Introductions of distinct stocks of chum salmon, Oncorhynchus keta (Walbaum), into natural populations of the species

Populations of chum salmon, Oncorhynchus keta , are recognizable by the allelic frequencies of allozyme loci. Identification of these was used to assess the return of spawning adults to alien rivers into which they were introduced via hatchery-reared, artificially-fertilized eggs obtained from populations elsewhere in the Soviet Far East. Coefficients of return to spawn in the alien rivers were much lower than returns for the native fish, and in succeeding generations the alien fish disappeared from the spawning runs. It is concluded that transplanting salmonid eggs between populations is ineffective as a means of establishing new stock in territory already occupied by another stock, and the practice is deplored on grounds of conserving unique gene pools within species.     

Relation between size-at-maturity and survival of progeny in chum salmon, Oncorhynchus keta (Walbaum)

Data on age- and size-at-maturity, growth, and abundance of chum salmon were collected from 1959 to 1977 at Olsen Creek in Prince William Sound, Alaska. Age composition of spawners (3 to 6-year-olds) varied from year to year: 4-year-old fish were the dominant age group in most (16 out of 19) years and 6-year-old fish usually represented less than 1 % of the returns. Mean size of older spawners was significantly larger than that of younger spawners. Size-at-maturity was similar among fish from different broods maturing at different ages in the same year. Size-at-maturity and survival of progeny were significantly related. The larger the mean size of spawners, the higher the survival rate to adulthood of their progeny. Possible reasons for this relationship are discussed.     

Effect of hypo-osmotic environmental changes on the expression of gonadotropin-releasing hormone,its receptor,and gonadotropin hormone subunit mRNA in adult chum salmon (Oncorhynchus keta)

Migrating fish such as salmonids are affected by external environmental factors and salinity changes are particularly important, influencing spawning migration. The aim of this study was to test whether changes in salinity would affect the expression of the hypothalamic-pituitary-gonadal (HPG) axis hormones (gonadotropin-releasing hormones (GnRHs) [salmon GnRH and chicken GnRH-II], GnRH receptors [GnRHR1 and GnRHR5], and mRNA of the gonadotropin hormone [GTH] subunits [GTHα, follicle stimulating hormone β, and luteinizing hormone β]) in chum salmon (Oncorhynchus keta). Fish were progressively transferred from seawater (SW) through 50% SW to freshwater (FW), and the relationship between the osmoregulatory hormone prolactin (PRL) and sexual maturation was determined. The expression and activity of HPG hormones and their receptors, and levels of estradiol-17β and PRL increased after fish were transferred to FW, demonstrating that changes in salinity stimulate the HPG axis and PRL production in migrating chum salmon. These findings reveal details about the role of the endocrine system in maintaining homeostasis and stimulating sexual maturation and reproduction in response to salinity changes in this species.     

Energy expenditures during spawning by chum salmon Oncorhynchus keta (Walbaum) in British Columbia

Physiological telemetry and proximate tissue analyses were used to assess energy expended by chum salmon Oncorhynchus keta on various behaviours during spawning in Kanaka Creek, British Columbia, Canada, and results were compared with published data on Fraser River sockeye salmon Oncorhynchus nerka , the only other species for which both types of measurements have been taken. Chum salmon arrived at the spawning grounds with body energy densities of 4·84 MJ kg⁻¹ in males and 4·62 MJ kg⁻¹ in females, lower than most sockeye salmon populations, and died with energy densities of c . 4 MJ kg⁻¹, similar to that observed in sockeye salmon and other salmonids. Moisture levels generally increased in body tissues over the spawning life, particularly in female gonads, and lipid levels decreased. Declines in protein observed over the spawning life of other Pacific salmon Oncorhynchus sp. were less evident in Kanaka Creek chum salmon. Holding behaviour constituted the dominant component of the activity schedule and energy budget of both sexes. After holding, the most expensive behaviours were nest digging in females and aggressive displays in males. Dominant males expended the most energy on behaviours each day, as indexed by oxygen consumption (3600 mgO₂ kg⁻¹), while satellite males expended nearly as much (3504 mgO₂ kg⁻¹) but females expended considerably less (2327 mgO₂ kg⁻¹). Kanaka chum salmon engaged more frequently in energetically expensive reproductive behaviours than Stuart River sockeye salmon.     

Microsatellite variability and differentiation of hatchery stocks of chum salmon Oncorhynchus keta Walbaum in Sakhalin

Variability at eight microsatellite loci was examined in five populations of chum salmon Oncorhynchus keta Walbaum from Sakhalin hatcheries. The population of Kalinino hatchery had the lowest heterozygosity and the lowest average number of alleles per locus. The populations examined exhibited significant differentiation, θ_ST = 0.026 on average per locus. The maximum genetic differences were found between the populations of the Kalinino and the Ado-Tymovo hatcheries; the latter differs from the remaining populations also by the highest number and high frequencies of specific alleles. The genetic features of the Taranai hatchery population, observed at microsatellite loci, reflect its “mixed” origin.     

Microsatellite variability and differentiation of hatchery stocks of chum salmon Oncorhynchus keta Walbaum in Sakhalin

Variability at eight microsatellite loci was examined in five populations of chum salmon Oncorhynchus keta Walbaum from Sakhalin hatcheries. The population of Kalinino hatchery had the lowest heterozygosity and the lowest average number of alleles per locus. The populations examined exhibited significant differentiation, theta ST = 0.026 on average per locus. The maximum genetic differences were found between the populations of the Kalinino and the Ado-Tymovo hatcheries; the latter differs from the remaining populations also by the highest number and high frequencies of specific alleles. The genetic features of the Taranai hatchery population, observed at microsatellite loci, reflect its "mixed" origin.     

Mitochondrial DNA variation and genetic population structure of chum salmon Oncorhynchus keta around the Pacific Rim

A survey of mtDNA variation among populations of chum salmon Oncorhynchus keta around the Pacific Rim revealed four large population groups: Rim of the Sea of Japan, the Rim of the Okhotsk Sea and West Bering Sea, North‐west Alaska and Gulf of Alaska. The observed population structure appears to reflect isolation by distance with limited gene flow between regions and larger amounts of gene flow between populations within these four regions.     

Congruent population structure across paralogous and nonparalogous loci in Salish Sea chum salmon (Oncorhynchus keta)

Whole‐genome duplications are major evolutionary events with a lasting impact on genome structure. Duplication events complicate genetic analyses as paralogous sequences are difficult to distinguish; consequently, paralogs are often excluded from studies. The effects of an ancient whole‐genome duplication (approximately 88 MYA) are still evident in salmonids through the persistence of numerous paralogous gene sequences and partial tetrasomic inheritance. We use restriction site‐associated DNA sequencing on 10 collections of chum salmon from the Salish Sea in the USA and Canada to investigate genetic diversity and population structure in both tetrasomic and rediploidized regions of the genome. We use a pedigree and high‐density linkage map to identify paralogous loci and to investigate genetic variation across the genome. By applying multivariate statistical methods, we show that it is possible to characterize paralogous loci and that they display similar patterns of population structure as the diploidized portion of the genome. We find genetic associations with the adaptively important trait of run‐timing in both sets of loci. By including paralogous loci in genome scans, we can observe evolutionary signals in genomic regions that have routinely been excluded from population genetic studies in other polyploid‐derived species.     

Crystal structure and nucleotide sequence of an anionic trypsin from chum salmon (Oncorhynchus keta) in comparison with Atlantic salmon (Salmo salar) and bovine trypsin

The nucleotide sequence and crystal structure of chum salmon trypsin (CST) are now reported. The cDNA isolated from the pyloric caeca of chum salmon encodes 222 amino acid residues, the same number of residues as the anionic Atlantic salmon trypsin (AST), but one residue less than bovine beta-trypsin (BT). The net charge on CST determined from the sum of all charged amino acid side-chains is -3. There are 79 sequence differences between CST and BT, but only seven sequence differences between CST and AST. Anionic CST isolated from pyloric caeca has also been purified and crystallized; the structure of the CST-benzamidine complex has been determined to 1.8A resolution. The overall tertiary structure of CST is similar to that of AST and BT, but some differences are observed among the three trypsins. The most striking difference is at the C terminus of CST, where the expected last two residues are absent. The absence of these residues likely increases the flexibility of CST by the loss of important interactions between the N and C-terminal domains. Similarly, the lack of Tyr151 in CST (when compared with BT) allows more space for Gln192 in the active site thereby increasing substrate accessibility to the binding pocket. Lys152 in CST also adopts the important role of stabilizing the loop from residue 142 to 153. These observations on CST provide a complementary view of a second cold-adapted trypsin, which in comparison with the structures of AST and BT, suggest a structural basis for differences in enzymatic activity between enzymes from cold-adapted species and mammals.     

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.     

Linkage mapping with paralogs exposes regions of residual tetrasomic inheritance in chum salmon (Oncorhynchus keta)

Gene sequence similarity due to shared ancestry after a duplication event, that is paralogy, complicates the assessment of genetic variation, as sequences originating from paralogs can be difficult to distinguish. These confounded sequences are often removed prior to further analyses, leaving the underlying loci uncharacterized. Salmonids have only partially rediploidized subsequent to a whole‐genome duplication; residual tetrasomic inheritance has been observed in males. We present a maximum‐likelihood‐based method to resolve confounded paralogous loci by observing the segregation of alleles in gynogenetic haploid offspring and demonstrate its effectiveness by constructing two linkage maps for chum salmon (Oncorhynchus keta), with and without these newly resolved loci. We find that the resolved paralogous loci are not randomly distributed across the genome. A majority are clustered in expanded subtelomeric regions of 14 linkage groups, suggesting a significant fraction of the chum salmon genome may be missed by the exclusion of paralogous loci. Transposable elements have been proposed as drivers of genome evolution and, in salmonids, may have an important role in the rediploidization process by driving differentiation between homeologous chromosomes. Consistent with that hypothesis, we find a reduced fraction of transposable element annotations among paralogous loci, and these loci predominately occur in the genomic regions that lag in the rediploidization process.     

Genetic variability and differentiation of populations of chum salmon Oncorhynchus keta (Walbaum) from the southern Russian Far East

Allozyme variation of populations of chum salmon Oncorhynchus keta from southern Russian Far East was examined. Of 55 loci screened, 31 were polymorphic. Within-population variation accounted for most of the allele diversity; FST averaged over loci was 0.052. Linkage disequilibrium was found in less than 5% of locus pairs in the chum population examined. Analysis of within- and among-population variance components of linkage disequilibrium using D-statistics (Ohta, 1982) showed that most genetic variation was distributed among populations.     

Genetic stock structure of odd-year pink salmon, Oncorhynchus gorbuscha (Walbaum), from Washington and British Columbia and potential mixed-stock fisheries applications

We used electrophoresis to determine the number and characteristics of genetically distinct stocks of odd-year pink salmon in Washington and southern British Columbia. We analysed 5128 fish from 52 collections (taken in 1985, 1987 and 1989). We observed genetic variation at 53 enzyme-coding loci, 19 of which were polymorphic at the P_o-95 level in at least one stock. Genotypic proportions conformed to Hardy-Weinberg expectations in nearly all cases. The genetic profiles of individual populations were generally stable over the three cycle years studied. Significant differences in allele frequencies at sAAT-3* , PEP-LT* and PGDH* for several stocks were, however, noted between this study and previously reported data for pink salmon. We used G-tests and cluster analysis of genetic distances to evaluate genetic interrelationships among collections and to define genetically distinct stocks. Differentiation among stocks exhibited a clear geographic pattern with three major clusters of stocks recognizable: (1) Hood Canal and Washington Strait of Juan de Fuca stocks, (2) Puget Sound, Fraser River, and southern Canada South Coast stocks, and (3) northern Canada South Coast stocks and Canada North Coast stocks. Computer simulations using 14 and 28 loci, and sample sizes of 15C600, demonstrated that accurate estimates of stock-group composition could be obtained for pink salmon fisheries having a considerable range of stock compositions. The simulations revealed that approximately 50% fewer fish were required to obtain a given level of precision of stock group composition estimates with 28 loci as with the set of 14 loci used in previous investigations.     

Mitochondrial DNA variation in populations of the chum salmon Oncorhynchus keta (Walbaum) from rivers of the Prymorye and Sakhalin

Mitochondrial DNA (mtDNA) variation was studied using restriction fragment length polymorphism (RFLP) in chum salmon populations from three rivers in southern Primorye and one river in Sakhalin Island. Significant differences were detected between the samples from Primorye and Sakhalin Island. No differences were found between the samples from the rivers of Primorye, which can be explained by a high rate of gene flow due to transplantation of spawn from one river to another. The effect of fish breeding on the chum salmon populations correlated with the indices of haplotype and nucleotide diversity (h and pi, respectively). The lowest diversity was found in the completely artificial population from the Ryazanovka River; the highest, in natural populations from the Narva and Naiba rivers. Frequencies of haplotypes in consecutive generations were significantly different, which confirms the effects of genetic drift on the small-size chum salmon populations of Primorye.     

The influence of food distribution upon the development of aggressive and competitive behaviour in juvenile chum salmon, Oncorhynchus keta

Groups of juvenile chum salmon were reared on food that was either dispersed throughout, or localized in one area of, the rearing tank. Groups receiving localized food displayed more aggression than those receiving dispersed food. This led to differences in growth, with fish reared on localized food having greater individual growth variability, i.e. growth depensation. However, after several months of rearing in these different feeding/social environments, fish reared on dispersed food were just as aggressive when first exposed to localized food as were fish reared on localized food. Furthermore, in competitive contests between fish of the two rearing histories, those reared on dispersed food were just as likely to become dominant as those reared on localized food. These results suggest that the behavioural development of aggressiveness is not amenable to alteration by manipulation of food distribution.     

Embryonic origin and development of the corpuscles of Stannius in chum salmon (Oncorhynchus keta)

Summary An immunocytochemical technique was used to follow the embryological origin and development of the corpuscles of Stannius (CS) in the chum salmon, Oncorhynchus keta. Stanniocalcin immunoreactive (ir-) cells can be observed as early as 13 days before hatching. The ir-CS cells appear in clusters of variable size in close association with nephric ducts. In addition, individual ir-cells also occur at this stage amoung epithelial cells of the nephric ducts. these individual cells may give rise to clusters which subsequently increase in size, the largest reaching 100 m in diameter by the time of hatching. During this period, dispersed CS cells become evident and develop into secondary clusters in the vicinity of the primary clusters. These clusters appear to fuse to form larger clusters with a lobular structure. Transfer of the larvae (20 days after hatching) from fresh water to 50% seawater, accelerates the development of the CS tissue, suggesting an important role of the CS in seawater adaptation.     

Critical swimming velocities of juvenile sockeye salmon and kokanee, the anadromous and non-anadromous forms of Oncorhynchus nerka (Walbaum)

In streams tributary to the North Pacific, anadromous sockeye salmon and non-anadromous kokanee, Oncorhynchus nerka (Walbaum), occasionally spawn sympatrically and male kokanee may act as 'sneaks’to spawn with the larger female sockeye. Despite this interbreeding, sockeye and kokanee exhibit persistent biochemical genetic differences at several enzyme loci. Genetic differences between forms may be maintained by selection against‘hybrids’due to the different life histories of sockeye and kokanee; sockeye make extensive smolt, oceanic, and spawning migrations while kokanee reside permanently in fresh water. We tested the sustained swimming abilities of juvenile sockeye, kokanee, and sockeye (female) × kokanee (male) hybrids to see if hybrids were inferior to sockeye in a trait that is probably under stronger selection in an anadromous life history. Sockeye had significantly greater mean critical swimming velocities (U_crit) than kokanee of the same size raised under identical conditions (8.3 v. 7.3 body lengths s^?1 respectively). When tested 1 month later the mean U_crit of sockeye was only marginally greater than that for sockeye × kokanee hybrids (both c. 6.6 body lengths s^?1). Sockeye swimming performance was also less variable than that of either kokanee or hybrids. Sockeye tended to have slimmer bodies and longer caudal regions than kokanee or sockeye × kokanee hybrids of the same size. Sockeye also had significantly more vertebrae than kokanee and hybrids, while hybrids had more vertebrae than kokanee. These morphological differences may have contributed to the differences in swimming performance. We concluded: (i) that juvenile sockeye and kokanee have diverged with respect to sustained swimming performance and that reduced performance by kokanee may be due to relaxed selection for sustained swimming performance associated with their non-anadromous life history, (ii) that sockeye × kokanee hybrids appear to have modestly lower swimming capabilities than pure sockeye, and (iii) if the variability in swimming performance is associated with differences in survival in nature, then such differences may promote divergence between sympatric sockeye and kokanee.     

Genetic diversity and differentiation of masu salmon (Oncorhynchus masou masou) between and within cultured populations inferred from microsatellite DNA analysis

Masu salmon,Oncorhynchus masou masou,is one of the most valuable fishery species that has been introduced to China,though to date no studies on the genetic diversity and genetic relationship among hatchery populations has been performed with molecular markers.We undertook such a study and sampled 120 individuals from three hatchery stocks and analyzed 20 microsatellite loci.All loci were polymorphic and a total of 91 alleles were detected.A relatively low level of genetic diversity was revealed with effective number of allele of 3.1094,3.3299 and 3.1894 and expected heterozygosity of 0.6600,0.6648 and 0.6638 in the three stocks,respectively.Deviations from Hardy-Weinberg equilibrium were found due to heterozygote deficit.Accordingly,evidence of genetic bottlenecks were found in the three stocks.An individual assignment test demonstrated that 85% of individuals were correctly assigned into their original stocks.Pairwise Fst revealed that significant differentiation occurred between these three stocks.The results of the study indicated that disequilibrium of genetic structure and differentiation has occurred in all three stocks.This information collectively provides a basis for measures to avoid of loss of genetic diversity and introgression in Chinese aquaculture.     

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.