Use of spray-dried Schizochytrium sp. as a partial algal replacement for juvenile bivalves

The use of spray-dried heterotrophically grown microalgae as an aquaculture feed has been previously evaluated. However, these strains were selected more for their heterotrophic culture potential than for their nutritional profile, particularly their n = 3 and n = 6 HUFA. This paper evaluates the performance of Manila clam spat (Tapes semidecussata) and Pacific oyster spat (Crassostrea gigas) fed on two different ratios of a spray-dried preparation of heterotrophically grown Schizochytrium sp., an algae of very high HUFA concentration. The work consisted of two separate experiments conducted in duplicate. Both experiments tested a 40% and an 80% Schizochytrium sp. substitution against a 100% live algae control. In the first experiment, Tetraselmis suecica was used as a live algae control of moderate to poor nutritional value. Significantly higher growth over control was obtained with 40% Schizochytrium sp. substitution in C. gigas and 40% and 80% Schizochytrium sp. substitution in T. semidecussata. For the second experiment, equal portions of T. suecica and Chaetocerus sp. were used as live algae control of high nutritional value. The growth rate of both C. gigas and T. semidecussata controls increased over 600% on the mixed live algae diet as opposed to the first experiment with only T. suecica. Significantly lower growth rate was found for C. gigas at both 40% and 80% substitution. However, no significant growth difference was found for the T. semidecussata at 40% substitution in contrast to a significantly lower growth compared to control at 80% substitution. The results suggested that Schizochytrium sp. as a partial replacement for live algae in bivalve culture is economically viable, depending on the unit production cost of the live algae for any given nursery facility. (DBO)