The effects of larval stocking density on growth, survival, and development of laboratory-reared Spisula solidissima similis (Say, 1822)

The optimal larval stocking density was determined for laboratory-reared Spisula solidissima similis (Say). Stocking density treatments of 10, 20, 30, and 50 larvae/mL were analyzed for effects on survival, growth, and development. Twenty-four-hour-old larvae were stocked at the above densities in 500-mL flasks containing seawater at 25 ppt and 20 degree C. All treatments received a daily food ration of 100,000 cells/mL of Tahitian strain Isochrysis sp., with complete water exchange per flask every 2 days. Three replicates per treatment were subsampled (n = 5), on days 1, 5, 9, 15, and 27. No significant differences (p = 0.3539) in survival occurred between stocking densities at day 27, with percent survival ranging from 56% for the 10 larvae/mL to 35% for the 50 larvae/mL treatments. Larval size (in micrometers) was significantly different for all treatments on day 9 (p < 0.0001: 50, x super(-) = 88.4 mu m < 20, x super(-) = 95.0 mu m < 30, x super(-) = 101.8 mu m < 10, x super(-) = 117.0 mu m) and day 27 (p < 0.0001: 50, x super(-) = 145.8 mu m < 30, x super(-) = 175.6 mu m < 20, x super(-) = 195.7 mu m < 10, x super(-) = 263.0 mu m). A higher percentage of animals had completed metamorphosis at day 27 in the lower stocking density treatment of 10 (87%) than in the higher stocking density treatments of 20, 30, and 50 larvae/mL (10, 3.0, and 0%, respectively). Optimal stocking densities for cultured S. s. similis larvae are equal to or less than 10 larvae/mL.