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.     

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.     

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.     

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.     

Characterization of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch)

Wild stocks of Pacific salmon in the Northwestern United States have declined in recent years, and the major factors contributing to these losses include water pollution and loss of habitat. In salmon, sublethal chemical exposures may impact critical behaviors (such as homing, feeding, predator-avoidance) that are important for species survival. Therefore, understanding the potential for these species to biotransform organic compounds within sensitive target tissues such as liver, gills and olfactory region can help estimate or predict their susceptibility to pollutants. In this study, we used real-time quantitative polymerase chain reaction (Q-PCR), Western blotting, and catalytic assays to characterize the expression of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch), a sensitive species in the Pacific Northwest. Gene expression analysis using Q-PCR assays developed for coho genes revealed the presence of the predominant cytochrome P450 mRNAs (CYP1A, CYP2K1, CYP2M1, CYP3A27) in the olfactory rosettes and provided quantitative mRNA expression levels in coho liver and gills. Q-PCR analysis revealed relatively high expression of the major CYP isoforms in the liver and olfactory rosettes, which was generally confirmed by Western blotting. Extrahepatic CYP expression was generally higher in the olfactory rosettes as compared to the gills. Catalytic studies demonstrated functional CYP1A-dependent ethoxyresorufin-O-deethylase, CYP2-dependent pentoxyresorufin-O-dealkylase, CYP2K1-dependent testosterone 16beta-hydroxylase, and CYP3A27-dependent testosterone 6beta-hydroxylase activities in liver, but not at detectable levels in gills. In contrast, flavin-containing monooxygenase (FMO)-dependent thiourea S-oxidase activity was readily observed in the gills and was substantially higher than that observed in liver. Collectively, the results of this study suggest that the olfactory rosettes are important sites of extrahepatic biotransformation in coho salmon, and that tissue specific-differences in Phase I metabolism may lead to contrasting tissue-specific biotransformation capabilities in this species.     

Top-down and bottom-up control of life-history strategies in coho salmon (Oncorhynchus kisutch)

Sexual maturation profoundly affects population dynamics, but the degrees to which genetic, top-down, and bottom-up controls affect age at maturity are unclear. Salmonid fishes have plastic age at maturity, and we consider genetic and environmental effects on this trait by developing fitness functions for coho salmon (Oncorhynchus kisutch). The functions are based on size-specific survival and reproductive success, where reproductive success is the product of fecundity and ability to defend nests (females) or the product of sperm volume and ability to mate (males). We model genetic and bottom-up controls (e.g., food availability) with an environmentally explicit growth function and top-down control (predation mortality) with survival functions that consider both size-dependent and size-independent mortality. For females, we predict that early maturation rarely maximizes fitness, but males can maximize fitness by maturing early if they grow well in freshwater. We predict that early maturation is most affected by the bottom-up effects of resource distribution at sea, followed by bottom-up and genotypic effects in freshwater. Top-down processes are predicted to have strong effects on the likelihood of delayed maturation.     

Hepatic aryl hydrocarbon hydroxylase activities in coho salmon (Oncorhynchus kisutch) exposed to petroleum hydrocarbons

Coho salmon exposed to the water soluble fraction (WSF) of Cook Inlet crude oil for a maximum of 30 days showed a greater than three-fold increase in hepatic aryl hydrocarbon hydroxylase activity. The initial increase in enzyme activity appeared between 2 and 5 days of exposure and increased as a function of increased exposure time. Persistence of the induced enzyme activity was dependent on the length and the concentration of WSF exposure. Handling stress had no effect on the AHH activity, but starvation caused a decrease in the activity.     

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.     

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.     

Physiological parameters of growth in Saprolegnia parasitica coker

Persistent bacteria were separated fromS. parasitica by means of the oligodynamic effect of a silver ring in a modification ofRaper's technique. Inoculation of fungal cultures was by means of mycelial macerate. Growth was measured by mycelial dry weight. A chemically defined medium (standard medium) was developed which consisted of a mineral base (chlorides of magnesium, manganese, zinc, calcium, and iron) chelated with EDTA, supplemented with glucose, sodium glutamate, and methionine, and buffered at pH 7.0 with 0.01 M. KH₂PO₄. Shaking culture methods supported increased growth rates and higher dry weight yields compared to stationary methods. Excellent growth occurred between 15 to 30°C. in the standard medium and between pH 4.0 and 8.0 in the standard medium plus 0.01 M. sodium succinate and 0.01 M. TRIS used as additional buffers. Significant phosphate toxicity was demonstrated at concentrations exceeding 0.05 M. Sodium succinate and TRIS, used as buffers at 0.01 M. each, were compatible withS. parasitica, whereas boric acid, sodium barbital, and sodium citrate inhibited growth under similar conditions. Substitution of other carbon sources for glucose in the standard medium (on an equal carbon basis where possible) indicated that cellobiose, dextrin, fructose, glycerine, glycogen, sodium lactate, and soluble starch supported significantly heavier growth than did the standard medium minus glucose; glycogen had a greater yield than did the standard medium minus glucose; glycogen had a greater yield than the standard medium. Arabinose, dulcitol, galactose, inulin, lactose, mannitol, mannose, raffinose, rhamnose, sorbitol, sucrose, and xylose neither stimulated nor inhibited growth; however, growth inhibition was produced by α-ketoglutaric acid, sodium citrate, and sodium succinate. When fatty acids and lipids were substituted for glucose (on an equal carbon basis where possible), only butter, lard, oleo, and palmitic acid supported heavier growth ofS. parasitica than the standard medium minus glucose. Stearicacid neither stimulated nor inhibited growth; acetic acid, butyric acid, formic acid, octanoic acid, and propionic acid significantly inhibited the growth of the fungus. Various nitrogen sources were substituted for sodium glutamate in the standard medium (on an equal nitrogen basis where possible). Casein hydrolysate and gelatin produced yields higher than that developed in the standard medium; other nitrogen sources produced lesser yields but still greater than those from the standard medium minus sodium glutamate:

1. Alanine, arginine, aspartic acid, and histidine (good nitrogen sources).
2. Ammonium chloride, cysteine, leucine, serine, and urea (fair nitrogen sources).
3. Glycine, isoleucine, lysine, methionine, phenylalanine, potassium nitrate, sodium nitrate, threonine, tryptophan, and valine (poor nitrogen sources).

When various sulfur sources were substituted for methionine in the standard medium (on an equal sulfur basis), only cysteine and cystine produced dry weights comparable to that which developed in the standard medium. The following were very poor sulfur sources yet supported more growth than did the standard medium minus methionine: sodium sulfide, sodium thiosulfate, and thiourea. The ability of the other sulfur sources to support growth was questionable: potassium persulfate, sodium bisulfite, sodium dithionate, sodium hydrosulfite, sodium sulfate, sodium sulfite, and sodium thiocyanate. The standard medium contained only two nitrogen sources: sodium glutamate and methionine. Sodium glutamate served as a carbon source as well as a nitrogen source, but methionine could serve only as a source of sulfur.     

Mortality of coho salmon (Oncorhynchus kisutch) associated with burdens of multiple parasite species

Multiple analytical techniques were used to evaluate the impact of multiple parasite species on the mortality of threatened juvenile coho salmon (Oncorhynchus kisutch) from the West Fork Smith River, Oregon, USA. We also proposed a novel parsimonious mathematical representation of macroparasite distribution, congestion rate, which (i) is easier to use than traditional models, and (ii) is based on Malthusian parameters rather than probability theory. Heavy infections of Myxobolus insidiosus (Myxozoa) and metacercariae of Nanophyetus salmincola and Apophallus sp. occurred in parr (subyearlings) from the lower mainstem of this river collected in 2007 and 2008. Smolts (yearlings) collected in 2007–2010 always harboured fewer Apophallus sp. with host mortality recognised as a function of intensity for this parasite. Mean intensity of Apophallus sp. in lower mainstem parr was 753 per fish in 2007 and 856 per fish in 2008, while parr from the tributaries had a mean of only 37 or 13 parasites per fish, respectively. Mean intensity of this parasite in smolts ranged between 47 and 251 parasites per fish. Over-dispersion (variance to mean ratios) of Apophallus sp. was always lower in smolts compared with all parr combined or lower mainstem parr. Retrospective analysis based on smolt data using both the traditional negative binomial truncation technique and our proposed congestion rate model showed identical results. The estimated threshold level for mortality involving Apophallus sp. was at 400–500 parasites per fish using both analytical methods. Unique to this study, we documented the actual existence of these heavy infections prior to the predicted mortality. Most of the lower mainstem parr (approximately 75%) had infections above this level. Heavy infections of Apophallus sp. metacercariae may be an important contributing factor to the high over-wintering mortality previously reported for these fish that grow and develop in this section of the river. Analyses using the same methods for M.insidiosus and N. salmincola generally pointed to minimal parasite-associated mortality.     

Response of the interrenal to adrenocorticotropic hormone after short-term thyroxine treatment of coho salmon (Oncorhynchus kisutch)

The effects of experimentally elevated plasma thyroxine levels on the subsequent response of interrenals of coho salmon (Oncorhynchus kisutch) to adrenocorticotropic hormone (ACTH) in vitro were examined. Animals were treated with thyroxine by immersion (200 micrograms/L) for 3 days, which resulted in physiological elevations in circulating thyroxine. In animals treated before the parr-smolt transformation was completed (early smolts), thyroxine had no effect on plasma cortisol levels but significantly enhanced the sensitivity of the interrenal to ACTH in vitro. In animals treated after the period of smoltification (postsmolts), plasma cortisol levels were significantly higher than those of controls; both experimental and control animals had plasma cortisol levels higher than normally observed at this stage of development. The response of the interrenals of thyroxine-treated postsmolts to ACTH in vitro was significantly lower than that of controls. Results from the experiments using early smolts are in agreement with studies in other vertebrates showing that thyroid hormones are involved in maintaining the normal functioning of corticosteroidogenic tissue and suggest that thyroid hormones may be involved in the activation of the interrenal that occurs during smoltification. The results obtained using postsmolts are more difficult to interpret because of the possibility that these animals were physiologically stressed by the treatment. Increased ACTH release in vivo resulting from stress may have led to a depression of interrenal sensitivity to ACTH in vitro and may have masked a refractoriness of the pituitary-interrenal axis to thyroxine.     

An outbreak of myxobacterial disease in coho salmon (Oncorhynchus kisutch) reared in a Maine estuary

An epizootic of a myxobacterial infection in coho salmon (Oncorhynchus kisutch) was responsible for the death of 50,000 fish, 30% of the population. Cartiage in the nose, mouth and lower jaw was eroded, and yellow sheets of bacterial growth were observed in the mouth, pharynx and pneumatic duct. The severity of the disease increased with increasing water temperature. Pathogenicity trials were inconclusive; only two of 18 experimentally infected fish succumbed to the disease. However, the lesions, and the absence of other known pathogens suggests the myxobacterium was responsible.     

Genetics of size and growth rate through sexual maturity in freshwater-reared coho salmon (Oncorhynchus kisutch)

Genetic parameters of size through sexual maturity have been relatively unexplored for Pacific salmon. In this study, individually tagged coho salmon were raised in freshwater, and the heritabilities of size and growth rate were estimated at several intervals between 13 and 24 months of age (spawning). Heritability estimates for size were moderate to high from 13 to 19 months of age, ranging from 0.36 to 0.50, and lower from 21 months to spawning at 24 months, ranging from 0.17 to 0.32. Heritabilities of specific growth rates estimated over 3-month intervals were moderate from 16 to 21 months of age, ranging from 0.21 to 0.34. Genetic and phenotypic correlations between sizes measured at different ages were moderate to high, ranging from about 0.7 to 1.0. Correlations between growth rate and size indicated that the larger fish were the fastest growing between 16 and 19 months of age and were slower growing between 19 and 21 months of age.     

Parvicapsula minibicornis in anadromous sockeye (Oncorhynchus nerka) and coho (Oncorhynchus kisutch) salmon from tributaries of the Columbia River

The myxosporean parasite Parvicapsula minibicornis is described from adult sockeye and coho salmon during spawning migrations in tributaries of the Columbia River in Canada and the United States. These observations extend the known distribution of this parasite from the Fraser River drainage basin. The parasite was identified in Columbia River salmonids using polymerase chain reaction (PCR) and by in situ hybridization, but unlike in Fraser River salmon, it was not observed in conventional histological preparations of the kidney. Prevalence of the parasite determined by PCR was higher in spawning sockeye from the Fraser River than in those from the Okanagan River. Our ability to explain the relatively low prevalence and absence of clinical P. minibicornis infections in Columbia River salmon is hampered by our poor understanding of the life cycle of this parasite.     

Gonadal morphology of normal and sex-reversed triploid and gynogenetic diploid coho salmon (Oncorhynchus kisutch)

In this study, the gonadal morphology of untreated and sex-reversed juvenile triploid and gynogenetic diploid coho salmon was compared with that of diploids. Testes of triploids were of the same size as those of diploids. Spermatogonia, however, were significantly bigger than those of diptoids in both diameter (P<0·001) and volume (P<0·01), suggesting that this characteristic can be a useful indicator of ploidy in the early stages of gonadal development. In females, induction of triploidy did not affect the lamellar structure of the ovaries but reduced their size considerably. Further, these ovaries had no oocytes. Treatment of triploids with oestrogen resulted in the feminization of genotypic males, which had ovaries similar to those found in tripioid females. However, gonads of triploid males partially sex-re versed into females were identified by their enlargement, the presence of remnants of the male vascular system, and by the appearance of ovarian lacunae and germinal and somatic cells typical of triploid females, Induction of gynogenesis resulted in 100% females, of which 34% had ovaries of reduced size with areas devoid of oocytes. However, and contrary to what has been found in cyprinids, no male germ cells were observed in these ovaries. This discrepancy may reflect differences, in the mechanisms of sex determination between salmonids and cyprinids. Treatment of gynogenetics with androgen increased the number of fish with abnormal ovaries but also resulted in the production of phenotypic-male gynogenetic diploids, of which 11% had testes indistinguishable from those of untreated control diploids.