Effect of steroid hormones on the growth of juvenile coho salmon (Oncorhynchus kisutch)

Two androgens, 17 α-methyltestosterone and testosterone, and an estrogen, estradiol, were individually incorporated in test diets at 2.5 mg/kg dry diet and fed to coho salmon for 14 weeks. The fish weight gain, feed conversion efficiency, fish body composition and fatty acid composition of fish body lipids were determined. The three steroid hormones all accelerate the growth rate of fish. The 17 α-methyltestosterone supplementation promotes significantly greater fish weight gain and feed efficiency. Results of histologic examination of fish liver, kidney, heart, and gonad are discussed.     

Homing of coho salmon (Oncorhynchus kisutch) exposed to morpholine

Smolts of coho salmon (Oncorhynchus kisutch) were exposed to 5 × 10^?5 mg·l^?1 morpholine for 15 days and released into the Salmon River along with an unexposed control group. During the following two autumns, morpholine was introduced into the hatchery's fish ladder on various days and the return of experimental fish was recorded. The returns of morpholine-exposed and control fish were not statistically different. With morpholine present in the fish ladder, control fish were not repelled, and with morpholine absent from the ladder, morpholine-exposed fish returned as readily as control fish.     

Studies on the pathogenesis of vibriosis in coho salmon Oncorhynchus kisutch (Walbaum)

Abstract. Juvenile coho salmon Oncorhynchus kisutch (Walbaum), cultured in fresh water, were experimentally infected with highly virulent Vibrio anguillarum , and various haematological and biochemical parameters were compared between moribund and non-infected control fish. In addition, endotoxin, culture supernatant, and cell lysate preparations of V. anguillarum were tested separately and in combination to assess their roles in mediating pathological effects.
The haematocrit, haemoglobin, numbers of red and white blood cells and plasma, total protein, albumin, β₂ globulin, chloride, sodium, osmolality and alkaline phosphatase levels were all decreased in infected fish compared to controls. Erythrocyte fragility and plasma glucose, potassium, lactate dehydrogenase (LDH), and glutamic oxaloacetic transaminase (GOT) levels were increased in infected fish.
No mortality nor significant changes in haematocrit or plasma protein occurred in fish injected intraperitoneally with 35 mg/kg (1 mouse LD₅₀) of V. anguillarum endotoxin, with culture supernatant fluid, cell lysate, or with combinations of the three preparations. There was, however, a decrease in plasma protein concentration in coho injected with 355 mg/kg (10 mouse LD₅₀s) of endotoxin, but no mortality nor significant change in haematocrit.     

Increased ability to compete for food by growth hormone-transgenic coho salmon Oncorhynchus kisutch (Walbaum)

In salmonids, growth hormone (GH) stimulates growth, appetite and the ability to compete for food. This study tested the hypothesis that increased GH levels in GH-transgenic coho salmon Oncorhynchus kisutch (Walbaum) increase competitive ability through higher feeding motivation. The transgenic strain of salmon used contained a gene construct consisting of the sockeye metallothionein-B promoter fused to the type 1 growth gene coding region. The transgenic animals (mean size = 250 g) were F₁ individuals. In six consecutive feeding trials, the intake of contested food pellets by size-matched pairs consisting of one control (1 year older non-transgenic coho salmon) and one GH-transgenic coho salmon was compared. Pellets were provided sequentially until neither fish took three consecutive pellets; the identity of the fish taking each pellet was noted. Calculated on the three first pellets offered at each feeding trial, the transgenic coho salmon consumed 2.5 times more contested pellets than the controls, supporting the hypothesis that GH transgenesis increases the ability to compete for food. Overall, the transgenic fish consumed 2.9 times more pellets that the non-transgenic controls, indicating a high feeding motivation of the transgenic fish throughout the feeding trials. It appears that GH transgenesis and GH treatments can induce similar changes in the feeding behaviour of salmonids. Depending on how transgenic and wild individuals differ in other fitness-related characters, escaped GH transgenic fish may compete successfully with native fish in the wild.     

Genetic variability in four hatchery strains of coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

Coho salmon, Oncorhynchus kisutch (Walbaum), is intensively cultured in Chile. An increasing proportion of the eggs necessary to sustain the culture are locally produced by some hatcheries. However, there is no information about the origin or the genetic variability in these strains. The present study analysed allozymic variability and its distribution within and between some commercial strains of coho salmon in southern Chile. The genetic variability was estimated using horizontal starch gel electrophoresis. Samples of coho salmon were obtained randomly from four Chilean hatcheries. Twenty‐five enzymatic systems were examined, representing 51 enzymatic loci. Eight loci showed variability in at least one strain, which represented a total polymorphism (P) of 15.7%. Only the PGM‐1* locus was variable in all strains. The remaining loci were fixed in at least one strain. Total heterozygosity (H_T) and within population heterozygosity (H_S) were 0.35% and 0.36% respectively. The index of genetic diversity (G_ST) was 1.5%. The results confirm previous reports of low genetic variability in cultured strains of coho salmon in Chile, below that observed in their native range, which suggests loss of the genetic variability caused by genetic drift or other causes in these strains.     

Susceptibility of coho salmon, Oncorhynchus kisutch (Walbaum), to different toxins of Clostridium botulinum

Coho salmon Oncorhynchus kisutch (Walbaum), held at 15°C were tested for their susceptibility to toxins of proteolytic and nonproteolytic Clostridium botulinum types A, B, C₁, C₂, D, E, F, and G administered by the oral and intraperitoneal (i.p.) routes. By the oral route, the fish were most susceptibile to type E neurotoxin, which was lethal at a dose equivalent to 90 mouse intraperitoneal minimum lethal doses (MLDs). The oral lethal dose increased to 2000 MLD for nonproteolytic and proteolytic type F neurotoxins, but the toxin types A, B, and C₁ were not lethal to fish at 2000 MLD and type D was not lethal at 20 000 MLD (highest titre tested). The fish were not susceptible to 200 MLD (the highest titres tested) of type G neurotoxin or C₂ cytotoxin. By the i.p. route, all of the toxins except type G were lethal to coho salmon. Type E neurotoxin was the most toxic at a level of one‐half the mouse MLD. Coho salmon held at temperatures ranging from 1 to 20°C were sensitive to type E neurotoxin by both the oral and i.p. routes. As the temperature decreased the fish became more resistant to type E neurotoxin by the oral route, but the i.p. dose remained one‐half the mouse MLD at all temperatures.     

The toxicokinetics of benzo[a]pyrene in juvenile coho salmon, Oncorhynchus kisutch, during smoltification

The activities of Phase I and Phase II biotransformation enzymes in the livers of yearling coho salmon (Oncorhynchus kisutch), were measured biweekly from February until the release date from the hatchery in mid-June, in order to observe any alterations in baseline levels during smoltification. Peak enzyme activities occurred in February and March and then declined through to June. Total cytochrome P450 levels ranged from 0.024±0.009 to 0.095±0.010 nmol mg^-1 microsomal protein, ethoxyresorufin O-deethylase activity ranged from 2.74±0.75 to 9.94±0.85 pmol min^-1 mg^-1 microsomal protein, and glutathione S-transferase activity ranged from 0.07±0.01 to 0.33±0.01 μmol min^-1 mg^-1 cytosolic protein during this period. Following an intraperitoneal injection of [3H]benzo[a]pyrene (B[a]P), elimination occurred rapidly (>71% excreted into the bile within 24h) from February to June. Although the distribution of B[a]P in tissues changed through the sampling period, the highest leels of B[a]P-derived radioactivity were found in the liver, bile and fat. Analysis of the bile revealed that 55 to 63% of the radioactivity was Phase I metabolites, 16 to 24% glucuronide conjugates, 8% sulfate conjugates, 7% other conjugates and 6% aqueous-soluble metabolites. These findings suggest that the transformation from freshwater adapted coho ‘parr’ to ‘smolts’, can significantly alter biotransformation enzyme activities and the distribution and elimination of xenobiotics such as benzo[a]pyrene in these fish. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gene expression levels of growth hormone receptor and insulin-like growth factor-I in gonads of maturing coho salmon (Oncorhynchus kisutch)

The expression levels of growth hormone receptor (GHR) and insulin-like growth factor (IGF-I) in gonads of maturing coho salmon were measured by real-time PCR. The GHR and IGF-I mRNAs showed different gene expression pattern between male and female. These results suggest that a sexual dimorphism may exist in the GHR and IGF-I mRNA expressions of coho salmon during gonadal maturation     

Homing behaviour of juvenile coho salmon (Oncorhynchus kisutch) within an off-channel habitat

Abstract – Although homing behaviour has been observed in juvenile Atlantic salmon, brown trout and resident cutthroat trout, this behaviour has not been well studied in juvenile Pacific salmon. We examined the site fidelity and homing behaviour of juvenile coho salmon ( Oncorhynchus kisutch ) by marking and relocating them within an off-channel habitat. Over 80% of displaced fish returned to the area from which they were originally collected. The proportion of fish that returned to the original location did not vary significantly among three sampling dates. However, we found that this proportion decreased over time in a brackish lagoon when we statistically analysed the data reported by Day (1966) . Our results suggest that juvenile coho salmon exhibit strong site fidelity and are able to return to their home ranges after displacement. These behaviours are likely to be important for the winter survival of juvenile coho salmon.     

Effect of thyroid-stimulating hormone on the physiology and morphology of the thyroid gland in coho salmon,Oncorhynchus kisutch

Activity of the thyroid gland of the coho salmon,Oncorhynchus kisutch, was assessed by physiological, histological and ultrastructural criteria after treatment with graded doses of bovine thyrotropin (bTSH) in January and March. Average plasma thyroxine (T₄) levels increased from about 0.8 ng/ml in saline-injected controls to about 15 ng/ml in fish treated with four intraperitoneal injections of 0.8 lU bTSH. Light-microscope observations of one m-thick sections stained with methylene blue and azure II, showed that bTSH treatment increased epithelial height in both presmolts and smolts. Ultrastructural manifestations of increased activity owing to bTSH treatment were also seen, along with evidence of follicle proliferation. Cytoplasmic organelles and secretory granules increased in numbers with increased dosage of bTSH.     

Plasma somatolactin levels in coho salmon (Oncorhynchus kisutch) during smoltification and sexual maturation

Somatolactin (SL) is a novel pituitary hormone recently characterized in several fish species. Structural analyses have shown that SL belongs to the growth hormone/prolactin family, and that it is a highly conserved protein. SL is synthesized by the periodic acid/Schiff-positive cells in the pars intermedia, but has an as yet unidentified function(s). We have recently developed a homologous radioimmunoassay for coho salmon SL and measured plasma levels of SL during two stages of the coho salmon life cycle, smoltification and sexual maturation. During smoltification, plasma levels of SL changed almost in parallel with plasma levels of thyroxine; levels increased as morphological indices of smoltification appeared and decreased as smoltification was completed. Following this period, SL levels remained low until the spring prior to spawning. In a separate study, plasma levels of SL were measured in sexually maturing coho salmon that remained in fresh water throughout their life cycle. During the year of sexual maturation, plasma levels of SL gradually increased from the spring onward, reaching peak levels at the time of spawning in November and December. These data are similar to those previously reported for sexually maturing coho salmon that were maintained in seawater prior to spawning (Rand-Weaver et al. 1992). Therefore, increases in plasma SL levels occurred in sexually maturing fish irrespective of whether they were maintained in fresh water or seawater. Peak levels at spawning were higher than those observed during smoltification. Possible roles for SL in metabolism and reproduction are discussed.     

Climate variability and marine survival of coho salmon (Oncorhynchus kisutch) in the Oregon production area

Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970–94) and marine survival of hatchery-reared coho salmon from California to Washington (1960–94) are significantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is significantly and independently related to the dominant modes acting over this region in the periods when the coho first enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set.     

Marine environment‐based forecasting of coho salmon (Oncorhynchus kisutch) adult recruitment

Generalized additive models (GAMs) were used to investigate the relationships between annual recruitment of natural coho salmon (Oncorhynchus kisutch) from Oregon coastal rivers and indices of the physical ocean environment. Nine indices were examined, ranging from large‐scale ocean indicators, e.g., Pacific Decadal Oscillation (PDO), to indicators of the local ecosystem (e.g., coastal water temperature near Charleston, OR). Generalized additive models with two and three predictor variables were evaluated using a set of performance metrics aimed at quantifying model skill in short‐term (approximately 1 yr) forecasting. High explanatory power and promising forecast skill resulted when the spring/summer PDO averaged over the 4 yr prior to the return year was used to explain a low‐frequency (multi‐year) pattern in recruitment and one or two additional variables accounted for year‐to‐year deviations from the low‐frequency pattern. More variance was explained when averaging the predictions from a set of models (i.e., taking the ensemble mean) than by any single model. Making multiple forecasts from a set of models also provided a range of possible outcomes that reflected, to some degree, the uncertainty in our understanding of how salmon productivity is driven by physical ocean conditions.     

Infectious haemolytic anaemia causes jaundice outbreaks in seawater-cultured coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

In the last 9 years, epizootics of an icterus condition has affected coho salmon, Oncorhynchus kisutch (Walbaum), reared in seawater cages in southern regions of Chile. At necropsy, fish from field cases exhibited signs of jaundice accompanied by pale light-brown livers and dark spleens. Histopathological and haematological results indicated that these fish presented haemolytic anaemia. After microbiological examination no bacterial or viral agents could be identified as aetiological agents of this disease. In an infectivity trial, coho salmon, Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), were inoculated intraperitoneally with a filtrate of an organ homogenate (0.45 microm) from a diseased coho salmon and held for 60 days in tanks supplied with fresh water. The disease was only reproduced in coho salmon in which mortalities, beginning at day 23 post-inoculation (p.i.), reached a cumulative value of 24% at day 27 p.i. This condition was transmitted to non-inoculated cohabiting coho salmon suggesting that it is a waterborne disease. Thus, this icteric condition is caused by an infectious form of haemolytic anaemia, probably of viral aetiology, and coho salmon are more susceptible than either Atlantic salmon or rainbow trout.     

Modelling the reestablishment of coho salmon (Oncorhynchus kisutch) in Klamath River tributaries after dam removal

The planned removal of four dams on the Klamath River (anticipated 2024) will be the largest river restoration effort ever undertaken on the planet. Dam removal will restore access to >50 km of the Klamath River mainstem for coho salmon, but mainstem habitat may not be suitable for rearing juvenile coho salmon. Instead, small tributaries may provide most rearing habitat for reestablishing coho salmon. We used four approaches to evaluate six Klamath River tributaries above existing dams to assess their potential to support juvenile coho salmon: (1) We measured summer temperature regimes and evaluated thermal suitability. (2) We applied an Intrinsic Potential (IP) model to evaluate large-scale geomorphological constraints on coho salmon habitat. (3) We used the Habitat Limiting Factors Model (HLFM) to estimate rearing capacity for juveniles given current habitat conditions. (4) We developed an occupancy model using data from reference tributaries to predict coho salmon rearing distribution. All six streams had summer temperatures cooler than the mainstem Klamath River. However, five of the streams have barriers that will restrict coho salmon to within 5 km of the confluence with the Klamath River and two were disconnected mid-summer. Despite these constraints, the tributaries will likely produce coho salmon. Most streams had high IP in their lower reaches, the HLFM model estimated a total capacity of 105,000 juvenile coho salmon, and the occupancy model predicted juvenile coho salmon will rear throughout the accessible reaches. Protection and habitat enhancement for these tributaries will be important for coho salmon reestablishment post-dam removal.     

Propylthiouracil-induced hypothyroidism in coho salmon, Oncorhynchus kisutch: effects on plasma total thyroxine, total triiodothyronine, free thyroxine, and growth hormone

Thyroid hormones transiently increase during parr-smolt transformation in coho salmon, Oncorhynchus kisutch, and are believed to trigger morphological, physiological, behavioural, and neural changes. The effectiveness of propylthiouracil (PTU) to induce hypothyroidism in smolting coho salmon was determined by immersing coho salmon, Oncorhynchus kisutch, in 30 mg l–1 PTU from May 1, two weeks prior to the consistent annual total thyroxine (TT4) peak in mid-May, until the last sampling date. Plasma was obtained at two sampling dates from control and PTU -treated coho salmon: May 15, during the plasma TT4 peak; and May 26, after the TT4 peak. Radioimmunoassays were used to measure plasma TT4, total triiodothyronine (TT3), free thyroxine (FT4), and salmon growth hormone (sGH). The PTU -treatment inhibited the natural smoltification-related increases in plasma TT4, TT3 and GH levels compared with controls, but PTU-treatment did not affect these hormone levels when they were low. PTU -treatment increased FT4 and decreased TT3 and sGH levels in the May 26 sample. In the May 15 sample, FT4 levels were unaffected by PTU-treatment, whereas TT4 levels were decreased. These data demonstrate the ability of PTU to induce hypothyroidism in salmonids as shown by the decrease in TT4 and TT3. These data demonstrate that PTU treatment by immersion can induce hypothyroidism in salmonids as shown by: (1) the inhibition of the natural increases of TT4 and TT3; (2) the increase in FT4 levels corresponding to the lowered TT3 levels, suggesting an inhibition of thyroxine 5-monodeiodinase activity. We also show for the first time that PTU treatment can lower plasma GH levels in salmonids. This lowering of plasma GH level is associated with the decrease in TT3 levels and the increase in FT4 levels. The PTU induced lowering in GH levels may contribute to the observed changes in FT4 and TT3, since GH is known to increase thyroxine 5-monodeiodinase activity.     

Interactions between novel water,thyroxine and olfactory imprinting in underyearling coho salmon,Oncorhynchus kisutch (Walbaum)

Experimental evidence suggests that olfactory imprinting by salmon occurs during a sensitive period associated with surges in plasma thyroxine (T4) levels during smolting. Life-history studies, however, suggest that imprinting may occur prior to smolting. A possible resolution of this paradox may lie in the finding that exposure of coho salmon, Oncorhynchus kisutch (Walbaum) smolts to novel water sources induced transient increases in plasma T4 levels. If novel water-induced T4 surges occur prior to smolting and T4 surges are required for olfactory imprinting, juvenile salmon experiencing novel water sources as they move through their watershed may learn olfactory waypoints (e.g. stream confluences). To test this hypothesis, we exposed subyearling coho salmon, Oncorhynchus kisutch (Walbaum), to novel odours or water sources at distinct developmental stages. Subyearlings did not demonstrate dramatic increases in plasma T4 levels during smolting and exposure to novel water sources also had no effect on basal T4 levels. Previous studies have indicated that such coho smolts successfully imprint to similar exposure paradigms and home accurately. These results suggest that surges in plasma T4 levels during smolting may not be necessary for olfactory imprinting and accurate homing.     

The effect of temperature on agglutination activity of coho salmon Oncorhynchus kisutch (Walbaum) antiserum

Abstract. The effects of temperature on the activity of antisera from coho salmon ( oncorhynchus kisutch ) and from rabbit were compared. Agglutination activity of salmon anti-Aeromonas salmonicida serum declined following incubation at 55°C whereas rabbit antiserum lost agglutination activity after incubation at 65°C.     

Relationship between fish growth rate and progression of artificially induced erythrocytic inclusion body syndrome in coho salmon, Oncorhynchus kisutch (Walbaum)

Abstract. Studies were conducted to clarify the relationship between growth rate and disease progression of erythrocytic inclusion body syndrome (EIBS) in artificially infected coho salmon, Oncorhynchus kisutch (Walbaum). In the diseased state, the haematocrit values decreased and the number of erythrocytes with inclusions was higher in faster growing fish. Rapid growth was accompanied by an abundance of immature erythrocytes, which had the greatest incidence of inclusion bodies.