Oyster spat were cultured for 21 day periods in plastic trays hanging at the surface of 50 1 tanks. The water was continually recirculated through the trays and comparisons were made of the growth of oyster spat at various levels of feeding of the unicellular alga Tetraselmis suecica, the number of spat per litre of water, the number of spat per tray, flow rate through each tray, frequency of water change and water temperature. A factorial design was adopted so as to test all levels of each factor against the other factors. Food level had the greatest influence on growth and 1 to 3 mg increase in live weight was obtained for every 106 cells fed to a spat in the 21 day period. Between 10 to 20% of the food offered was converted into dry meat. The number of spat per litre was also important but only because of its influence on food supply. The number of spat per tray had a consistent effect but it was small compared with food supply. At higher temperatures, the growth of shell was relatively more rapid than that of the meat and this led to a decrease in the condition index.