Chum Salmon Oncorhynchus Keta Walbaum Research Articles

Comparative characteristics of the trace elemental composition of chum salmon Oncorhynchus keta Walbaum, 1792 from the Sea of Japan and the Sea of Okhotsk

Content of trace elements (iron, zinc, copper, nickel, lead, and cadmium) was determined in the most popular species of Pacific salmon on the consumer market – chum salmon Oncorhynchus keta, which is the second largest catch in Russian waters (after pink salmon O. gorbuscha). Metal content in fish organs and tissues (muscle tissue, liver, and gonads) was determined by the atomic absorption method using a Shimadzu AA-6800 spectrophotometer in flame and flameless atomizers from sample extracts; the latter ones were obtained by decomposition of weighed portions of concentrated HNO3 (high purity) in a MARS 6 complex using standard samples with known concentrations. The data was statistically processed in SPSS Statistics 21. Sexually mature individuals of chum salmon (five specimens of males and females on each spot) were sampled in autumn 2018 in storage cages of salmon hatcheries on the Firsovka River (southeastern Sakhalin, Gulf of Patience) and Reidovaya River (Iturup Island, Kuril Islands), as well as in October 2019 in breeder holding cages on the Poima River (southwestern Primorye, the Sea of Japan). Muscle tissue, liver, and gonads were sampled from every individual. The elements determined were clearly divided according to content values into two groups depending on the sampling spot: Cd and Pb prevailed in organs and tissues of chum salmon from the Sakhalin-Kuril Region of the Sea of Okhotsk, whereas Fe, Zn, Cu, and Ni prevailed in the Sea of Japan fish. The reason for heavy metal contrasting distribution in fish organs and tissues is obviously environmental geochemical conditions formed in salmon feeding areas and on migration routes. In the Sea of Japan, practically enclosed, poorly connected with the Pacific Ocean by several shallow straits, the aquatic environment is under significant anthropogenic, technogenic, and terrigenous load (household and industrial drains, surface washing from coastal areas, and combustion of hydrocarbon fuel by ships). In the Sakhalin-Kuril basin, it is affected by natural phenomena: surface and underwater volcanism and post-volcanism of the Kuril Islands, as well as upwellings, which carry from the depths of the Kuril–Kamchatka Trench into the surface layer practically the entire set of chemical elements of the Mendeleev’s periodic table. At the same time, Pb, with its unusually high sorbability, is retained on any suspended particles, both living and non-living, and enters fish organisms with food. The distribution of trace elements over chum salmon organs and tissues differs significantly. Specifically, in fish muscle tissues, the lowest metal content is observed, regardless of the catch spot. The liver is characterized by increased levels of all metals, except for Ni, with the highest Fe, Zn, and Cu content recorded in the Sea of Japan fish liver. The distribution of metals in fish gonads is characterized by its own specificity, with very clear manifestation in the Primorye salmon. Thus, in female gonads, Fe, Zn, and especially Cu predominated: Cu content in female gonads from the Poima River was the same as in liver. Female gonads of the Sea of Japan chum salmon had the highest Ni concentration, although male gonads were characterized by a high, albeit very variable, content of this element as well. As for Pb and Cd, the most toxic elements monitored by sanitary services (for technical reasons, we determined their amount in the Sea of Okhotsk fish only), a well-known pattern was observed in their distribution in organs and tissues: maximum content was found in fish liver. Pb content exceeded the sanitary standard only in some individuals that came to spawn in the Firsovka River in the southeastern Sakhalin. Cd concentration in Sakhalin fish liver was 2.5–4.0 times higher than threshold limit value, and in Kuril fish liver, 2.1–5.0 times higher.

The Olfactory Transcriptome and Progression of Sexual Maturation in Homing Chum Salmon Oncorhynchus keta.

Reproductive homing migration of salmonids requires accurate interaction between the reception of external olfactory cues for navigation to the spawning grounds and the regulation of sexual maturation processes. This study aimed at providing insights into the hypothesized functional link between olfactory sensing of the spawning ground and final sexual maturation. We have therefore assessed the presence and expression levels of olfactory genes by RNA sequencing (RNAseq) of the olfactory rosettes in homing chum salmon Oncorhynchus keta Walbaum from the coastal sea to 75 km upstream the rivers at the pre-spawning ground. The progression of sexual maturation along the brain-pituitary-gonadal axis was assessed through determination of plasma steroid levels by time-resolved fluoroimmunoassays (TR-FIA), pituitary gonadotropin subunit expression and salmon gonadotropin-releasing hormone (sgnrh) expression in the brain by quantitative real-time PCR. RNAseq revealed the expression of 75 known and 27 unknown salmonid olfactory genes of which 13 genes were differentially expressed between fish from the pre-spawning area and from the coastal area, suggesting an important role of these genes in homing. A clear progression towards final maturation was characterised by higher plasma 17α,20β-dihydroxy-4-pregnen-3-one (DHP) levels, increased pituitary luteinizing hormone β subunit (lhβ) expression and sgnrh expression in the post brain, and lower plasma testosterone (T) and 17β-estradiol (E2) levels. Olfactomedins and ependymin are candidates among the differentially expressed genes that may connect olfactory reception to the expression of sgnrh to regulate final maturation.

Patterns of genetic diversity in population complexes of pacific chum salmon Oncorhynchus keta Walbaum, from Asia and America, inferred from allozyme polymorphism data

Based on the data of Russian and foreign researchers, a database, consisting of 100 allozyme-coding loci examined in 288 chum salmon populations from Asia and Northern America, was constructed. Using G-test, genetic heterogeneity of Asian population samples of chum salmon was evaluated. Correlations between the frequencies of major alleles and geographic latitude of the mouths of native rivers were estimated. Using the methods of Nei and Cavalli-Sforza and Edwards, for different local chum salmon stock groups the genetic distances at the number of polymorphic enzyme loci were determined. Analysis of these distances made it possible to evaluate the patterns of genetic diversity in regional population groups from the Russian Far East, Japan, and North America. The proportions of genetic variation at each hierarchical level, identified in accordance with the geographical positions of the populations, were estimated through partitioning of variation in Asian populations into within and between-population components. It was demonstrated that intraspecific genetic structure of chum salmon corresponded geographic subdivision into regional population groups.

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.

Genetic Variation and Differentiation among Populations of Chum Salmon Oncorhynchus ketaWalbaum from Southern Russian Far East

Allozyme variation of populations of chum salmon Oncorhynchus ketafrom southern Russian Far East was examined. Of 55 loci screened, 31 were polymorphic. Within-population variation accounted for most of the allele diversity; F STaveraged 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.