Effect of recovery salinity on survival of acutely stressed halibut (Hippoglossus hippoglossus L) larvae

摘要

First-feeding halibut larvae (245-day degrees; 40 days post hatch), reared at 34 g L-1 salinity and 7degreesC, were subjected to handling and allowed to recover in a range of salinities (0-34 g L-1) and at 10degreesC. Survival of the unfed larvae was determined daily for 18 days. Mortality rates approached 0 after 4 days in all treatments and presumed starvation-induced mortality started at about 11 days post handling. By 20 days post treatments, all larvae had died. Salinities in the range of 10-20 g L-1 produced significantly (ANOVA, P<0.01) higher initial survival (71-95%) than salinities above 20 g L-1 (24-48%) or below 10 g L-1 (0-19%) and this survival pattern changed little in unfed larvae for the first 10 days following the stressor. For example, 24 hour post handling, survival of halibut was improved from 28.7+/-16.5% (mean+/-standard error, n=3) at 34.0 g L-1 to 95.2+/-4.8% at 13 g L-1. A second-order polynomial regression of 4-day post-handling survival data (y=-0.002 (x) under bar (2)+0.0603x+0.0699, r(2)=0.3936) predicted a maximum survival at 15.1 g L-1 salinity. These results have important implications for halibut aquaculture and research when handling of larvae is unavoidable. For practical applications, we recommend reducing salinity of receiving waters to 15-20 g L-1 with a slow (3-4 days) reacclimation to ambient conditions.