Phenotypic divergence may facilitate co-occurrence in Acanthopagrus species (Family: Sparidae).

Understanding why closely related species co-occur is one fundamental question in ecology. The seabream genus Acanthopagrus Peters, 1855 (Sparidae) is broadly distributed across the Indo-Pacific, with four species, A. arabicus and A. sheim (yellowfin group), and A. bifasciatus and A. catenula (doublebar group), coexisting in the Arabian/Persian Gulf. To investigate how phenotypic divergence facilitates coexistence, a comparative analysis of these four species was conducted across multiple morphological and life-history traits. Differences in body shape, otolith mass and maximum age separated the two species groups, indicating divergence in morphology, auditory characteristics and life-history strategies along the r-K continuum. Intra-group variation was also significant. Divergent growth trajectories and dentition patterns between A. bifasciatus and A. catenula suggest dietary niche partitioning as a potential driver of speciation, while the differences in the monthly gonadosomatic index patterns between A. arabicus and A. sheim indicate the role of temporal reproductive isolation in their speciation. These findings advance our understanding of ecological and evolutionary divergence within Acanthopagrus, highlighting that phenotypic diversification may emerge at multiple nodes across the genus's phylogeny.