Evaluation of partial substitution of live algae with dried Tetraselmis for larval rearing of black-lip pearl oyster, Pinctada margaritifera (L.)

Experiments were conducted with larvae of the black-lip pearl oyster, Pinctada margaritifera fed on a regime of living algae (an equal mixture of Tahitian Isochrysis aff. galbana and Pavlova salina) either partially or completely substituted with heterotrophically grown spray-dried algae (Tetraselmis suecica). Two experiments were conducted; in the first, 1-day old larvae were cultured for 13 days and, in the second, 13 days old larvae were cultured for 7 days. In both experiments larvae were fed the following proportions of live algae (LA) and dried Tetraselmis (DT); (1) 100% LA, (2) 75% LA + 25% DT, (3) 50% LA + 50% DT, (4) 25% LA + 75% DT; and (5) 100% DT. The optimal diets for maximum larval growth were 100% LA and 75% LA + 25% DT resulting in larvae with a mean shell length (SL) of 132 +/- 3.8 and 131 +/- 2.7 mum, respectively, at day 13. This showed that 25% substitution of live micro-algae with DT is possible without affecting growth of P. margaritifera larvae of less than 150 mum SL. There was no significant difference in survival of P. margaritifera larvae fed 100% LA, 75% LA + 25% DT and 50% LA + 50% DT over a period of 13 days. Highest survival (43.7%) occurred in larvae fed 100% DT while lowest (approximately 18%) occurred in controls (50% live micro-algae and unfed) during the first experiment. The result of the second experiment indicated that with increasing size, larvae are capable of accepting a higher proportion of dried Tetraselmis in their diet. There were no significant differences in larval growth or survival, between treatments where LA was partially and completely substituted with DT.