Manipulated yeast diets and dried algae as a partial substitute for live algae in the juvenile rearing of the Manila clam <i>Tapes philippinarum</i> and the Pacific oyster <i>Crassostrea gigas</i>

The development of a cost-effective artificial diet would greatly reduce the operating costs and improve the efficiency of bivalve seed production. The present study documents the use of a manipulated yeast diet and dried algae (Tetraselmis suecica, Cyclotella cryptica) as an 80% substitute for live algae under the conditions of a commercial bivalve hatchery. Juveniles of the Manila clam T. philippinarum and of the Pacific oyster C. gigas were grown in a 28l recirculating system for three weeks. In addition, a preliminary flow-through culture test was performed with C. gigas. Supplementing manipulated yeasts improved the growth rate of juvenile clams and oysters fed 20% of the algal ration from 30-40% to 70-80% of that observed for the algae-fed controls over a period of 3 weeks. The yeast diet supported similar clam growth as the dried T. suecica and better oyster growth than the dried C. cryptica. Substituting 80% of the algal ration by either the yeast diet or dried T. suecica in the flow-through experiment with C. gigas resulted in a growth rate exceeding 90% of that observed for the algae-fed controls during the first week of the experiment. During the second week of the test this relative growth rate was only maintained by oysters fed the 20/80% algae/dried T. suecica diet. Further research is needed to define the optimal food levels of the yeast diets in continuous flow cultures