Some biological features of pink salmon Oncorhynchus gorbuscha (Walbaum, 1792) spawners in odd-numbered years in the Kola River

The results of a comprehensive study of the pink salmon population Oncorhynchus gorbuscha (Walbaum, 1792) in the Kola River (Murmansk region) in the summer of 2023 are presented. The material comprised 19 odd-year spawners, for which size-weight parameters, sex structure, allometric growth patterns, and parasite fauna composition were analyzed. Body length ranged from 36.0 to 53.6 cm (mean 46.7 cm), and weight ranged from 0.8 to 1.9 kg (mean 1.3 kg). The sex structure was characterized by a significant predominance of females (68%), which distinguishes this population from the adjacent Tuloma River, where the sex ratio is close to equilibrium (1 : 1). Using Student's t-test (tkp = 2.11, df = 17), no statistically significant differences in body size between males and females were found, indicating the absence of pronounced sexual dimorphism in the studied sample – a feature uncharacteristic of many other rivers in the region. The constructed power equations describing the relationship between weight and length for males (y = 0.23x2.22) and females (y = 0.24x2.25) demonstrate similar allometric growth patterns in both sexes. Parasitological examination revealed 8 helminth species of predominantly marine origin (Lecithaster salmonis, Hysterothylacium aduncum, Scolex polymorphus, Derogenes varicus, Eubothrium crassum, and others), indicating infestation during the marine feeding period. The high occurrence of the trematode Podocotyle atomon (26-33%) deserves special attention, confirming the significant role of benthophagy in the diet of Barents Sea pink salmon – a trait distinguishing it from Pacific populations with predominantly pelagic feeding. The obtained results highlight the local adaptive features of the Kola River population, shaped by the specific feeding conditions in the Barents Sea, the hydrological regime of the river system, and the characteristics of spawning migration.