Growth and survival of hybrid sunfish larvae in the laboratory under different feeding and temperature regimes

The objective of this study was to determine the effects of different feedi ng protocols and temperatures on growth and survival of hybrid fry of femal e green sunfish Lepomis cyanellus X male bluegill L. macrochirus. At swim-u p (5-6 d posthatch), we divided larvae into three different treatments: fee dings of brine shrimp Artemia franciscana for 0, 3, or 7 d followed by a 3- d weaning period to a commercial diet. We monitored fish growth and surviva l through 28 d posthatch. Significant differences in growth were not eviden t at 28 d posthatch, but survival in the 7-d treatment (mean, 37%; SE, 2.6% ) was significantly higher than that in the other treatments. In a second e xperiment comparing three different temperatures (19, 21, and 24 degreesC) and two feeding regimes (live brine shrimp for 3 and 7 d before weaning to commercial feed), temperature regimes did not significantly affect growth. At 28 d posthatch, larvae fed brine shrimp for 7 d were significantly longe r than those fed for 3 d. At 21 degreesC and 24 degreesC, larvae fed brine shrimp for 7 d were significantly heavier than those fed for 3 d. Within th e specific feeding regimes, larvae cultured at 21 degreesC were significant ly heavier than those at 19 degreesC and 24 degreesC. Survival (28% to 41%) did not differ significantly among the treatments. The initial brine shrim p feeding regime affects fish growth more than do temperatures within the 1 9-24 degreesC range. When using brine shrimp to culture larval green sunfis h X bluegill hybrids for at least 7 d, survival rates of approximately 40% can be expected.