ENHANCED GROWTH OF THE GIANT CLAM, TRIDACNA-DERASA (RODING, 1798), CAN BE MAINTAINED BY REDUCING THE FREQUENCY OF AMMONIUM SUPPLEMENTS

Juvenile giant clams, Tridacna derasa (Roding, 1798), of 14-17 mm shel l length were exposed to no (control), two, three, or five additions o f 40 mu M ammonium sulfate per week in mass culture conditions for 45 days. Growth of clams, in terms of increase in wet weight and shell le ngth, was significantly greater in the ammonium-enriched conditions co mpared with the control; however, no significant differences in growth occurred among juveniles exposed to ammonium for 2, 3, or 5 days/wk. Mean density of zooxanthellae per clam also increased significantly wi th increasing frequency of ammonium addition. The degree of fouling by epiphytic algae (Boodlea sp. and Enteromorpha sp.) was significantly greater in tanks receiving ammonium 5 days/wk than in tanks receiving ammonium twice per week. These results indicate that supplementing wit h ammonium sulfate 2 days/wk is sufficient to maintain high growth rat es during land-based culture of juvenile T. derasa. The reduced freque ncy of these nutrient supplements also helps alleviate algal fouling i n rearing tanks.