Bacteria-free Culture of Oyster Larvae

Abstract

LARVAL cultures of many marine bivalve molluscs have been maintained through stages leading up to metamorphosis and the principal requirements are now known, particularly for the European oyster Ostrea edulis L., the American oyster Crassostrea virginica (Gmelin) and the American clam Mercenaria mercenaria (L.). It is common experience that cultures may fail unexpectedly and there is evidence that bacterial contamination is often the cause1,2. In this laboratory we have also had inconsistent results and sudden mortalities, and have found that bacterial counts vary greatly and are often high, even when antibiotics are used. Although antibiotics reduce the percentage of failures, Hidu and Tubiash3 have shown that streptomycin, which is commonly used for this purpose, can increase the total bacterial number; its beneficial effect is to limit harmful bacteria and to increase useful types. The use of antibiotics leads to levels of success that would be acceptable in hatchery work, but it is evident that critical experiments in larval nutrition, in genetic and environmental effects on growth and other aspects of larval biology, will depend on the elimination of the variable factor represented by the presence of bacteria. We have therefore investigated methods of growing the larvae of O. edulis in the absence of bacteria.