Determination of critical thermal minima and maxima of european sea bass (Dicentrarchus labrax) in different salinity and temperature levels

This study was carried out to determine upper (CTMax), lower (CTMin) thermal tolerance, acclimation response ratio (ARR) and thermal tolerance polygon of the European Sea Bass (Dicentrachus labrax) inhabiting the north-eastern Mediterranean at three acclimation temperatures (15, 20, 25°C) and three salinity levels (0, 20 and 38 ppt). The data showed that acclimation temperature, salinity and the intereaction of both parameters significantly affected the CTMin and CTMax values of the fish (P<0.001). At 0.3 ? C min-1 cooling or heating rate, CTMin ranged from 3.26 to 7.33 ? C and CTMax ranged from 32.01 to 36.68 ? C. Thermal tolerance polygons for the juveniles at 0, 20 and 38 ppt were calculated as 272.69, 291.95, and 296.14°C2, respectively. The calculated ARR values for 15-20°C and 20-25°C were 0.08-0.68 and 0.14-0.42, respectively. In three acclimation temperatures (15, 20, 25°C), the overall ARR values ranged between 0.23 and 0.54. Our sea bass strain from the Northeastern Mediterranean appeared to be more tolerant towards lower but less resistant to upper temperatures. The cold tolerance zone attained in this study for the juveniles ranged from 3.26 to 7.33 ? C and high temperature tolerance zone ranged from 32 and 37°C. In the case of deeper ponds and high water exchange rates, cold winter temperatures may not pose danger during the culture of European sea bass in ponds. Upper thermal tolerance is more of a problem as maximum water temperature may sometimes exceed 33-34 ? C, and hence care should be given if there is no cool water to lower ambient water temperature in the mid-summer in such areas.