MALE MATING EFFORT IN THE VIVIPAROUS SCORPIONFISH, SEBASTISCUS-MARMORATUS

Males of some internally fertilizing fishes devote reproductive effort s not only to mating activities but also to sperm production. Male rep roductive efforts of the viviparous scorpionfish, Sebastiscus marmorat us, an ambush predator usually remaining on the substrate, were studie d at a rocky coast in southern Japan. During the mating season in earl y winter, males actively visited and courted several females, and inte racted aggressively with other males. Females remained stationary. Sea sonal changes in somatic and gonad weights suggested that males devote reproductive efforts to such mating activities, rather than to sperm production. Because females almost always ignored frequent courtships from several males, resulting in infrequent copulations, and would rar ely copulate with multiple males, sperm competition is not likely to b e intensive. Accordingly, males may increase mating efforts while reta ining small testis size (max. GSI=0.4%), smaller than that in many ext ernally fertilizing fishes. The reproductive effort of this species is compared with that of other viviparous fishes.