Boeing, P., Freeman, M.
Abstract:
Two commercially important species of juvenile bivalves (Tapes semidecussata and Crassostrea gigas) were fed a spay-dried preparation of heterotrophically grown algae, Schizochytium sp. in 20 liter recirculating downwell systems. All systems were fed a weekly ration equal to 50% of their live wieght as dry weight calculation for live algae or percentage Schizochytrium sp. substitute. Weekly growth rates of juveniles as live wet weight increase and an initial and final condition index as free dry weight were measured to determine the effects of the different diets. Two experiments were performed in duplicate, the first using Tetraselmis suecica, a live algae control of moderate nutritional value, and the second using an equal mixture of Chaetocerous sp. and Tetraselmis suecica, a live algae control of high nutritional value. In the first experiment, 40% and 80% substitution for live algae T. suecica were compared to controls fed 100% live T. suecica. Significantly higher growth over the control was obtained with 40% substitution in C. gigas and 40% and 80% substitution in T. semidecussata. For the second experiment, 40% and 80% substitution for equal portions of live algae Chaetocerous sp. and T. suecica mixture were compared to controls fed 100% live algae mixture. Significantly lower growth rates were found for C. gigas at both 40% and 80% substitution. However no significant growth difference was found for T. semidesussata at 40% substitution, in contrast to a significantly lower growth over the control at 80% substitution. These results suggest that the routine use of Schizochytrium sp. (ALGAMAC-2000, Aquafauna Bio-Marine, Los Angeles, CA.) as a partial replacement of live algae in bivalve culture to be an economically viable alternative, depending upon the unit production cost of the live algae for any given nursery facility.
(Pacific Seafarms International S.A. de C.V., Cerro Escondido No 122, Mazatlan, Sinaloa, Mexico)
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