Influence of diet on survival, growth, and physiological condition of fingernail clams Musculium transversum

The effects of diet and laboratory holding time on survival. growth, and ph ysiological condition of fingernail clams Musculium transversum were evalua ted in a 112-day study. The diets included a commercial oyster diet, a susp ension of commercial rabbit pellets, a suspension of fine, organic-rich sed iment, and a complete sediment renewal every 14 days. Sediment and clams we re obtained from a relatively uncontaminated site in the Upper Mississippi River. The experimental design consisted of 18 370-mL beakers per diet, eac h containing 5 cm of surficial sediment and 15 clams. Survival of clams was measured daily in each unit. Three units from each dirt were randomly remo ved on days 7, 14, 21, 28, 56, and 112, and clams were measured for shell l ength. Glycogen and cellulase activity were measured in composite samples ( 5 clams per sample) at each of the six time intervals. Cellulase activity d id not vary among diets or with time. Survival, growth, and glycogen varied significantly among diets, and glycogen concentrations varied with time, r egardless of dirt. Clams exposed to the two sediment diets were 2.4 times m ore likely to survive than clams exposed to the commercial diets. Survival of clams in all diets exceeded 80% through day 21. Although clams maintaine d an acceptable survival rate for 21 days, their physiological condition wa s compromised much earlier, given that glycogen reserves were reduced by 14 -54% after only 7 days. Thus, laboratory tests with fingernail clams should include physiological measures, in addition to survival: to ensure that cl ams are in suitable condition before and during testing.