Observations on saprolegniasis of adult sockeye salmon, Oncorhynchus nerka (Walbaum)

Some observations on the mycology and pathology of saprolegniasis of maturing sockeye salmon are reported. Saprolegnia spp. were isolated from all lesions examined. Some isolates did not produce oogonia and could not be identified further. The other isolates have affinities to the S. diclina-S. parasitica complex. Observations on the gross and histo-pathology of the lesions show the fungi can be active pathogens. It is hypothesized that increased levels of plasma corticosteroids and depletion of ascorbic acid reserves in the fish increase the probability that Saprolegnia spp. will initiate infections, either alone or concurrently with other opportunistic parasites.     

The effects of low pH on egg and alevin survival of kokanee and sockeye salmon, Oncorhynchus nerka

1. The effects of low pH water on embryogenesis and vitellogenesis in kokanee and sockeye salmon (Oncorhynchus nerka) were investigated. Eggs were exposed to low pH from fertilization to 45 days post-median hatch or to an episodic exposure at pH 4.0. Adult kokanee were also exposed to low pH just prior to ovulation and spawning. 2. The most sensitive stages of development during chronic or episodic exposure to low pH were early embryonic development and newly-hatched alevins. 3. Incubation of eggs at low pH caused a lower median survival, delayed hatching, higher alevin mortality and reduced the efficiency of yolk conversion to tissue of yolk-sac alevins. Those effects were more pronounced when the eggs were fertilized at low pH. 4. Exposure of sexually mature kokanee salmon to acidified water reduced egg and alevin survival, delayed embryo hatching and decreased the percent hatch. Those effects were more pronounced when their eggs were incubated at low pH.     

Compensatory swimming in the kokanee and sockeye salmon Oncorhynchus nerka (Walbaum)

When negatively buoyant, such as by increased pressure or loss of swimbladder gas, kokanee and sockeye salmon ( Oncorhynchus nerka ) attempt to swim upward by increased use of the pectoral fins. This response is termed compensatory swimming. Prior to initial filling of the swimbladder, sockeye fry showed no behavioural response to pressures above atmospheric. Following air-gulping at the surface and bladder inflation, kokanee and sockeye fry responded to increased pressure by assuming a more vertical position and by beating the pectoral fins more rapidly. In young sockeye this response occurred over the pressure range of atmospheric to 20 lb/in², and the effect of this behaviour would be to distribute these fish in the upper 14 m of the lacustrine environment. Fingerling kokanee showed a more gradual increase in compensatory swimming over the range of pressure equivalent to depths of 0–50 m. The behaviour of yearling kokanee would tend to concentrate these fish in the upper 30 m. Sockeye older than 1 year responded to negative buoyancy with increased horizontal swimming whilst planing upward on the pectoral fins. Depth distribution postulated on the basis of pressure-induced compensatory swimming is consistent with the known vertical distribution of kokanee and sockeye salmon.     

Host-pathogen-environment interactions predict survival outcomes of adult sockeye salmon (Oncorhynchus nerka) released from fisheries

Incorporating host-pathogen(s)-environment axes into management and conservation planning is critical to preserving species in a warming climate. However, the role pathogens play in host stress resilience remains largely unexplored in wild animal populations. We experimentally characterized how independent and cumulative stressors (fisheries handling, high water temperature) and natural infections affected the health and longevity of released wild adult sockeye salmon (Oncorhynchus nerka) in British Columbia, Canada. Returning adults were collected before and after entering the Fraser River, yielding marine- and river-collected groups, respectively (N = 185). Fish were exposed to a mild (seine) or severe (gill net) fishery treatment at collection, and then held in flow-through freshwater tanks for up to four weeks at historical (14°C) or projected migration temperatures (18°C). Using weekly nonlethal gill biopsies and high-throughput qPCR, we quantified loads of up to 46 pathogens with host stress and immune gene expression. Marine-collected fish had less severe infections than river-collected fish, a short migration distance (100 km, 5–7 days) that produced profound infection differences. At 14°C, river-collected fish survived 1–2 weeks less than marine-collected fish. All fish held at 18°C died within 4 weeks unless they experienced minimal handling. Gene expression correlated with infections in river-collected fish, while marine-collected fish were more stressor-responsive. Cumulative stressors were detrimental regardless of infections or collection location, probably due to extreme physiological disturbance. Because river-derived infections correlated with single stressor responses, river entry probably decreases stressor resilience of adult salmon by altering both physiology and pathogen burdens, which redirect host responses toward disease resistance.     

Persistent parental effects on the survival and size, but not burst swimming performance of juvenile sockeye salmon Oncorhynchus nerka

Sockeye salmon Oncorhynchus nerka were used as a model in an artificial fertilization experiment to investigate the relationships between individual adult O. nerka and their offspring. Survival, size and burst swimming ability were assessed in fry of known parentage (adult spawners from the Weaver Creek population, British Columbia, Canada). Maternal identity significantly affected the survival rate of eggs at hatch time, though this effect did not extend to fry life stages. The results were also suggestive of a paternal effect on both egg and fry survival, though this could not be separated from the experimental block design. After 4 months of exogenous feeding, fry mass remained under significant maternal influence, though fork length did not, despite having a high correlation with mass. Burst swimming performance was highly variable among individuals, and was not significantly influenced by maternal identity or individual fry size. Collectively, the findings presented here suggest that maternal, and possibly paternal, effects can be integral components of population dynamics in the early life stages of O. nerka . A good understanding of these factors will be essential for scientists and fisheries managers in developing a more holistic view of population-level spawning success and fry survival.     

Effects of rearing temperature on immune functions in sockeye salmon (Oncorhynchus nerka)

To determine if the defences of sockeye salmon (Oncorhynchus nerka) raised in captivity are affected by the rearing temperature or their life-cycle stage, various indices of the humoral and cellular immune functions were measured in fish reared at either 8 or 12 degrees C for their entire life-cycle. Measures of humoral immunity included the commonly used haematological parameters, as well as measurements of complement, and lysozyme activity. Cellular assays quantified the ability of macrophages from the anterior kidney to phagocytise Staphylococcus aureus cells, or the activities of certain bactericidal systems of those cells. The T-dependent antibody response to a recombinant 57 kDa protein of Renibacterium salmoninarum was used to quantify the specific immune response. Fish were sampled during the spring and fall of their second, third and fourth years, corresponding to a period that began just before smolting and ended at sexual maturation. Fish reared at 8 degrees C tended to have a greater percentage of phagocytic kidney macrophages during the first 2 years of sampling than the fish reared at 12 degrees C. During the last half of the study the complement activity of the fish reared at 8 degrees C was greater than that of the 12 degrees C fish. Conversely, a greater proportion of the blood leucocytes were lymphocytes in fish reared at 12 degrees C compared to the fish reared at 8 degrees C. Fish reared at 12 degrees C also produced a greater antibody response than those reared at 8 degrees C. Results suggested that the immune apparatus of sockeye salmon reared at 8 degrees C relied more heavily on the non-specific immune response, while the specific immune response was used to a greater extent when the fish were reared at 12 degrees C. Although a seasonal effect was not detected in any of the indices measured, varying effects were observed in some measurements during sexual maturation of fish in both temperature groups. At that time there were dramatic decreases in complement activity and lymphocyte numbers. This study was unique in its scope because it was the first quantitative assessment of salmon immune functions for an entire life-cycle.     

Fine structure of the adenohypophysis in immature sockeye salmon,Oncorhynchus nerka

Summary The ultrastructure of the secretory cells of the adenohypophysis of juvenile sockeye salmon was investigated. Pituitary glands were collected from immature fish transferred experimentally to sea water and subsequently returned to fresh water. The rostral pars distalis contained three cell types: ACTH cells, prolactin cells, and non-secretory cells. The prolactin and non-secretory cells were joined together in the form of follicles by desmosomes and they both had cilia and microvilli projecting into the follicle lumen. Various follicular structures such as lumen, multivesicular structures, and peripheral basement membrane are discussed as possible sites of prolactin cell granule release. The columnar ACTH cells were found at the junction of the rostral pars distalis and the neurohypophysis. The cytoplasmic granules in these cells were characteristically separated from their limiting membrane by a clear space. Multivesicular structures were also found in association with this cell type. The caudal pars distalis also contained three cell types: one acidophil (putative somatotrop) and two basophils (putative thyrotrops and gonadotrops), all of which were similar to those described in adult fish. The pars intermedia contained only one cell type. They appeared to be active cells and were characterized by containing membrane-bounded granules similar to those found in the ACTH cells. Changes in ambient salinity had no apparent effect on any cell type described.The work was supported by a grant in aid of research from the National Research Council of Canada. We wish to thank Mr. R. Lindsay, Mr. C. Cooper, and Mr. G. Longworth for their technical assistance. We would also like to thank Mr. S. Killick of the International Pacific Salmon Fisheries Commission for his assistance in the collection of fish and Dr. H. Cook for his helpful discussion of the project. This paper is No. 058 in the University of Guelph Migration Series.     

Genetic differentiation of sockeye salmon Oncorhynchus nerka (Walbaum, 1792) populations of eastern Kamchatka

The interpopulation differentiation of the sockeye salmon Oncorhynchus nerka (Walbaum) from the Olyutorskiy and Karaginskiy districts and from the Kamchatka River basin was examined based on the allelic variation at eight microsatellite loci (Ots107, Oki1a, Oki1b, One104, One109, OtsG68, OtsG85, and Oki6). The genetic diversity of samples from the northern rivers was lower, compared to samples from the Kamchatka River basin. Significant heterogeneity was found in the allele-frequency distribution at microsatellite loci of sockeye salmon from the investigated localities. The degree of genetic similarity of populations corresponded to their geographic closeness. The differences between population groups greatly exceeded the level of interpopulation differentiation. The analyzed samples formed four relatively separate groups: Lake Azabachye, Kamchatka River basin, Karaginskiy area (including the Navyrinvayam River in the south of the Olyutorskiy district), and northern Olyutorskiy area. The identification likelihood estimates of eastern Kamchatkan sockeye salmon in mixed aggregations at the level of population groups were fairly high (67.2–81.8%), greatly exceeding the accuracy of identification of individual populations.     

Two differing salmon GnRH precursor mRNAs are co-expressed in the brain of sockeye salmon (Oncorhynchus nerka)

The localization of two salmon-type gonadotropin-releasing hormone (sGnRH) precursors, pro-sGnRH-I (short type) and pro-sGnRH-II (long type), was investigated by using in situ hybridization techniques in the brain of the landlocked sockeye salmon, Oncorhynchus nerka. We used 30-mer oligonucleotide probes complementary to pro-sGnRH-I and pro-sGnRH-II cDNA. No significant differences were observed in the localization of sGnRH neurons expressing pro-sGnRH-I and pro-sGnRH-II mRNAs; both were expressed in the olfactory nerve, the olfactory bulbs, the regions between the olfactory bulb and telencephalon, the ventral telencephalon, the preoptic area, and the hypothalamus. Almost all sGnRH neurons examined co-expressed both precursors. The expression of two sGnRH precursors in the same neuron and the wide distribution of such neurons in the brain suggest that there are no functional differences between the two precursors.     

Assignment of sockeye salmon (Oncorhynchus nerka) to spawning sites using DNA markers

Randomly amplified polymorphic DNA (RAPD) markers were used to assign individual adult sockeye salmon to their spawning sites using a genotype assignment test. Six primers were selected for use by screening bulked DNA samples for markers missing in fish from one or more of 5 sites in British Columbia or Alaska. Of 73 markers scored, 54 showed variation between or within sites among the sampled fish. Thirty-seven of the variable markers were not detected in any fish from one or more sites; 18 variable markers were detected in all fish from one or more other sites. Thus 25% of markers scored were found in all fish of some sites and in no fish of some other sites. An assignment test placed all 70 fish tested into their correct populations. Principal coordinate analysis of genetic variation produced clusters of fish corresponding to each sampling site. No sex-specific RAPD markers were detected among more than 1300 screened.     

Adrenocorticotropin- and opiate-like hormones from pituitaries of the sockeye salmon Oncorhynchus nerka

The pituitaries of vitellogenic sockeye salmon (Oncorhynchus nerka) were extracted with a mixture of acetone, water, and hydrochloric acid. The precipitate which formed upon the addition of a copious volume of acetone to the extract, designated acid acetone powder, was subjected to salt fractionation and desalting, followed by ion-exchange chromatography on CM-cellulose. An unadsorbed fraction (S-1) and four adsorbed fractions (S-2, S-3, S-4 and S-5) were obtained. Adrenocorticotropic activity was detected in the fractions by their ability to stimulate isolated rat adrenal decapsular cells to produce corticosterone and by their immunoreactivities in an adrenocorticotropin-specific radioimmunoassay. The steroidogenic activities of all fractions, except S-4, were blocked by corticotropin inhibiting peptide. Opiate activity was detected in the fractions by their ability to inhibit the binding of either [3H]naloxone or (D-ala2, D-leu5)-[3H]enkephalin to rat brain membranes. There was a discrepancy in the potencies of the five fractions in the two opiate radioreceptor assays, indicating the presence of opiate peptides with different affinities of binding to the micron- and delta-opiate receptors of the rat brain. There was a separation between adrenocorticotropic and opiate receptor binding activities, suggesting that the activities were due to separate molecular entities.     

Juvenile habitat partitioning and relative productivity in allochronically isolated sockeye salmon (Oncorhynchus nerka)

Allochronic divergence, like spatial isolation, may contribute to population diversity and adaptation, however the challenges for tracking habitat utilization in shared environments are far greater. Adult Klukshu River (Yukon, Canada) sockeye salmon, Oncorhynchus nerka, return as genetically distinct "early" and "late" runs. Early and late adult spawning populations (1999 and 2000) and their subsequent fry (sampled at 7 sites in 2000 and at 8 sites in 2001 throughout Klukshu Lake and River) were genotyped at eight microsatellite loci. Bayesian assignment was used to determine the spatial distribution of early versus late fry; although intermixed, the distribution of fry significantly differed in Klukshu Lake and in the Klukshu River in 2001, based on crosstab analyses. Late-run fry predominated in Klukshu Lake at all sites, while early-run fry were most common in the north and south of Klukshu Lake and in Klukshu River. Early-run spawners had significantly higher relative productivity (early life survival) than late-run fish (2.9 times more fry produced per early-run adult in 2000, and 9.2 times more in 2001). This study demonstrates spatial habitat partitioning and differences in the contribution of allochronically isolated populations to fry abundance, and highlights annual variability that likely contributes to recruitment variation.     

Ontogenetic shifts in olfactory rosette morphology of the sockeye salmon,Oncorhynchus nerka

Sockeye salmon, Oncorhynchus nerka, are anadromous, semelparous fish that breed in freshwater—typically in streams, and juveniles in most populations feed in lakes for 1 or 2 years, then migrate to sea to feed for 2 or 3 additional years, before returning to their natal sites to spawn and die. This species undergoes important changes in behavior, habitat, and morphology through these multiple life history stages. However, the sensory systems that mediate these migratory patterns are not fully understood, and few studies have explored changes in sensory function and specialization throughout ontogeny. This study investigates changes in the olfactory rosette of sockeye salmon across four different life stages (fry, parr, smolt, and adult). Development of the olfactory rosette was assessed by comparing total rosette size (RS), lamellae number, and lamellae complexity from scanning electron microscopy images across life stages, as a proxy for olfactory capacity. Olfactory RS increased linearly with lamellae number and body size (p < .001). The complexity of the rosette, including the distribution of sensory and nonsensory epithelia and the appearance of secondary lamellar folding, varied between fry and adult life stages. These differences in epithelial structure may indicate variation in odor-processing capacity between juveniles imprinting on their natal stream and adults using those odor memories in the final stages of homing to natal breeding sites. These findings improve our understanding of the development of the olfactory system throughout life in this species, highlighting that ontogenetic shifts in behavior and habitat may coincide with shifts in nervous system development.     

Microsatellite DNA variation in sockeye salmon Oncorhynchus nerka (Walbaum, 1792) populations of eastern Kamchatka

The allelic variations of eight microsatellite loci (Ots107, Oki1a, Oki1b, One104, One109, OtsG68, OtsG85, and Oki6) were examined in sockeye salmon Oncorhynchus nerka (Walbaum) populations of eastern Kamchatka. Samples from river basins of the Karaginskiy and Olyutorskiy districts in the northern part of the investigated region are characterized by a smaller number of allelic variants and lower heterozygosity, compared to samples from the Kamchatka River basin. A fit to the Hardy-Weinberg distribution was found at most of the loci that were studied in all samples. The average differentiation between populations (st) over the eight loci was 2.93%, which corresponds to the statistical significance level. The most highly polymorphic loci proved to be the least differentiating between the analyzed samples.     

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.