Microalgal diet evaluation in the larval development and substrate selection for settlement in the rock oysterStriostrea prismatica (Gray, 1825)

Abstract

Monoalgal and bialgal diet were tried in 2 stages of larval development ofStriostrea prismatica: phase I from mixotrofic to early umbonated veliger larva and phase II until eyespot larvae. The monoalgal diets in phase I wereTisochrysis lutea,Pavlova lutheriandNannochloropsissp. In phase II,Tetraselmis suecica,T. chuii,Chaetoceros gracilisandCh. muelleriwere incorporated. The bialgal diets (combination ofP. lutheri + Ch. gracilisin proportions 1:3, 1:1 and 3:1) were chosen according to the results of the monoalgal trials and were evaluated against the classic diet = control (T. lutea + Ch. gracilis). The microalgae size and their fatty acid composition were determined. We recommend the combinationT. lutea + Ch. gracilis, initially usingT. luteafor mixotrophic larvae (6 days Post Fertilization-PF), then incorporatingCh. gracilisin a ratio of 1:1 until completing phase I (8-10 PF). In phase II, the ratio should change to 1:3 until larvae with eyespot are obtained (18-20 PF). Suggestions were based on the higher demand for DHA in initial larvae and the need for EPA from the early umbonated phase. Finally, as a third experiment, microsubstrates (pieces of shells, sandpaper, polycarbonate and ground rubber) were evaluated to promote the settlement of pediveliger larvae. A settlement of 20% was obtained in pieces of shells of the same species. We consider that the settlement technology has not been optimized; therefore, evaluations directed at the behaviour of the species are recommended.