Sexual dimorphism in four species of rockfish genusSebastes (Scorpaenidae)

Synopsis Sexual dimorphisms, and factors influencing the evolution of these differences, have been investigated for four species of rockfish:Sebastes melanops, S. flavidus, S. mystinus, andS. serranoides. These four species, which have similar ecology, tend to aggregate by species with males and females staying together throughout the year. In all four species adult females reach larger sizes than males, which probably relates to their role in reproduction. The number of eggs produced increases with size, so that natural selection has favored larger females. It appears males were subjected to different selective pressures than females. It was more advantageous for males to mature quickly, to become reproductive, than to expend energy on growth. Other sexually dimorphic features include larger eyes in males of all four species and longer pectoral fin rays in males of the three piscivorous species:S. melanops, S. flavidus, andS. serranoides. The larger pectoral fins may permit smaller males to coexist with females by increasing acceleration and, together with the proportionately larger eye, enable the male to compete successfully with the female to capture elusive prey (the latter not necessarily useful for the planktivoreS. mystinus). Since the size of the eye is equivalent in both sexes of the same age, visual perception should be comparable for both sexes.