The effect of substrate rearing on growth, aerobic scope and physiology of larval white sturgeon Acipenser transmontanus

The effect of substratum on growth and metabolic rate was assessed in larval white sturgeon Acipenser transmontanus. Yolk-sac larvae (YSL) were reared in bare tanks or tanks with gravel as substratum from hatch until approximately 16 days post hatch (dph). The effect of an artificial substratum was also evaluated on growth alone. Substratum had a significant effect on mass, with larvae reared in gravel and artificial substrata being larger than those reared without substratum. Routine metabolic rates were significantly lower and relative aerobic scope (the difference between maximum and routine metabolic rate) was significantly higher for YSL and feeding larvae (FL) reared in gravel relative to those reared in bare tanks, particularly before fish started feeding exogenously. Furthermore, gravel-reared larvae had higher whole-body glycogen concentrations relative to bare-tank-reared larvae. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) was relatively low in all treatments (< 1·7) indicating a limited ability to elevate metabolic rate above routine early in development and mass exponents for metabolic rate exceeded 1. Taken together, these data indicate that YSL reared without substratum may divert more of their energy to non-growth related processes impairing growth. This finding underscores the importance of adequate rearing substratum for growth of A. transmontanus and may provide support for habitat restoration and alternative hatchery rearing methods associated with sturgeon conservation.

Freshwater movement patterns by juvenile Pacific salmon Oncorhynchus spp. before they migrate to the ocean: Oh the places you'll go!

Juvenile movement patterns for coho salmon Oncorhynchus kisutch and Chinook salmon Oncorhynchus tshawytscha from two large interior rivers of British Columbia, Canada, were examined. Otoliths from post-spawned fishes were collected on spawning grounds and elemental signatures were determined through transects from sectioned otoliths using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Large variations in otolith elemental signatures were found during the freshwater life stage indicative of movement downstream to rivers and tributaries that differed in elemental signature. This study highlights that downstream movements occur before migration to the ocean during the parr-smolt transformation. Extensive downstream movements of parr appear to be a successful life-history strategy based on variations observed in the otolith elemental signatures of spawners. Movements downstream in parr and the remarkable homing ability of adults also suggest that imprinting to natal streams must occur prior to the parr-smolt transformation.

Physiological condition differentially affects the behavior and survival of two populations of sockeye salmon during their freshwater spawning migration

Recently, a segment of the Adams-Shuswap sockeye salmon (Oncorhynchus nerka) population initiated freshwater migration several weeks earlier than historically recorded, resulting in high mortality rates. The comigrating Chilko population maintained their historic river entry timing and did not experience elevated mortality. To test the hypothesis that population-specific differences in physiological condition would differentially influence behavior and survival when exposed to fisheries capture stress, we physiologically sampled individuals from both populations at the onset of the freshwater phase of their reproductive migration and tracked the remainder of their migrations using radio telemetry. Adams-Shuswap individuals had slower migration rates and were less likely to reach natal subwatersheds relative to Chilko individuals. Metabolic and osmoregulatory impairment was related to mortality for Adams-Shuswap individuals but not for Chilko individuals. Similarly, physiological condition correlated with migration rate for Adams-Shuswap but not Chilko fish. Survival to natal subwatersheds was 1.9 times higher for Chilko relative to Adams-Shuswap, a result that did not emerge until individuals approached natal subwatersheds several days after the stressor was applied. We conclude that physiological condition differentially affects the behavior and survival of these two populations, which may be a consequence of the early-entry phenomenon by a segment of the Adams-Shuswap population.

Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration

Since 1996, some populations of Fraser River sockeye salmon ( Oncorhynchus nerka Walbaum in Artedi, 1792) have begun spawning migrations weeks earlier than normal, and most perish en route as a result. We suspect that a high midsummer river temperature is the principal cause of mortality. We intercepted 100 sockeye during normal migration near a spawning stream and measured somatic energy and aspects of plasma biochemistry. Fish were then held at either 10 or 18 °C for 24 days. Before release, fish were biopsied again and implanted with acoustic transmitters. A group of biopsied but untreated control salmon were released at the same time. Sixty-two percent (8 of 13) of control salmon and 68% (21 of 31) of 10 °C salmon reached spawning areas. The 18 °C-treated fish were half as successful (35%; 6 of 17). During the holding period, mortality was 2 times higher and levels of Parvicapsula minibicornis (Kent, Whitaker and Dawe, 1997) infection were higher in the 18 °C-treated group than in the 10 °C-treated group. The only physiological difference between treatments was a change in gill Na+,K+-ATPase activity. This drop correlated negatively with travel times for the 18 °C-treated males. Reproductive-hormone levels and stress measures did not differ between treatments but showed significant correlations with individual travel times.

Dosage effects on heritability and maternal effects in diploid and triploid Chinook salmon (Oncorhynchus tshawytscha)

Induced triploidy (3N) in salmon results from a blockage of maternal meiosis II, and hence provides a unique opportunity to study dosage effects on phenotypic variance. Chinook salmon families were bred using a paternal half-sib breeding design (62 females and 31 males) and half of each resulting family was treated to induce triploidy. The paired families were used to test for dosage effects (resulting from triploidy) on (1) the distribution and magnitude of phenotypic variation, (2) narrow-sense heritability and (3) maternal effects in fitness-related traits (i.e., survival, size-at-age, relative growth rate and serum lysozyme activity). Quantitative genetic analyses were performed separately for diploid and triploid family groups. Triploidization resulted in significantly higher levels of phenotypic variance and substantial differences in patterns of variance distribution for growth and survival-related traits, although the patterns were reversed for lysozyme activity. Triploids exhibited higher narrow sense heritability values relative to diploid Chinook salmon. However, maternal effects estimates were generally lower in triploids than in diploids. Thus, the dosage effects resulting from adding an extra set of chromosomes to the Chinook salmon genome are primarily additive. Somewhat counterintuitively, however, the relative magnitude of the combined effects of dominance, epistasis and maternal effects is not affected by dosage. Our results indicate that inheritance of fitness-related quantitative traits is profoundly affected by dosage effects associated with induced triploidy, and that triploidization can result in unpredictable performance and fitness outcomes.

Ionoregulatory changes in different populations of maturing sockeye salmon Oncorhynchus nerka during ocean and river migration

We present the first data on changes in ionoregulatory physiology of maturing, migratory adult sockeye salmon Oncorhynchus nerka. Fraser River sockeye were intercepted in the ocean as far away as the Queen Charlotte Islands (approximately 850 km from the Fraser River) and during freshwater migration to the spawning grounds; for some populations this was a distance of over 700 km. Sockeye migrating in seawater toward the mouth of the Fraser River and upriver to spawning grounds showed a decline in gill Na+,K+-ATPase activity. As a result, gill Na+,K+-ATPase activity of fish arriving at the spawning grounds was significantly lower than values obtained from fish captured before entry into freshwater. Plasma osmolality and chloride levels also showed significant decreases from seawater values during the freshwater migration to spawning areas. Movement from seawater to freshwater increased mRNA expression of a freshwater-specific Na+,K+-ATPase isoform (alpha1a) while having no effect on the seawater-specific isoform (alpha1b). In addition, gill Na+,K+-ATPase activity generally increased in active spawners compared with unspawned fish on the spawning grounds and this was associated with a marked increase in Na+,K+-ATPase alpha1b mRNA. Increases in gill Na+,K+-ATPase activities observed in spawners suggests that the fish may be attempting to compensate for the osmotic perturbation associated with the decline in plasma chloride concentration and osmolality.

Routine and active metabolic rates of migrating adult wild sockeye salmon (Oncorhynchus nerka Walbaum) in seawater and freshwater

We present the first data on the differences in routine and active metabolic rates for sexually maturing migratory adult sockeye salmon (Oncorhynchus nerka) that were intercepted in the ocean and then held in either seawater or freshwater. Routine and active oxygen uptake rates (MO2) were significantly higher (27%-72%) in seawater than in freshwater at all swimming speeds except those approaching critical swimming speed. During a 45-min recovery period, the declining postexercise oxygen uptake remained 58%-73% higher in seawater than in freshwater. When fish performed a second swim test, active metabolic rates again remained 28%-81% higher for fish in seawater except at the critical swimming speed. Despite their differences in metabolic rates, fish in both seawater and freshwater could repeat the swim test and reach a similar maximum oxygen uptake and critical swimming speed as in the first swim test, even without restoring routine metabolic rate between swim tests. Thus, elevated MO2 related to either being in seawater as opposed to freshwater or not being fully recovered from previous exhaustive exercise did not present itself as a metabolic loading that limited either critical swimming performance or maximum MO2. The basis for the difference in metabolic rates of migratory sockeye salmon held in seawater and freshwater is uncertain, but it could include differences in states of nutrition, reproduction, and restlessness, as well as ionic differences. Regardless, this study elucidates some of the metabolic costs involved during the migration of adult salmon from seawater to freshwater, which may have applications for fisheries conservation and management models of energy use.

Heritability and Y-chromosome influence in the jack male life history of chinook salmon (Oncorhynchus tshawytscha)

Jacking in chinook salmon (Oncorhynchus tshawytscha) is an alternative reproductive strategy in which males sexually mature at least 1 year before other members of their year class. We characterize the genetic component of this reproductive strategy using two approaches; hormonal phenotypic sex manipulation, and a half-sib breeding experiment. We 'masculinized' chinook salmon larvae with testosterone, reared them to first maturation, identified jacks and immature males based on phenotype, and genotyped all fish as male ('XY') or female ('XX') using PCR-based Y-chromosome markers. The XY males had a much higher incidence of jacking than the XX males (30.8% vs 9.9%). There was no difference in body weight, gonad weight, and plasma concentrations of testosterone and 17beta-estradiol between the two jack genotypes, although XY jacks did have a higher gonadosomatic index (GSI) than XX jacks. In the second experiment, we bred chinook salmon in two modified half-sib mating designs, and scored the number of jacks and immature fish at first maturation. Heritability of jacking was estimated using two ANOVA models: dams nested within sires, and sires nested within dams with one-half of the half-sib families common to the two models. The sire component of the additive genetic variance yielded a high heritability estimate and was significantly higher than the dam component (h(2)(sire) = 0.62 +/- 0.21; h(2)(dam) = -0.14 +/- 0.12). Our experiments both indicated a strong sex-linked component (Y-chromosome) to jacking in chinook salmon, although evidence for at least some autosomal contribution was also observed.

The presence of high-affinity, low-capacity estradiol-17beta binding in rainbow trout scale indicates a possible endocrine route for the regulation of scale resorption

High-affinity, low-capacity estradiol-17beta (E(2)) binding is present in rainbow trout scale. The K(d) and B(max) of the scale E(2) binding are similar to those of the liver E(2) receptor (K(d) is 1.6 +/- 0.1 and 1.4 +/- 0.1 nM, and B(max) is 9.1 +/- 1.2 and 23. 1 +/- 2.2 fmol x mg protein(-1), for scale and liver, respectively), but different from those of the high-affinity, low-capacity E(2) binding in plasma (K(d) is 4.0 +/- 0.4 nM and B(max) is 625.4 +/- 63. 1 fmol x mg protein(-1)). The E(2) binding in scale was displaced by testosterone, but not by diethylstilbestrol. Hence, the ligand binding specificity is different from that of the previously characterized liver E(2) receptor, where E(2) is displaced by diethylstilbestrol, but not by testosterone. The putative scale E(2) receptor thus appears to bind both E(2) and testosterone, and it is proposed that the increased scale resorption observed during sexual maturation in both sexes of several salmonid species may be mediated by this receptor. No high-affinity, low-capacity E(2) binding could be detected in rainbow trout gill or skin.

Responsiveness of gill Na+/K+-ATPase to cortisol is related to gill corticosteroid receptor concentration in juvenile rainbow trout

A positive relationship between receptor concentration and tissue responsiveness is an often-assumed and rarely tested principle in endocrinology. In salmonids, seasonal changes in levels of plasma cortisol and gill corticosteroid receptors (CRs) during the spring indicate a potential role for this hormone in the parr-smolt transformation. It is not known whether these seasonal changes result in alterations in gill responsiveness to cortisol. The relationship between CR concentration and tissue responsiveness was, therefore, examined in the gills of juvenile rainbow trout (Oncorhynchus mykiss). Gill CR concentration (Bmax) and affinity (Kd) were assessed using a radioligand binding assay with the synthetic glucocorticoid triamcinolone acetonide. Gill responsiveness to cortisol was quantified by measuring in vitro Na+/K+-ATPase activity. Gill CR concentration was manipulated by stress or hormonal treatments. Repeated handling stresses resulted in a significant reduction in CR numbers. The decrease in CR Bmax corresponded to a reduction in gill responsiveness to cortisol. Triiodothyronine, but not growth hormone, treatment was found to increase CR Bmax significantly. The increase in CR numbers was correlated with a marked increase in gill responsiveness to cortisol. A significant positive linear relationship exists between the in vitro gill Na+/K+-ATPase activity response to cortisol and CR Bmax (r2=0.614, P&lt;0.001). We have demonstrated that binding sites for cortisol in the gills of rainbow trout have high affinity, high specificity and saturable binding and that the number of binding sites is correlated with the tissue response to cortisol.

Regulation of gill cytosolic corticosteroid receptors in juvenile Atlantic salmon: interaction effects of growth hormone with prolactin and triiodothyronine

The potential effects of growth hormone (GH), prolactin (Prl), and triiodothyronine (T3) on gill Na+,K+-ATPase activity and corticosteroid receptor (CR) concentration (Bmax) and dissociation constant (Kd) were examined in juvenile Atlantic salmon (Salmo salar). Compared to controls, fish injected with GH (ovine, 5.0 microgram g-1) had significantly greater gill Na+,K+-ATPase activity after 7 and 14 days. Gill CR Bmax and Kd were significantly elevated on day 7, but not day 14. T3 also significantly increased CR Bmax. The effect of GH on CR Bmax was also additive with T3 (5.0 microgram g-1) treatment. There was a synergistic effect on CR Bmax when purified coho salmon GH (csGH, 0.1 microgram g-1) was injected in combination with T3 (1.6 microgram g-1). Prl (ovine, 5.0 microgram g-1; purified coho salmon, 0.1 microgram g-1) did not significantly alter gill CR Bmax. Although Prl limited the increase in CR Bmax by GH, the effect was not signicant. T3 and Prl did not have an effect on Kd. GH significantly increased gill Na+,K+-ATPase activity, T3 administration did not have a significant effect, and Prl-treated fish had significantly lower gill Na+,K+-ATPase activity. The results indicate that T3 acts additively with GH, while Prl has no effect in regulating CR Bmax. An increase in cytosolic CR by GH and T3, but not Prl, may regulate gill responsiveness to cortisol and be an important mechanism in the endocrine control of physiological changes during the parr-smolt transformation.

Increases in gill cytosolic corticosteroid receptor abundance and saltwater tolerance in juvenile coho salmon (Oncorhynchus kisutch) treated with growth hormone and placental lactogen

Juvenile coho salmon (Oncorhynchus kisutch) were injected with one of two recombinant bovine hormones, growth hormone (bGH; 5.0 and 0.5 micrograms.g-1 body wt) or placental lactogen (bPL; 5.0, 0.5, and 0.05 micrograms.g-1 body wt) to determine the effect on growth, plasma cortisol concentration, cytosolic corticosteroid receptors (CR) in the gills, and the development of hypoosmoregulatory ability. One week following a single injection or six weekly injections of bGH or bPL, the fish were measured and sampled for CR concentration and Na+,K(+)-ATPase activity in the gills. Fish were also challenged with salt water (salinity 25%) for 24 hr to determine saltwater tolerance at the end of the 6-week treatment. Treatment with bPL and bGH significantly increased weight and length of the fish. The 0.05-micrograms bPL dose significantly elevated plasma cortisol concentration, whereas all other hormone treatments did not affect cortisol levels. bPL and bGH also significantly increased CR concentration and Na+,K(+)-ATPase activity in the gills. The perturbation in plasma sodium concentration was least in animals receiving the highest dose of bPL and the bGH-treated animals following transfer to seawater. An increase in cytosolic CR by bGH and bPL may increase responsiveness of the gills to cortisol and partially account for the increase in Na+,K(+)-ATPase activity and greater ability to regulate plasma sodium in seawater as exhibited by the experimental groups.

Downregulation of corticosteroid receptors in gills of coho salmon due to stress and cortisol treatment

The effect of stress and cortisol treatment on corticosteroid receptors (CRs) in the gills of coho salmon (Oncorhynchus kisutch) was examined. Plasma cortisol levels were elevated acutely by intraperitoneal injection of cortisol 21-hemisuccinate and chronically by implanting miniosmotic pumps filled with cortisol or by repeated daily handling stresses. CR concentration and affinity were measured by radioreceptor assay employing 3H-labeled triamcinolone acetonide as ligand. Acute administration of cortisol resulted in a reduction in CR numbers for 72 h with no change in affinity. Chronic cortisol treatment resulted in a decrease in CR concentration and affinity. The change in affinity occurred only while plasma cortisol levels remained elevated, but CR population remained significantly reduced for at least 10 days after cessation of hormone treatment. Repeated handling stresses resulted in a similar reduction in CR numbers but without an apparent change in affinity. The chronic or repeated elevation in plasma cortisol downregulates the sensitivity of the gills to cortisol by a persistent reduction in CR concentration, despite the return to nonstress levels of circulating cortisol.

Assessing the effects of positive buoyancy on rainbow trout (Oncorhynchus mykiss) held in gas supersaturated water

We examined the effects of swim bladder overinflation associated with dissolved gas supersaturation on rainbow trout (Oncorhynchus mykiss). The change in swim bladder volume with increased swim bladder pressure was measured in fish subjected to a decrease in ambient pressure. An expansion of swim bladder volume occurs that is related to the excess swim bladder pressure. The volume change results in a decrease in density and positive buoyancy in the fish. Small fish are adversely affected when exposed to gas supersaturated water because of the high swim bladder pressure required to force gas out the pneumatic duct. Changes in behaviour and depth distribution of fish held in gas supersaturated water were measured in a 2 m deep observation column. A large change in density caused small fish to increase depth and compensate for the swim bladder expansion. Although swim bladder inflation occurs for all sizes of trout held in gas supersaturated water, the impact is greatest for small fish and they must compensate by seeking depth. However, adequate depth to compensate for positive buoyancy may not always exist. In such a case, fish must swim continuously in a head down position to overcome excess buoyancy. The power necessary for a fish to swim with an overinflated swim bladder is greatest for small fish that show the largest change in density.

Factors affecting swim bladder volume in rainbow trout (Oncorhynchus mykiss) held in gas supersaturated water

We examined the response of the rainbow trout (Oncorhynchus mykiss) swim bladder to gas supersaturated water. Cannulas positioned in the swim bladder of fish were connected to a pressure transducer, allowing direct measurement of swim bladder pressure. When denied access to the surface, fish held in supersaurated water showed an increase in swim bladder pressure. This response showed a strong dependence on the total gas pressure and the oxygen partial pressure of the water. The minimum level of gas supersaturation observed to cause this response corresponds to a ΔP of 27 mmHg [Formula: see text]; 1 mmHg = 133.3 Pa). The threshold ΔP for swim bladder inflation increased as the partial pressure of dissolved oxygen increased. Movement of supersaturated gases from the arterial system into the swim bladder is passive and causes a rise in swim bladder pressure until the diffusion gradient is nil or the gas is expelled through the pneumatic duct. The threshold for release of gas out the pneumatic duct is dependent on the size of the fish. Small fish have higher duct release pressures and are subject to a higher degree of pressure buildup within the swim bladder than larger fish.