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

I. Opstad, M.B. Rust-2004

Aquaculture Research, 35(13): 1286-1291 

Abstract:

First-feeding halibut larvae (245-day degrees; 40 days post hatch), reared at 34 g L^-1 salinity and 7°C, were subjected to handling and allowed to recover in a range of salinities (0-34 g L^-1) and at 10°C. 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=

-0.002x²+0.0603x+0.0699, r²=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.

(Institute of Marine Research, Austevoll, N-5392 Storebø, Norway. E-mail: ingegjerd.opstad@imr.no)

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