Comparative characteristics of the trace elemental composition of chum salmon Oncorhynchus keta Walbaum, 1792 from the Sea of Japan and the Sea of Okhotsk
Authors: Khristoforova N. K. , Litvinenko A. V. , Tsygankov V. Yu. , Kovalchuk M. V. 
Published: November 2021

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.