Dietary orange peel fragment, zinc and vitamins C and E supplementation effect on growth, antioxidant enzyme activity, hemato-immunological responses of Nile tilapia subjected to temperature, transport and bacterial challenges

Abstract

This study aims at evaluating the supplementation of orange peel fragment, vitamins C and E and zinc on growth performance, hematological profile, immunological parameters, gene expression and antioxidant enzyme activity of Nile tilapia juveniles subjected to heat-dissolved oxygen induced stress and bacterial challenge. This research was divided into two distinct phases. In phase I, Nile tilapia juveniles will be fed four times a day to apparent satiation with one of the following diets: basal diet (BD) + 0.6% orange peel fragment, BD + 0.6% orange peel fragment + 600 mg kg-1 vitamin C, BD + 0.6% orange + 200 mg kg-1 vitamin E, BD + 0.6% orange peel fragment + 79.51 mg kg-1 zinc, BD + 600 mg kg-1 vitamin C + 200 mg kg-1 vitamin E, BD + 600 mg kg-1 vitamin C + 79.51 mg kg-1 zinc, BD + 200 mg kg-1 vitamin E + 79.51 mg kg-1 zinc, BD + 0.6% orange peel fragment + 600 mg kg-1 vitamin C + 200 mg kg-1 vitamin E + 79.51 mg kg-1 zinc. In this phase, a group of 600 Nile tilapia juveniles will be distributed in 40-250L aquaria in a completely randomized design with eight treatments and five replicates. After 90 days, growth performance, intestinal microscopy, muscle oxidation, hematological profile, immunological parameters and antioxidant enzyme activity will be evaluated. In phase II, one fish group will be subjected to heat/dissolved oxygen and another one to bacterial challenges. As to heat-dissolved oxygen induced stress, 20 fish/treatment will be subjected to 35°C for three days. Then, for the 15-day bacterial challenge, fish/treatment will be infected with Aeromonas hydrophila. Before and after both challenges, the following parameters will be evaluated: hematological profile, immunological parameters and antioxidant enzyme activity. Based on the data obtained at phases I and II, the best treatment will be chosen for Nrf2 gene expression analysis will be chosen. This analyses will be performed in the liver samples from fish fed the best treatment and basal diet for comparison. Data for each parameter will be tested for normality and homoscedasticity. One-way analysis will be used to evaluate the growth performance (P < 0.05) followed by Tukey test. The hematological profile, immunological parameters, antioxidant enzyme activity and gene expression will be analyzed using non-parametric test (Kruskal-Wallis) together with Mann-Whitney test (P < 0.05). (AU)