Ecomorphology of three closely related Sebastes rockfishes with sympatric occurrence in Seto Inland Sea, Japan

Ecological diversification of Sebastes rockfishes has been mainly driven by depth and resource availability. Both ecological parameters exert selective pressures in colouration, communication systems, body, otolith shape, and prey–predation interactions. Accordingly, we hypothesized that ecomorphological divergences found in these components can reflect reduced interspecific competition among three rockfishes from the same species complex with sympatric occurrence in Seto Inland Sea (Japan). The narrower body shape and golden-brown colouration in Sebastes cheni suggest a more pelagic lifestyle than the other two species. Larger eye and otolith relative sizes, deeper body shape and red colouration suggest a deeper distribution for Sebastes inermis, in concordance with longer pectoral fins and dorsal spines to deal with increased foraging difficulty and predation risk because of its colouration. Meanwhile, smaller upper jaws, higher number of gill rakers, and black colouration of Sebastes ventricosus indicate a shallower distribution than S. inermis and preference for planktonic preys. Differences in colouration, eye size, and otolith descriptors support species-specific communication systems that are crucial to maintaining reproductive isolation. Therefore, the morphological divergences among these rockfishes reflect specific ecological divergences that allow their coexistence in sympatry and can ease their morphological identification.