Abstract:To study the effect of high temperature stress on the early development of turbot Scophthalmus maximus, the thermal tolerance of five early developmental stages of S.maximus was studied. The hatching stage embryo, yolk-sac larvae (0 days post hatching,0 dph ), preflexion larvae (10 dph), flexion larvae (25 dph) and juvenile (50 dph) of turbot were subjected to various temperatures from 22～33℃ for 2-hour heat shock, and then transferred to seawater at initial temperature (17.5℃) for 60～84 h. The mortality, larvae hatching rate and abnormal rate were recorded continuously. The results showed the sub-lethal temperature of early developmental stages of turbot were 24℃, 23℃, ＜22℃, 28℃, 28℃, respectively; the 50% mortality (LT50) temperature were 26℃, 28℃, 22℃, 29℃ and 29℃, respectively; and lethal temperature were 30℃, 29℃, 27℃, 30℃ and 30℃, respectively. Based on the experimental mortalities of turbot by heat shock after 24 h and 48 h, the order of thermal tolerance of turbot at five stages was 10 dph＜embryo＜0 dph＜25 dph＜50 dph. These results indicated that the thermal tolerance of turbot increased with the development and growth during the first 50 dph. The stage of 10 dph, the swim bladder developing stage, is the low-ebb period of thermal tolerance, and the larvae are sensitive to temperature heat shock at this stage.
