Comparative growth and survival of juvenile hard clams,Mercenaria mercenaria,fed commercially available diets

Hobbyist and researchers often use commercially available phytoplankton concentrates to maintain filter feeding organisms held in their ornamental or experimental tanks. This study investigated the nutritional value of 10 products available commercially for juvenile hard clams, Mercenaria mercenaria. Growth and mortality rates in clams fed these products were compared with those found in clams fed fresh cultures of the microalgae Isochrysis galbana, which is considered an industry standard for supporting growth of juvenile bivalves. Our results show a clear difference in feed nutritional value between non‐living and living commercial diets, and among commercial diets advertised as containing live algae. Overall, results showed that juvenile hard clams fed fresh cultures of I. galbana displayed the best growth and lowest mortality rates, followed by those fed the commercial diet DT's Live Marine Phytoplankton. Growth and mortality rates in unfed controls were similar to those found in clams fed commercial non‐living algae mixes or diets advertised as containing live algae (Phyto‐Feast Live product). Results also showed that the nutritional value of fresh algae (I. galbana) cultures is lost rapidly when cultures are maintained at 4°C, suggesting that algae present in some commercial diets may lose their nutritional value during processing or refrigerated storage. The commercial blend, DT's Live Marine Phytoplankton, seems to represent a good substitute to lab grown algae for clams held in ornamental or experimental aquariums. Zoo Biol 0:1–13, 2006. © 2006 Wiley‐Liss, Inc.