Dietary nucleotide supplements influence the growth, haemato-immunological parameters and stress responses in endangered Caspian brown trout (Salmo trutta caspiusKessler, 1877)

A feeding trial was conducted to evaluate the effects of Optimûn, a commercial nucleotide (NT) product, on the growth, haemato-immunological and serum biochemical parameters and stress responses of Caspian brown trout fingerlings (average initial weight of 12.26 g). A basal diet was supplemented with levels of 0 (control), 1.5, 2.5, 3.5 and 5 g NT kg−1 to formulate five experimental diets. After 8 weeks of feeding trial, fish fed diet with 2.5 g NT kg−1 had the highest final weight compared with other treatments. The fish fed diets with 2.5 g NT kg−1 had higher blood protein, albumin, albumin/globulin ratio, red blood cells, white blood cells and lymphocyte content and lower alkaline phosphatase. The lysozyme activity in serum was found to be significantly (P < 0.05) greater in fish fed diet with 2.5 g NT kg−1. Concerning both stressors (confinement and salinity stress), fish fed diet with 2.5 g NT kg−1 had lower plasma cortisol and glucose levels. Thus, administration of 2.5 g kg−1 of the Optimûn dietary nucleotide formula is recommended to promote growth and immunity as well as to enhance stress responses of Caspian brown trout.