REPRODUCTION, EMBRYONIC ENERGETICS, AND THE MATERNAL-FETAL RELATIONSHIP IN THE VIVIPAROUS GENUS SEBASTES (PISCES: SCORPAENIDAE).

Reproduction in the scorpaenid genus Sebastes has been characterized as primitive ovoviviparity. In the black rockfish, S. melanops, egg size is small (0.8 mm), but the gestation period is 37 days and larvae at birth are well developed, with a remnant of yolk and the ability to initiate feeding. To test the hypothesis that this species is viviparous with additional maternal nutrition, we studied embryonic energetics and morphology. Catabolism during development utilized 64% of the yolk energy, resulting in a maximum yolk utilization efficiency of 36%, similar to oviparous fishes. Calorimetry, however, demonstrates that 81% of the initial yolk energy is present at birth. Thus approximately 70% of the catabolic energy is contributed by the maternal system during gestation. Microscopic analysis of embryonic epidermis suggests no specializations for nutrient uptake. Histological observations, however, reveal that the hindgut is functional approximately 22-25 days after fertilization. Thus, we suggest that nutrition occurs through consumption and assimilation of ovarian fluid. Reproductive modes in the Scorpaenidae have apparently evolved from simple oviparity in seven of eight subfamilies, to lecithotrophic viviparity in more primitive members of the subfamily Sebastinae, through matrotrophic viviparity in Sebastes. This pattern involved progressively longer retention of embryos until after organogenesis and functional differentiation of the gut, facilitating this rather primitive form of embryonic nutrition among matrotrophic viviparous species.