Larval rearing and weaning of Seabass, Lates calcarifer (Block), on experimental compounded diets.

Larval rearing trials of seabass larvae, either imported from Singapore or obtained from the captive broodstock of IFREMER/C.O.P. at Tahiti, were carried out since 1987, by testing different technologies originally used in South East Asia (green-water culture, sequential water changes) or developed by IFREMER for other species (clear water system, preys enrichment, continuous water renewal). The preliminary results reveal a high variation of survival and growth rates after the first month, which are not clearly related to one of the closen rearing technic. Best results are obtained at a starting density of 30 larvae/liter in 450 liter cylindro-conical tanks whith a survival rate superior to 50-60 %, for a final mean weight of 20 mg on day 25. In other trials, strong mortalities are observed from day 12 to 14 with symptoms of depigmentation, over-inflation of the swimbladder and abnormal swimming behaviour followed by death. Histological observations studies reveal vacuols appearing in retinal, CNS and liver a few days before the first symptoms. Pathological researches are now under way to reduce these mortalities and explain these phenomenons. No clear relation with nutritional deficiency is demonstrated. The weaning of seabass larvae on artificial pellet is feasible as early as the 25th day when the mean weight of fry ranges from 20 to 40 mg with alternative food sequences of live to frozen Artemia and dry pellet containing a high protein (56 %) and lipid (16 %) level. A grading sequence has been defined, which allows to reduce the cannibalism observed as soon as live preys are replaced by artificial diet. Survival rates (50 %) and growth results (mean weight between I and 2 g on day 80) are similar to those obtained by other research teams in Singapore and Australia, and confirm the good ability of seabass fry to accept dry pelleted feeds. Preliminary experiments to replace live prey by artificial microparticulate diet (MD) as soon as the 15th day (mean weight inferior to 15 mg) have been conducted with encouraging results.