Effects of dietary lysine level on the growth performance, protein metabolism, and antioxidant status in Hemibagrus wyckioides juveniles

Abstract

An 11-week feeding trial was conducted to assess the dietary lysine requirement for juvenile Hemibagrus wyckioides. Six isoproteic and isoenergetic diets (41.66% crude protein, 20.56 kJ/g gross energy) containing 1.1%, 1.5%, 1.9%, 2.3%, 2.7%, and 3.1% lysine were prepared to feed juveniles (average initial body weights of 1.25 g), respectively. The weight gain, specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio significantly improved with the dietary lysine level up to 2.3%, 1.9%, 2.3%, and 2.3%, and then plateaued afterwards. The highest midgut trypsin and lipase activities as well as plasma antioxidant enzyme activities and nitric oxide content but the lowest plasma malondialdehyde content were recorded in fish fed diet with 2.3% lysine. Fish fed diets with 1.9% or 2.3% lysine exhibited the highest plasma total protein and insulin contents, the lowest plasma ammonia content, and relative expression levels of glutamate dehydrogenase in the liver and adenosine monophosphate deaminase in the liver and muscle. Similarly, fish-fed diet with 2.7% lysine showed the lowest hepatic alanine aminotransferase activity but the highest hepatic expression level of the mammalian target of rapamycin. Broken-line regression analysis based on SGR and FCR showed that the dietary lysine requirement for juvenile H. wyckioides was 2.04% to 2.09%, while dietary lysine of 2.3% was optimum for the antioxidant status of H. wyckioides.