Growth performance and thyroid hormones of Caspian kutum, Rutilus frissi, juveniles in response to dietary carbohydrate levels

Abstract

The aim of this study was to evaluate the effects of a practical diet containing different carbohydrate levels on growth rate, feed utilization, and thyroid hormones (T3 and T4) of Caspian kutum fingerlings. Fish with an initial average weight of 0.8 ± 0.2 g were fed five formulated isonitrogenous and isoenergetic diets with different carbohydrate levels of 15, 20, 25, 30 and 35 % in triplicate groups for 10 weeks. Based on the results, growth performance of <em>Rutilus frissi</em> was significantly affected by the dietary carbohydrate levels (<em>P</em> < 0.05). Maximum weight gain, specific growth rate, and protein efficiency ratio was observed in the fish fed diet with 35 % carbohydrate. Results of thyroid hormones showed that T4 levels were not significantly different by different carbohydrate levels (<em>P</em> > 0.05). The highest amount of T4 was observed in kutum juveniles fed with a carbohydrate level of 15 %. The levels of T4 were significantly affected by dietary carbohydrate levels (<em>P</em> < 0.05) with the highest amount in kutum juveniles fed 15 % of carbohydrate. In conclusion, this study indicates that increasing carbohydrate levels from 15 to 35 %, with no negative effects on growth parameters in <em>R. frissi</em> juveniles, leads to an efficient protein ratio and optimal growth. Moreover, no clear correlation was found between fish growth and thyroid hormones.