Reproductive and immuno-biochemical response of silver barb (Barbonymus gonionotus) fed dietary l-tryptophan

Abstract

Tryptophan (Trp) influences several physiological functions, including reproduction, stress and immune function in fishes. The present study investigates the effect of dietary Trp supplementation on growth, reproduction, health of Silver barb, Barbonymus gonionotus. A basal diet (control/T1) with varying level of L-Trp at 0.4% (T2), 0.8% (T3) and 1.6% (T4) were fed to experimental fishes (71.04 ​± ​1.62 ​g) for 60 days period. Results indicate higher growth in groups fed 0.4% L-Trp compared to control (p ​< ​0.05). Percent survival was found to be low in all fed groups; however, 0.4% L-Trp (83.33 ​± ​3.33) was not significant as compared to control (93.33 ​± ​3.33). Significant effect (p ​< ​0.05) of dietary L-Trp was evident on the expression level of GnRH-II gene, with 6.26-fold-changes observed at 0.4% level. Reproductive functions (gonado-somatic index, fecundity and egg diameter) were better in groups fed 0.4% L-Trp (p ​< ​0.05). Ovarian histology indicates advanced maturation in fed groups, compared to the control. However, plasma melatonin showed elevated level in 0.8% and 1.6% L-Trp fed groups (p ​< ​0.05). Hemato-biochemical indices as a measure of the health status of the fish indicates elevated total leukocyte and decreased erythrocyte counts in fed groups (p ​< ​0.05). Blood glucose was lower (48.11 ​± ​1.63 ​mg. dl⁻¹), whereas respiratory burst activity (0.60 ​± ​0.02) was higher in 0.4% Trp compared to other groups (p ​< ​0.05). In conclusion, dietary L-Trp supplementation at 0.4% helps to augment growth performance in Silver barb, besides improving reproductive performance.