Effect of dietary seaweed supplementation on growth performance, antioxidant and immune responses in European seabass (Dicentrarchus labrax) subjected to rearing temperature and salinity oscillations

The current study evaluated the effects of dietary seaweed supplementation in European seabass juveniles (Dicentrarchus labrax) subjected to rearing temperature and salinity oscillations, simulating natural variations in pond aquaculture conditions. Two experimental diets where formulated: a control diet (CTRL) with no supplementation and one supplemented with 7.5% seaweed mix (SW 2.5% Fucus sp., 2.5% Gracilaria sp. and 2.5% Ulva sp.). Seabass from both dietary groups (40.7g initial body weight) was subjected to either combined salinity and temperature oscillations, or to fixed conditions. Growth performance, innate immune, and oxidative stress responses were evaluated. Results showed that seaweed supplementation had no significant effect on the analyzed parameters. However, environmental oscillations revealed significant effects on growth performance and oxidative stress response. Fish subjected to salinity and temperature oscillations had a significantly lower weight gain and daily growth index than those subjected to fixed conditions, regardless of dietary treatment. Total glutathione, oxidized glutathione, and catalase increased in fish subjected to oscillatory conditions. Lysozyme and peroxidase were not influenced by either diet or environmental conditions. In conclusion, this particular dietary seaweed mix supplementation did not mitigate the negative effects of environmental oscillations on growth performance and innate immune responses in European seabass.