Introduction
In the current scenario, global climate change is a reality that impacts all living species, including fish. The aquatic ecosystem, since it is the largest sink for global warming and high temperatures, is the most affected system and affects all types of aquatic life.
Materials and methods
Fish were fed on diets supplemented with vitamin 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. Growth performance, individual fitness, metabolic activities, nutrient assimilation capacity, and molecular stress respons es were evaluated to understand dietary manipulation impacts .
Results
Final weight gain, weight gain, specific growth, and protein efficiency were higher in fish fed with propolis followed by phycocyanin, vitamin C & E, and β-glucan compared to the control diet. Besides, viscera somatic index, intestine somatic index, and hepatosomatic index values were higher in the control diet compared to tested diets. Significantly higher Na+ and Cl- levels were measured (p<0.05) in fish fed to control diet followed by vitamin C & E, propolis, phycocyanin, and β-glucan. While K+ ion level was found significantly lower (p<0.05) in fish fed with control and β-glucan supplemented diets during heatwave stress. Cholesterol and triglycerides levels were found signifi cantly lower (p<0.05) in fish fed on vitamin C & E, propolis, and β-glucan supplemented diets compared to fish fed on the control diet. Blood urea nitrogen, creatine, and cortisol content were significantly lower (p<0.05) in fish fed with vitamin C & E, propolis, and phycocyanin supplemented diets compared to fish fed on the control diet. AST, ALT, and LDH contents were found higher in fish fed on Vitamin C & E supplementation followed by propolis, control, phycocyanin, and β-glucan supplemented diets. Transcriptomics result also supports the better health and physiological conditions in fish fed on vitamin C & E, propolis, and phycocyanin supplemented diets.
Discussion and conclusion
Diets with the increased dosage of Vitamins C and E, propolis extract, and phycocyanin were found to be beneficial for European seabass, Dicentrarchus labrax during extreme warm exposure. Diets containing high levels of either vitamin E (4.0 g kg-1) together with high levels of vitamin C (3.5 g kg-1), or propolis (4.5 g kg-1), or phycocyanin (0.30 g kg-1) were able to counteract the adverse effects of stress responses during extreme warm exposure. To some extent, these ingredients were found to improve fish growth, antioxidant capacity, and immune functions. In contrast, the inclusion of dietary β-glucan was found to be less functional in supporting fish growth, physiology, and metabolism.