Responses of summer flounder, Paralichthys dentatus, embryos to thermal shock

Abstract

Summer flounder eggs, fertilized artificially, were exposed to time series of abrupt thermal shocks and examined for lethal and sublethal effects. The temperature increments (ΔTs) ranged from 8° to 20°C above the holding temperature, the periods of exposure to the ΔTs were for 2, 4, 8 and 16 minutes. Eggs were exposed at early embryo and late embryo stages of development. The eggs were found highly resistant to thermal shock, early embryo stage eggs survived the highest temperature-time exposure used, at ΔT 20°C for 16 minutes; late embryo stage eggs showed significantly increased mortalities in the region of ΔT 16° C for 16 minutes and ΔT 18° C for 2 minutes and at all higher temperature exposures. Larvae hatching from the late embryo stage eggs after thermal shock were examined for anomalous anatomical development. A pattern of increasing incidence of developmental anomalies appeared at ΔT 14°C after exposures of between 4 and 8 minutes. Such sublethal effects probably lead quickly to larval death from starvation, predation, etc., and must be taken into consideration in assessing effects of thermal shock.