Growth estimates from otolith increment widths of juvenile chinook salmon (Oncorhynchus tshawytscha) reared in changing environments

For otolith increments to provide useful estimates of fish growth, otolith growth must covary closely with somatic growth. We reared groups of juvenile chinook salmon ( Oncorhynchus tshawytscha Walbaum) for 70 days, changing ration or temperature during a 20-day treatment period. Restricted rations halted somatic growth, however increment widths decreased gradually; somatic growth was overestimated from increment width. Otolith growth followed changes in water temperature more closely than changes in ration, supporting a hypothesized effect of metabolic rate on otolith growth. Increment growth was only loosely coupled to fish growth rate, and may also be affected by past growth histories. For juvenile fish, increment widths may not be sensitive indicators of short-term changes in growing conditions.     

Effect of actinomycin-D on gill Na+-K+ ATPase of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Actinomycin-D reduced gill Na⁺-K⁺ ATPase activity of chinook salmon Oncorhynchus ishawytswha (Walbaum), smolts and saltwater-adapted juveniles but had no significant effect on the enzyme activity of parr in fresh water. The similarity in response suggests that even though smolts are found in fresh water, their enzyme system is more characteristic of saltwater-adapted juveniles than freshwater-dwelling parr. A greater reduction in enzyme activity was found when fish were treated with actinomycin-D in salt water than in fresh water, suggesting that the enzyme degradation rate wasgreater in salt water than in fresh water.     

Maturation in chinook salmon, Oncorhynchus tshawytscha (Walbaum): early identification based on the development of a bimodal weight-frequency distribution

Male chinook salmon, orhynchus tshawytscha (Walbaum), are known to mature sexually after one summer in sea water, one year earlier than any of the females. Two year classes of first generation domestic chinook salmon stock reared to sexual maturity on a commercial salmon farm in British Columbia, Canada were sampled for wet weight at various times during the spring after their first winter in the sea. Frequency distributions of wet weight were developed for both year classes. The weight-frequency distributions for both cohorts became statistically bimodal in May of their first year in the sea. The fish from the two modal groups for both cohorts were sorted and kept separate over the summer. The difference in the mean weight for the two groups increased throughout the summer in both years. The higher weight group in each cohort proved to be >95% early maturing males, and represented 64–46% of all the early maturing males evident in the September following the sort. The potential use of this information for commercial salmon growers and fisheries scientists interested in sexual maturation of the chinook salmon is discussed.     

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.     

Molecular evolution at Mhc genes in two populations of chinook salmon Oncorhynchus tshawytscha

The DNA sequences of four exons of the MHC (major histocompatibilty complex) were examined in chinook salmon ( Oncorhynchus tshawytscha ) from an interior (Nechako River) and a coastal (Harrison River) population in the Fraser River drainage of British Columbia. Mhc class I A1, A2 and A3 sequences and a class II B1 sequence were obtained by PCR from each of 16–20 salmon from each population. The class I A1 and a pair of linked A2–A3 exons were derived from two different classical salmonid class I genes, Sasa-A and Onmy-UA , respectively. Allelic variation for B1, A1 and A2 was characterized by the high levels of nonsynonymous substitution indicative of the effects of natural selection on Mhc domains that contain peptide binding regions. The number of alleles detected at each of the four exons ranged from three ( B1 ) to 22 ( A1 ), but levels of nucleotide sequence divergence at all four exons were low relative to classical mammalian Mhc genes. The nucleotide similarity among alleles ranged between 89 and 99% over all exons, and all four domains possessed only two major sequence motifs. Allelic distributions at B1, A1 and A3 confirmed the genetic distinctiveness of the Harrison and Nechako chinook salmon populations revealed in previous studies. The two major allelic motifs of B1 and A1 segregated strongly between the populations. In spite of evidence that allelic diversity at these chinook salmon Mhc exons has been generated by selection, the level and distribution of diversity in the two salmon populations strongly reflected the demographic history of the species, which has been characterized by repeated bottlenecks and isolation-by-distance in glacial refugia.     

Prey naivety in the behavioural responses of juvenile Chinook salmon (Oncorhynchus tshawytscha) to an invasive predator

1. Non‐native predators might inflict proportionally higher mortality on prey that have no previous experience of them, compared to species that have coexisted with the predator for some time. 2. We tested whether juvenile Chinook salmon (Oncorhynchus tshawytscha) were less able to recognise a non‐native than a native predator, by investigating behavioural responses to the chemical cues of the invasive smallmouth bass (Micropterus dolomieu) and the native northern pikeminnow (Ptychocheilus oregonensis) in both laboratory and field experiments. 3. Laboratory results demonstrated strong innate antipredator responses of individual juvenile Chinook salmon to northern pikeminnow; fish spent 70% of time motionless and exhibited 100% greater panic response than in controls. By contrast, antipredator responses to the chemical cues of smallmouth bass did not differ from controls. 4. These results were supported by similar differences in recognition of these predator odours by groups of juvenile Chinook salmon in fully natural conditions, though responses reflected a greater range of antipredator behaviours by individuals. In field trials, responses to northern pikeminnow odour resulted in increased flight or absence, reductions in swimming and foraging, and increased time spent near the substratum, compared to smallmouth bass odour. 5. Given that survival of juvenile fish is facilitated by predator recognition, our results support the hypothesis that naivety may be an important factor determining the effect of non‐native predators on prey populations. Efforts to manage the effect of native and non‐native predators may benefit by considering complex behavioural interactions, such as these at the individual and group levels.     

Evolution of chinook salmon (Oncorhynchus tshawytscha) populations in New Zealand: pattern,rate, and process

Chinook salmon, Oncorhynchus tshawytscha, from the Sacramento River, California, USA were introduced to New Zealand between 1901 and 1907, and colonized most of their present-day range within about 10 years. The New Zealand populations now vary in phenotypic traits typically used to differentiate salmon populations within their natural range: growth in freshwater and at sea, age at maturity, dates of return to fresh water and reproduction, morphology, and reproductive allocation. This paper reviews a large research program designed to determine the relative contributions of phenotypic plasticity and genetic adaptation to this variation, in an effort to understand the processes underlying the natural evolution of new populations. We found strong evidence of trait divergence between populations within at most 30 generations, particularly in freshwater growth rate, date of return, and reproductive output, with plausible adaptive bases for these differences. Importantly, we also demonstrated not only a genetic basis for post-release survival but higher survival, and hence fitness, of a population released from its established site compared to another population released from the same site. We conclude that divergence of salmon in different rivers probably resulted initially from phenotypic plasticity (e.g., habitat-specific growth rates, and effects of upriver migration on ovarian investment). Philopatry (homing to natal streams) combined with rapid evolution of distinct breeding periods to restrict gene flow, facilitating divergence in other traits. We also suggest that in addition to genetic divergence resulting from random founder effects, divergence may also arise during the very early stages of colonization when the original colonists are a non-random, pre-adapted subset of the source population. This favored founders effect immediately improves the fitness of the new population. Overall, this research reveals the complex interplay of environmental and genetic controls over behavior, physiology and life history that characterize the early stages of population differentiation, a process that has taken place repeatedly during the history of salmon populations.     

Outbreaks of phaeohyphomycosis in the chinook salmon (Oncorhynchus tshawytscha) caused by Phoma herbarum

Phoma herbarum has been associated with two outbreaks of systemic mycosis in hatchery-reared chinook salmon (Oncorhynchus tshawytscha) fingerlings. Affected fish exhibited abnormal swimming behavior, exophthalmia, multiple rounded areas of muscle softening, protruded hemorrhagic vents, and abdominal swelling. In all affected fish, swimbladders were filled with whitish creamy viscous fungal mass, surrounded by dark red areas in swimbladder walls, kidneys, and musculature. Clinical and histopathological examinations suggest that the infection may have started primarily in the swimbladder and then spread to the kidneys, gastrointestinal tract, and surrounding musculature. Consistent microscopical findings included broad septate branched fungal hyaline hyphae, 5–12 μm in diameter within the swimbladder, stomach, and often within and adjacent to blood vessels. Profuse growths of woolly brown fungal colonies were obtained from swimbladders and kidneys on Sabouraud medium. On corn meal agar the formation of pycnidia, characteristic of Phoma spp., was detected within 10 days of incubation. Morphological and molecular analyses identified this fungus as Phoma herbarum. This report underscores systemic fungal infections as a threat to raceway-raised salmon.     

Diel feeding periodicity, daily ration and prey selection of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

The diel feeding periodicity, daily ration and prey selection of juvenile chinook salmon, Oncorhynchus tshawytscha , were studied in relation to the available prey. Maximum dry weight of food intake occurred about dawn, when mayflies were the major prey, but the greatest number of freshly eaten prey occurred during the afternoon, when chironomids and terrestrial dipterans predominated. Feeding activity at night was low, with smaller mayflies comprising up to 50% of the prey. During the day the young salmon fed selectively on chironomids and the larger mayflies, while trichopterans and terrestrial taxa were under-represented in the diet. Food consumption over the 24-h period averaged 8.3% of the fish dry body weight. Prey abundance in the drift explained about 50% of the composition of the diet. Although the fish selected larger mayflies, size apparently was not a main criterion for selection because chironomids, although smaller than mayflies, were also frequently eaten. Previous dietary experience of the fish and the diel pattern of prey abundance appear to best explain the selective feeding of juvenile chinook salmon.     

Prey preferences of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha

The diet of juvenile chinook salmon and the foods available to them were studied during spring and summer in a large, braided, New Zealand river. During both sampling periods fish and potential prey were collected at dawn and dusk. Analysis showed that in spring the feeding rate increased at dawn, when aquatic taxa comprised the majority of their prey. Prey of terrestrial origin dominated the diet at dusk in summer but formed only about 1% of the diet during spring, when few such prey were available.
During spring the fish selectively preyed upon larger nymphs of the mayflies Deleatidium spp. However, in summer chironomids, other dipterans, and trichopterans were consumed to the exclusion of Deleatidium . Most of the chironomids and trichopterans taken were pupae or emerging adults and it is suggested that this may reflect differences in vulnerability during the diurnal emergence period.     

A cobalt-lysine study of primary olfactory projections in king salmon fry (Oncorhynchus tshawytscha Walbaum)

Summary Primary olfactory projections in king salmon fry, Oncorhynchus tshawytscha, were studied with the cobaltlysine technique and after sectioning the entire head in a frozen state. The labeled axons can be traced from the olfactory epithelium, where cobalt was applied, into the olfactory bulb and to the ventral and lateral regions of the ventral telencephalon. The latter projection has not previously been reported, and may in actuality represent a transneuronal transport of cobalt. The terminations in the glomerular layer and in the external cellular layer of the bulb appear to be distributed differently in different parts of the bulb, suggesting regional specializations. A few neurons in the bulb were also always labeled suggesting that they may project to the olfactory epithelium.     

Ecomorphological plasticity of juvenile fall-run chinook salmon (Oncorhynchus tshawytscha) in perennial and ephemeral streams

Environmental Biology of Fishes - In the Central Valley of California, environmental characteristics differ between perennial and ephemeral stream types and therefore present different challenges...     

Behavioural thermoregulation and homing by spring chinook salmon, Oncorhynchus tshawytscha (Walbaum), in the Yakima River

Temperature-sensitive radio transmitters were employed to study the patterns of behavioural thermoregulation, habitat preference and movement of 19 adult spring chinook salmon, Oncurhynchus tshawytscha (Walbaum), in the Yakima River. During the 4 months prior to spawning, fish maintained an average internal temperature 2.5°C below ambient river temperature. This represented a 12 to 20% decrease in basal metabolic demand or a saving of 17.3 to 29.9 calkg⁻¹ h⁻¹. Fish were most commonly associated with islands, pools, and rock out-croppings along stream banks. Homing behaviour appeared to be modified to optimize temperature regimes and energy conservation. As the time of spawning approached, fish left thermal refuges and migrated to spawning grounds upstream and downstream of refuge areas. Although spring chinook salmon residing within cool-water refuges may be capable of mitigating sub-lethal temperature effects, cool-water areas need to be abundant and available to the fish. The availability of suitable thermal refuges and appropriate holding habitat within mainstem rivers may affect long-term population survival.     

Identification of the Y chromosome in chinook salmon (Oncorhynchus tshawytscha)

The Y chromosome in chinook salmon, Oncorhynchus tshawytscha, was identified using fluorescence in situ hybridization (FISH) with a probe to a male-specific repetitive sequence isolated from this species. The probe highlights the distal end of the short arm of an acrocentric chromosome with a DAPI-bright interstitial band of variable size. The proximal portion of the short arm of the Y chromosome contains 5S rDNA sequences, which are also found on the short arms of six other acrocentric chromosomes in this species.     

Food and growth of hatchery-produced chinook salmon, Oncorhynchus tshawytscha (Walbaum), in landlocked Lake Purrumbete, Victoria, Australia

One-year old hatchery-produced chinook salmon were released into landlocked Lake Purrumbete, Victoria, in 1976 and specimens were recaptured at three-monthly intervals during the next two years. Examination of their stomach contents revealed that fish, particularly Galaxias maculatus , formed the bulk of the food of the salmon. Other items eaten included Amphipoda, Cladocera, Ostracoda and Decapoda (Crustacea), Odonata, Coleoptera, Diptera, Trichoptera and Hemiptera (Insecta) and Gastropoda (Mollusca). At the end of their first three months in the lake the salmon had increased 85% in length and over 670% in weight. After two years in the lake, their length was 582 mm and their weight was 2.73 kg. Growth rate was lowest in spring when the relative amount of fish in the stomach contents was at its lowest and there was a greater diversity of food types in the dict.     

Chains of single-domain magnetite particles in chinook salmon,Oncorhynchus tshawytscha

Summary Although the presence of magnetite in their tissues is correlated with the ability of different species to detect magnetic fields, proof that the magnetite is involved in magnetoreception has not yet been provided. Using the approach employed to localize and isolate magnetic particles in the yellowfin tuna, we found that single-domain magnetite occurs in chains of particles in tissue contained within the dermethmoid cartilage of adult chinook salmon,Oncorhynchus tshawytscha. The particles are present in sufficient numbers to provide the adult fish with a very sensitive magnetoreceptor system. Magnetite in the chinook can be correlated with responses to magnetic fields in a congeneric species, the sockeye salmon. Based on the presence of the chains of particles, we propose behavioral experiments that exploit the responses of sockeye salmon fry to magnetic fields to test explicit predictions of the ferromagnetic magnetoreception hypothesis.     

In vitro detection of functional humoral immunocompetence in juvenile chinook salmon (Oncorhynchus tshawytscha) using flow cytometry

A flow cytometric (FCM) assay for detection of immunomodulatory effects of environmental factors on the humoral response of chinook salmon (Oncorhynchus tshawytscha) is described and validated. This technique combines exposure of whole animals or leucocyte cultures to immunomodulatory agents/conditions with in vitro mitogenic activation of B-lymphocytes. The proportion of leucocytes undergoing blastogenesis following in vitro stimulation with lipopolysaccharide (LPS) is quantified by FCM analysis of forward and side scatter properties. In addition, binding of a fluorescein isothiocyanate labelled anti-rainbow trout immunoglobulin M monoclonal antibody (anti-RBT SIgM-FITC), quantified by FCM analysis, is used to determine the ability of the lymphoblasts to express surface immunoglobulin M (SIgM).Through a series of calibration steps, it was confirmed that anti-RBT IgM-FITC was specific for B-lymphocyte SIgM in chinook salmon. Binding of anti-RBT IgM-FITC to chinook salmon SIgM positive leucocytes was effectively blocked with salmon serum and an isotype control was established. B-lymphocytes were partially removed from a population of leucocytes through adherence to a nylon wool column, which then demonstrated a consequent reduction in anti-RBT IgM-FITC binding. Using anti-RBT IgM-FITC as a marker, the distribution of resting lymphocytes expressing SIgM in lymphoid tissues of juvenile chinook salmon was described. The mean percentage of SIgM positive cells in spleen, pronephros and blood were found to be 62.1 (+/-2.82), 34.8 (+/-1.86) and 56.7% (+/-4.7) of all viable leucocytes, respectively. In a time-course experiment for optimal in vitro activation of leucocytes for this assay, blastogenesis and up-regulation of SIgM expression of splenic leucocytes were observed through FCM by 4 days post in vitro stimulation with LPS, continued through 7 days, but was no longer visible by 10 days post stimulation. Using this assay, reduced expression of SIgM in splenic and pronephric B-lymphocytes was detected following in vitro exposure to physiologically relevant stress concentrations of cortisol in conjunction with mitogenic stimulation. This technique will be a useful addition to the assays already available in the rapidly growing field of fish immunology.     

Isolation and characterization of a trypsin fraction from the pyloric ceca of chinook salmon (Oncorhynchus tshawytscha)

A trypsin fraction was isolated from the pyloric ceca of New Zealand farmed chinook salmon (Oncorhynchus tshawytscha) by ammonium sulfate fractionation, acetone precipitation and affinity chromatography. The chinook salmon enzyme hydrolyzed the trypsin-specific synthetic substrate benzoyl-dl-arginine-p-nitroanilide (dl-BAPNA), and was inhibited by the general serine protease inhibitor phenyl methyl sulfonyl fluoride (PMSF), and also by the specific trypsin inhibitors — soybean trypsin inhibitor (SBTI) and benzamidine. The enzyme was active over a broad pH range (from 7.5 to at least pH 10.0) at 25 °C and was stable from pH 4.0 to pH 10.0 when incubated at 20 °C, with a maximum at pH 8.0. The optimum temperature for the hydrolysis of dl-BAPNA by the chinook salmon enzyme was 60 °C, however, the enzyme was unstable at temperatures above 40 °C. The molecular mass of the chinook salmon trypsin was estimated as 28 kDa by SDS–PAGE.