Variation patterns and ecological drivers of morphology in different body regions of fishes from the Northwest Pacific Ocean

Abstract Variation in fish body morphology represents an important aspect of phenotypic diversity and plays a fundamental role in understanding fish evolution and ecology. The complex oceanographic conditions of the Northwest Pacific Ocean create diverse selective pressures, making it an ideal system for studying how environmental variability shapes fish body morphology. While previous macroecological studies have linked fish morphology to environmental factors, the driving factors of regional morphological differences were seldom explored. In this study, morphological variations among different body regions (entire body, head, torso and tail) of 22 fish species from the Northwest Pacific Ocean were analysed to explore the phylogenetic and ecological drivers of these variations with geometric morphometrics (GMs) in a phylogenetic framework. The results showed significant morphological differences among orders and species. Entire body, head, torso and tail exhibited low to moderate phylogenetic signals. Ecological factors, including latitudinal range, temperature preference, fecundity and trophic level, significantly shaped morphological variations, thus emphasizing the complex interplay between ecological and evolutionary pressures. We confirmed that different body regions are subject to distinct selective pressures, reflecting the combined influence of genetic and environmental factors. Overall, this study highlights the combined influence of phylogenetic history and ecological pressures in shaping fish morphology. These findings improve understanding of fish evolutionary biology and provide a foundation for conservation and species management in the Northwest Pacific.