There is evidence that extreme weather events are becoming more frequent and intense than ever as a result of climate change. To date, studies revealing the modulation of hemato-physiological potential as a compensatory response to extreme warm events combined with different salinities are rather lacking. To elucidate the extreme warm event impacts on European seabass, Dicentrarchus labrax acclimated at different salinities, the study aimed to assess the growth performances, hemato-physiological response and molecular response of European seabass.
Fish reared at 32 ppt and 2 ppt showed significantly (P<0.05) lower final body weight (FBW), weight gain (WG), specific growth rate (SGR), and protein efficiency ratio (PER) compared to fish maintained at 12 ppt and 6 ppt. Significantly (p<0.05) higher mortality rate was observed for fish at 30 ppt and 2 ppt during the 10 days of extreme warm acclimation periods. Similarly, the condition factor (CF) value was also influenced by salinity and temperature stress. Overall, all the growth performance and feed utilization parameters were significantly lowest in fish reared at 30 ppt and 2 ppt, followed by exposure of 10 days warm extreme (33oC). A significant (P<0.05) reduction of VSI, ISI, HIS, SSI was observed in fish reared at 2 ppt (Table 1). RBCs, hematocrit, and hemoglobin content were significantly decreased, while WBCs, erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) were found to increase in 32 ppt and 2 ppt fish.
With the progression of extreme warm stress, plasma glucose tended to decrease in all salinity groups. Plasma lactate was found to increase significantly (p<0.05) in 32 ppt fish on day 10. Glutathione peroxidase (GPx), glutathione reductase (GRx), superoxide dismutase (SOD), catalase (CAT) and TNF-α expression increased significantly (p<0.05) in fish reared at 32 ppt and 2 ppt fish. Overall results indicate that growth, erythrocytic abnormalities, antioxidant activities and gene expression mediated by the experimental conditions were exacerbated in European seabass during extreme warm exposure.
This study suggests that low salinity acclimation particularly at 12 ppt and 6 ppt salinities, fish can cope better during extreme warm exposure. However, none of the repeated measured parameters in this study indicated the adaptation and compensation capacity through physiological adaptation over the 10 days of extreme warm exposure.