Male mating effort in the viviparous scorpionfish,Sebastiscus marmoratus

Males of some internally fertilizing fishes devote reproductive efforts not only to mating activities but also to sperm production. Male reproductive efforts of the viviparous scorpionfish,Sebastiscus marmoratus, an ambush predator usually remaining on the substrate, were studied at a rocky coast in southern Japan. During the mating season in early winter, males actively visited and courted several females, and interacted aggressively with other males. Females remained stationary. Seasonal 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 rarely copulate with multiple males, sperm competition is not likely to be intensive. Accordingly, males may increase mating efforts while retaining small testis size (max. GSI=0.4%), smaller than that in many externally fertilizing fishes. The reproductive effort of this species is compared with that of other viviparous fishes.