AN EVALUATION OF THE PERFORMANCE OF MANILA CLAM SPAT (TAPES-PHILIPPINARUM) FED ON DIFFERENT RATIONS OF SPRAY-DRIED ALGAE (TETRASELMIS-SUECICA)

This paper evaluates the performance of Manila clam spat (Tapes philippinarum) fed on spray-dried algae (Tetraselmis suecica) either as a supplement to live algae (Chaetoceros calcitrans) or as 100% rations. The work was in two phases. Initially, spat from the same cohort were provided with mixtures of dried and live algae diets, ranging from 100% dried to 100% live algae. Best performances were obtained from 80%/20% and 60%/40% mixtures of live/dried algae, respectively. The second phase compared the performance of spat, from the same cohort, fed on the best two mixtures, against a control of 100% live algae. The real contribution of the dried algae was evaluated simultaneously by comparing growth at four dilutions (80, 60, 40 and 20%) of live rations to the 100% control. Dried algae food supplements of 20 and 40% contributed to growth of Manila clam spat and compared favourably with 100% live algal rations, while larger proportions of dried food resulted in decreased growth. Depending on the unit production cost of live algae in any particular mollusc nursery system, dried algae may provide a cost-effective food supplement and an insurance against total or partial collapse of a live algal culture system during periods of heavy animal stock density.