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 of Striostrea prismatica: phase I from mixotrofic to early umbonated veliger larva and phase II until eyespot larvae. The monoalgal diets in phase I were Tisochrysis lutea, Pavlova lutheri and Nannochloropsis sp. In phase II, Tetraselmis suecica, T. chuii, Chaetoceros gracilis and Ch. muelleri were incorporated. The bialgal diets (combination of P. lutheri + Ch. gracilis in 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 combination T. lutea + Ch. gracilis, initially using T. lutea for mixotrophic larvae (6 days Post Fertilization-PF), then incorporating Ch. gracilis in 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.