Heat stress is one of the consequences of climate change which has devastating effects on fish farming especially in intensive systems, resulting in huge economic losses. The aim of this study was to evaluate whether dietary supplementation with free- or nano-form of curcumin improves growth performance, immune status, and heat stress resistance in Nile tilapia (Oreochromis niloticus).
Seven diets were prepared, six of which contained 3 levels of curcumin nano-sphere (50 (CN50), 100 (CN100) or 200 (CN200) mg kg-1) or free curcumin (50 (C50), 100 (C100) or 200 (C200) mg kg-1), and one diet contained no addition (CON). Fish (13.54±0.32 g) fed the experimental diets for 65 days and then they subjected to the acute heat stress by gradually raising the water temperature from 25 to 40? within 3 h. Results revealed that dietary curcumin has enhanced growth performance with superiority to nano-curcumin over the free form. The optimum growth performance was obtained at CN100 (Fig.1). Heat stress rather than diets increased platelets, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), leukocytes and neutrophils counts while lymphocytes decreased. CN50 and CN100 reduced the activity of liver enzymes (Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) more efficiently than the other diets and C200 gave the highest activity of these enzymes. CN100, CN200, C100 and C200 had higher immunoglobulin (IgM) levels than CN50 while C50 and CON gave the lowest values. C200 showed a higher level of complement C3 and C4 than the other treatments while C50 and CON gave the lowest values (Table 1). CN50 and CN100 have efficiently eliminated cortisol levels compared to the other treatments. All curcumin-supplemented diets, except for C200, produced lower glucose values compared to CON. After heat stress, ALT, AST, IgM, C3, C4, cortisol and glucose have been increased. Thus, curcumin nano-sphere has better ability than its free form to increase the ability of farmed fish to withstand heat stress, enhance growth rates and thus increase fish productivity