Evaluation of microalgae and industrial cheese whey as diets for Tapes decussatus (L.) seed: effects on water quality, growth, survival, condition and filtration rate

Abstract

As reference diets for bivalve molluscs are missing, this study first evaluated the best mixed algal diet (Tetraselmis suecica Butch/Phaeodactylum tricornutum Bohlin) concentration for 4-mm-length Tapes decussatus (L.) clams. It also assessed the performance of an industrial by-product (cheese whey) as a single diet or supplement for the best algal ration previously determined. Growth, survival, condition index and filtration rate were used to compare the different diets. Implications of rations tested on rearing water quality were also investigated, especially ammonium and heterotrophic bacteria levels. With a food concentration as algal dry weight per total seed live weight of 0.7% day−1, seed for grow-out (7 mm) could be obtained within 1 month. A mixture of 25% algal ration and 75% cheese whey gave the best performances. Artificial diets resulted in lower growth rates than live food (20 % to 40% of the best algal ration), but could be considered good maintenance rations in energetic terms. Using cheese whey, and without any algae, hatchery produced seed can be kept economically indoors for at least 30 days without loss in condition.