Growth, survival, maturation and proximate composition of dorsal muscle in diploid and triploid male and female masu salmon Oncorhynchus masou masou under communal rearing in seawater

Triploid all-female salmonids are used in aquaculture to mitigate the negative effects of sexual maturation; however, little is known about how triploidy and sex influence aquaculture performance in masu salmon Oncorhynchus masou masou reared in seawater. In this study, 1 + -year-old diploid and triploid males and females produced from the same broodfish were individually identified using PIT tags and communally reared in a 30 m 3 seawater tank. Growth, gonadal development, and dorsal muscle proximate composition were compared among groups. From January to September 2023, total length and body weight were measured at four time points, and gonadosomatic index (GSI) and muscle composition were analyzed in May and September. Diploid females exhibited higher growth until May, whereas triploid females showed significantly greater weight gain than other groups by September. The GSI of triploid females remained near zero throughout the experiment, while that of diploid females increased to 28.2 ± 5.1% in September. Although no differences in muscle composition were observed in May, triploid females exhibited significantly higher crude lipid content (16.6 ± 1.9%) than diploid females (10.2 ± 2.4%) in September. These results indicate that, under the present rearing conditions, triploid females may maintain superior flesh quality during the maturation period.