Spatial variability of growth improvement based on river use in Japanese seabass

Japanese seabass (Lateolabrax japonicus) exhibits partial migration, wherein some individuals seasonally inhabit estuaries and freshwater environments while others complete their life cycle in marine environments. We hypothesized that seabass exhibit different growth patterns in marine and riverine environments at different geographic locations. To elucidate the commonalities and differences in growth, river use, and their interrelationships across different locations, we investigated seabass growth across marine and riverine environments at three distinct locations in Japan: northern (Miyagi), central (Kyoto), and southern (Oita). Annual growth from ages 0–5 was compared by measuring otolith increment widths, and river use histories were reconstructed from the otolith Sr/Ca ratios. The results indicated that females often rely more heavily on riverine environments than males. Linear mixed models were used to assess the effects of river use and geographic location on the annual growth rates. River use had a positive or neutral effect on growth and riverine growth improvements were lowest in the northern location among our study locations. Additionally, growth rates at ages 0–1 were also lowest in the northern location among the three locations. In contrast, the standard length at older ages was longer at more northern locations. These findings suggest that lower temperatures contribute to slower growth at younger ages, whereas higher temperatures may limit body size at older ages. The distinct characteristics of early growth, growth improvement in rivers, and body size at older ages observed at each geographical location may be responsible for the different growth strategies.