Effects of dietary supplementary leucine in a wheat meal‐rich diet on the growth performance and immunity of juvenile gibel carp ( Carassius auratus gibelio var. CAS III)

Abstract

Leucine has been reported to regulate key metabolic pathways, including growth, immunity and antioxidative defence. To study the effects of dietary leucine supplementation in a carbohydrate‐rich diet on juvenile gibel carp (Carassius auratus gibelio var. CAS III), an 8‐week feeding trial was conducted on gibel carp juveniles reared on an experimental wheat meal‐rich diet (40%) with varying leucine contents (0.87%, 1.23%, 1.68%, 2.10%, 2.41% and 2.83%). No significant changes in growth performance were observed regardless of leucine levels (p > 0.05). However, proper leucine levels (1.68% and 2.10%) could increase the accumulation of whole‐body crude protein and decrease the accumulation of crude lipid. Furthermore, significant liver tissue damage occurred at 1.23% and 1.68% dietary leucine levels, whereas 2.10% and 2.41% dietary leucine could improve the antioxidant capacity at the end of the 8‐week feeding trial. 1.68% and 2.10% dietary leucine levels could alleviate the hyperglycaemia caused by high carbohydrate intake after the 8‐week feeding trial, as well as the elevated glucose content after starvation, to maintain normal metabolic conditions. Supplementation with leucine could significantly downregulate IL‐1β, TNF‐α1, MyD88 and TIRAP mRNA levels during the 8‐week feeding trial and after starvation for 48 h. In conclusion, 2.10%–2.41% leucine contents in a carbohydrate‐rich diet could benefit muscle protein deposition, hyperglycaemia and hyperlipidaemia alleviation, and results in non‐specific immunity improvement.