CAN DIETARY MANIPULATION AMELIORATE EXTREME HEATWAVE STRESS IN FISH? THE CASE OF EUROPEAN SEABASS Dicentrarchus labrax

Global extreme climatic events impact all living organisms, including fish. This study aimed to evaluate the growth, hemato-physiological, and immune-antioxidant stress responses as indicators for the acclimatization ability of European seabass (Dicentrarchus labrax ) fed with four different dietary supplements, with subsequent ambient extreme heatwave (32 ^o C) exposure.

Fish were fed with diets supplemented with vitamin C and E, propolis, phycocyanin, β-glucan, along with a control diet for 56 days, followed by 18 days of extreme ambient warm exposure. Results indicated that fish growth performance and survival were higher in fish fed with propolis followed by vitamins C, E and phycocyanin supplemented diets (Table 1) .

During extreme warm exposure, red blood cells (RBC), hematocrit, hemoglobin, respiratory burst, and serum lysozyme activities were significantly higher in fish fed propolis, vitamins C, E and phycocyanin supplemented diets (p<0.05). On day 18 of extreme warm stress, blood glucose and lactate levels were significantly higher in control and β-glucan fed fish compared to other diets. On days 9 and 18, erythrocytic cellular abnormalities (ECA) and nuclear abnormalities (ENA) were significantly increased in control and β-glucan diets (p<0.05). Serum antioxidant enzymes' [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR)] activities were comparatively lower in fish fed propolis and vitamins C and E supplemented diets during days 9 and 18 of the extreme warm stress. Most of the repeatedly measured parameters indicated that diets supplemented with propolis, vitamins C & E, and phycocyanin provide improved acclimation potential during ambient extreme warm exposure (32 °C).