Impact of varying cultivation depths on growth rate and survival of the European flat oyster Ostrea Edulis, L.

European oysters, Ostrea edulis, L. were kept in plastic mesh cages at three depths at two commercial oyster farm sites within Mali Ston Bay, Croatia, between April 2004 and August 2005. Oysters from each cultivation depth were sampled at both sites at approximately 3‐month intervals for growth parameters, mortality rate control and condition index calculation. The growth parameters of experimental groups from both sites only revealed a considerable distinction for shell length growth (P=0.011). Total weight gain and soft tissue weight gain were the highest for groups cultivated in the middle of the water column as compared with the top and bottom positions for both studied sites. Survival rates were very similar in all experimental groups, situated at different depths of both experimental sites, and differences in the mortality peak during the summer months were not significant. Condition indices fluctuated throughout the trial period and were the highest in spring and summer, with a reduction during the winter months and improvement again in the spring.