Walbaum, 'jacks' compared with sexually immature spring salmon

Whereas spring salmon, Oncorhynchus kisutch , from Lake Ontario had no overt thyroid goiters, comparable Lake Erie spring salmon had a 44% goitre incidence. Goitre incidence in sexually precocious 'jacks' from Lakes Ontario and Michigan was 43–45% and 100% in 'jacks' from Lake Erie.
All fish displayed thyroid hyperplasia. The degree of hyperplasia (as indicated by thyroid follicle colloid content, thyroid follicle size and shape and thyroid follicle epithelial cell size) in Lake Ontario fish tended to be greater in the 'jacks' than in the spring fish; the reverse was true in Lake Erie fish. Serum total L-thyroxine (T4) concentrations in Lake Ontario spring fish were higher than in any other group. There were no differences in serum T, levels between the groups of 'jacks', nor were serum T, levels in 'jacks' and spring salmon from Lake Ontario significantly different. Serum total triiodo-thyronine (T) concentrations in Lake Ontario spring salmon were significantly higher than in all other groups and that in Lake Erie spring salmon greater than in all groups of 'jacks'. Serum T, levels in Lake Ontario 'jacks' were higher than in Lake Erie 'jacks'. Serum free fatty acid (FFA) and cholesterol levels showed significant interlake differences with lower levels present in Lake Erie salmon. Lake Erie 'jacks' appeared to have fewer and less well vacuolated pituitary gonadotropic basophils than 'jacks' from Lakes Michigan and Ontario. Putative thyrotrop cells appeared to be more numerous and more active in the Lake Erie spring salmon compared with Lake Ontario spring salmon. Prolactin, corticotrop and melanotrop cells appeared less active in spring salmon than in the 'jacks'.     

Induced thermotolerance and tissue Hsc70 in juvenile coho salmon, Oncorhynchus kisutch

We examined Hsc70 in gill, liver and caudal fin from coho salmon ( Oncorhynchus kisutch ) before (ambient, ~12 °C) and after a sublethal heat shock of 25 °C for 1 h. Increased levels were observed for at least 48 h in all three tissues. Attempts to demonstrate isoforms of this heat-shock protein were not successful using four different antibodies. However, one of these antibodies recognized isoforms in brine shrimp and oysters, two organisms in which the heat-shock response has been well characterized. Extracts of those organisms and coho salmon tissues were run on the same gels and evaluated on the same Western blots, at the same time. We believe that our results provide a reliable account of Hsc70 in these fish under these conditions. Limited experiments showed that induced thermotolerance was achieved in these coho salmon, lasting for about 1 week after the sublethal heat shock. These data suggest that increased levels of Hsc70 are correlated with induced thermotolerance in these fish.     

A genetic linkage map for coho salmon (Oncorhynchus kisutch)

Construction of genetic linkage maps is an important first step for a variety of genomic applications, such as selective breeding in aquaculture, comparative studies of chromosomal evolution and identification of loci that have played key roles in the evolution of a species. Here we present a sex-specific linkage map for coho salmon. The map was constructed using 148 AFLP markers, 133 microsatellite loci and the phenotypic locus SEX . Twenty-four linkage groups spanning 287.4 cM were mapped in males, and 33 linkage groups spanning 429.7 cM were mapped in females. Several male linkage groups corresponded to two female linkage groups. The combination of linkage groups across both sexes appeared to characterize regions of 26 chromosomes. Two homeologous chromosomes were identified based on information from duplicated loci. Homologies between the coho and rainbow trout maps were examined. Eighty-six loci were found to form common linkage relationships between the two maps; these relationships provided evidence for whole-arm fissions, fusions and conservation of chromosomal regions in the evolution of these two species.     

Epizootiology and histopathology of Parvicapsula sp. in coho salmon Oncorhynchus kisutch

The epizootiology and histopathology of the myxosporean Parvicapsula sp. was studied during monthly health surveys of 4 groups of coho salmon Oncorhynchus kisutch at a commercial farm in Puget Sound, Washington, USA, from 1984 to 1986. No Parvicapsula sp. was detected in histological samples taken from juvenile fish in fresh water, but the parasite was detected in fish from all groups 2 to 8 mo after transfer to seawater net pens. Groups placed in seawater net pens in November and December had a higher prevalence of infection, and a longer period of continuous detected infection, than those introduced into net pens in May. For the groups transferred to seawater in November and December, the highest infection prevalence (45 to 90%) was detected during the following March and April. Among 13 tissues examined histologically, only the pseudobranch and kidney were positive for Parvicapsula sp., with 26 (62%) of 42 positive fish showing infections only in the pseudobranch, 5 (12%) showing infections only in the kidney, and 11 (26%) showing infections in both organs. Both the pseudobranch and kidney were apparent primary infection sites, but pseudobranch infections appeared to persist longer in a population. Pseudobranch infections were frequently heavy and associated with extensive inflammation and necrosis of filament and lamellar tissues. The kidney had been the only infection site reported for Parvicapsula sp. in previous studies of coho salmon.