Optimizing survival, growth and feeding in hatchling squid (Loligo opalescens)

The present study investigated survival, growth and feeding during the early life history of the market squid, Loligo opalescens. Survival was improved by: (1) maintaining current speed between 1.0--1.4 cm s-1 to reduce problems with skin and fin damage; (2) feeding enriched Artemia nauplii during the first 30 days; and (3) feeding a variety of prey to match the different sizes and hunting abilities of same-aged but heterogeneously developing hatchlings. Survival rates obtained were between 35% and 60%. To investigate the effect of temperature on the survival, growth and rate of yolk utilization of fed and starved hatchlings, they were reared at 12 and 16°C. In contrast to squid hatched at 16°C, squid hatched at 12°C were heavier (0.64 mg dry weight; 0.44 mg at 16°C), had more yolk (0.38 mg; 0.19 mg at 16°C), absorbed yolk two times slower and when starved survived longer (6 days; 4 days at 16°C). There was no significant difference in the rate of yolk utilization between the fed and the starved groups within each temperature, suggesting that this rate was independent of the feeding condition. Within the first 10--15 days no growth occurred in the fed groups since hatchlings lost more weight due to yolk utilization than they could gain back by feeding. The ability of hatchlings to recover from starvation was examined by measuring their survival, growth and RNA:DNA ratio. The limit to recovery for 15 day old hatchlings reared at 16°C was 3 days of starvation. For hatchlings starved 2 and 3 days it took from 2 to 3 days after refeeding to attain the same RNA:DNA ratios as the control. Significant differences in the RNA:DNA ratio between control and starved hatchlings were detected after 3 days of starvation. Hatchlings starved for 2 and 3 days showed compensatory growth that mitigated the effects of starvation. Additionally, RNA:DNA ratios were highest during the day (0800, 1200 hr) and lowest at night (0000, 0400 hr) indicating daytime feeding activity. The tentacles of hatchlings are noncontractile. Thus, the tentacular strike behavior characteristic of the adults was first observed in 40 days old hatchlings.