Can dietary manipulation mitigate extreme warm stress in fish? The case of European seabass, Dicentrarchus labrax

Abstract

Extreme climatic events affect all living organisms, including fish. This study evaluated growth, hematological, immune-antioxidant, and molecular stress responses to understand the acclimatization ability of European seabass, Dicentrarchus labrax fed on four different dietary supplements with subsequent exposure to an extreme ambient warm (32 oC) event. Fish were fed on diets supplemented with vitamins C (0.40%) and E (0.35%), propolis (0.45%), phycocyanin (0.30%), and β-glucan (0.30%) along with a control diet for 56 days, followed by 18 days of extreme warm exposure. Fish growth performance and survival were higher in fish fed on propolis followed by vitamins C & E and phycocyanin supplemented diets compared to fish fed on the control diet. During extreme warm exposure, red blood cells (RBC), hematocrit, hemoglobin, respiratory burst (RB), serum lysozyme activities (LSZ), and insulin-like growth factor 1 (Igf1) were significantly (P < 0.05) higher in fish fed on diets supplemented with propolis, vitamins C & E, and phycocyanin compared to fish fed on control diet. On day 18 of extreme warm stress, blood glucose and lactate levels were significantly higher in fish fed on control and β-glucan supplemented diets compared to the other three tested diets. On days 9 and 18, erythrocytic cellular abnormalities (ECA) and nuclear abnormalities (ENA) were significantly increased in fish fed on control and β-glucan diets (P < 0.05). Heat shock protein 70 (HSP70) and serum antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR)] activities were comparatively lower in fish fed on propolis and vitamins C & E supplemented diets compared to the control diet on days 9 and 18 of extreme warm stress. Most of the repeatedly measured parameters indicated that European seabass fed on diets supplemented with propolis, vitamins C & E, and phycocyanin provide improved acclimation potential during extreme ambient warm (32°C) exposure.