INFLUENCE OF TEMPERATURE AND FOOD AVAILABILITY ON SURVIVAL, GROWTH AND YOLK UTILIZATION IN HATCHLING SQUID

摘要

Loligo opalescens eggs were incubated and the hatchlings were reared at two temperatures (12°and 16℃). At each temperature, there were two groups of hatchlings (n = 600). Food was supplied to one group (Fed) while no food was supplied to the other (Starved). Yolk volume and dry and wet weights were obtained daily from each group (n = 7). Measurements of the yolk sac made by image analysis were converted into volume; mean daily yolk volumes were converted into weights. Compared with hatchlings reared at 16℃, those at 12℃ were heavier (0.64 mg dry weight vs 0.44 mg), had more yolk (0.38 mg vs 0.19 mg), absorbed yolk two times slower and, when starved, survived longer (6 d vs 4 d). The yolk-weight to body-weight ratio at hatching was not significantly different between the two temperature groups, indicating that the amount of yolk is proportional to body weight. Higher yolk utilization rates were found for Starved hatchlings, suggesting that Fed and Starved hatchlings consumed their yolk at different rates and that yolk utilization is dependent of the feeding condition. Yolk utilization appeared to be most efficient at 12℃, resulting in the largest hatchlings after complete yolk utilization but growth rate and survival were reduced. Early growth of hatchlings uncovered a phase with no net growth that lasted 10―15 d. High mortalities during this 'no net growth' phase reveal a critical period in the early life history of squid. Exponential growth began only after 10―15 d post hatching. Results are interpreted in relation to temperature variation during El Nino events.