Spawning, larval culture, settlement and juvenile production of the west Indian Sea egg, Tripneustes ventricosus (Lamarck, 1816), under hatchery conditions

Tripneustes ventricosus is a commercially important species of sea urchin native of the tropical Atlantic Ocean. With the purpose of providing a scientific basis for the development of its production by aquaculture, several experiments were performed under hatchery conditions, including spawning induction, larval culture, settlement and juvenile culture. The efficiency of different spawning stimuli was assessed, including the use of UV-irradiated seawater; thermal and electric shocks, and injections of potassium chloride (KCl) and acetylcholine (ACh). Growth and survival of larvae maintained at different culture conditions were compared, including culture densities (2, 6 and 12 zygotes mL⁻¹; 0.5, 1 and 2 larvae mL⁻¹), culture systems (9 L aquaria, 75 L and 500 L tanks), water renewal rates (total and partial), feed amount (15 and 30 cells μL⁻¹ d⁻¹), feeding regime (constant or increasing) and type of diet (Isochrysis galbana, and a mixture of I. galbana and Chaetoceros calcitrans). Different stimuli to induce the larval settlement were tested, including low temperature, KCl, l-glutamine and γ-aminobutyric acid (GABA), as well as different substrates (artificial and benthonic microalgae biofilms). Finally, the growth and survival of juveniles were assessed under indoor conditions. The highest percentage of spawning individuals and the shorter response times were obtained using ACh. The average fecundity was 1.5 × 10⁶ oocytes female⁻¹. This variable exhibited a positive correlation with the female body size. One of the most relevant results of the present study was the completion of the embryo and larval developmental stages of T. ventricosus. Higher levels of larval either survival or growth were found in the tanks with the highest volume (500 L), maintaining conditions of low culture densities and complete water renewal and a constant supply of microalgae during all the larval development stage (15 cells of I. galbana and C. calcitrans μL⁻¹ day⁻¹). The larval settlement was obtained using low temperatures in all the tested substrates, except the substrate with artificial biofilm containing Sargassum and Thalassia. After 9 months of culture in laboratory conditions, juveniles of 44-mm length were obtained, using a regime of complete water renewal, and feeding the larvae with artificial biofilm, benthic microalgae and macroalgae. Although the present study made possible to identify appropriate culture conditions for obtaining hatchery-reared juveniles of white sea urchin, the low survival rates observed during the larval culture and the settlement stage must be improved with further research on the feeding requirements and the optimal water quality conditions for this species.