Dietary nucleotide supplements influence the growth, haemato‐immunological parameters and stress responses in endangered C aspian brown trout ( S almo trutta caspius K essler, 1877)

A feeding trial was conducted to evaluate the effects of O ptimûn, a commercial nucleotide ( NT ) product, on the growth, haemato‐immunological and serum biochemical parameters and stress responses of C aspian 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 O ptimûn dietary nucleotide formula is recommended to promote growth and immunity as well as to enhance stress responses of C aspian brown trout.