Effects of organic selenium supplementation on growth, glutathione peroxidase activity and histopathology in juvenile barramundi (Lates calcarifer Bloch 1970) fed high lupin meal-based diets

Very limited information is available on the relationship between dietary selenium (Se) and plant protein (PP) sources in carnivorous marine aquaculture species. Therefore, this study employed a 2 x 3 experimental layout to investigate the effects of lupin meal (LM) protein inclusion levels (0, 25 and 75%) and organic selenium (OS) levels (0 or 2 g kg(-1)) on the growth, physiology and histopathology of juvenile barramundi (Lates calcarifer). The experimental diets (LM0, LM0+OS, LM25, LM25+OS, LM75 and LM75+OS) were formulated on an isonitrogenous (48.8% crude protein) and isocalorific (20.6 MJ kg(-1) gross energy) basis. In the 60-day feeding experiment, final weight (FW), specific growth rate (SGR) and weight gain (WG) were improved by the supplementation of Se in LM-based diets. Fish fed diets containing Se had higher FW, SGR and WG compared with those fed diets lacking Se supplementation (P < 0.05). Both LM inclusion levels and Se supplementation levels affected the apparent digestibility coefficient of protein (ADC-P). Meanwhile, survival and the thermal growth coefficient (TGC) were not significantly different among all dietary treatments. The inclusion of a high LM level resulted in decreased glutathione peroxidase (GPx) activities, but this effect was not observed when Se was supplemented in the diets. Furthermore, there was a linear relationship between muscle Se level and Se concentration of the experimental diets. Se-induced myopathy was observed in skeletal muscles of fish fed LM diets without Se supplementation. In addition, structural alteration was found in the liver; however, the kidney, spleen and intestine were histologically normal. Overall, these results suggest that high LM diets supplemented with organic selenium can enhance growth, physiological and histological performances of juvenile barramundi. Statement of relevance: While plant-based feed sources such as lupin meal have the potential to reduce the reliance on unsustainable wild fishmeal in aquaculture, such products may reduce the feed availability of selenium, an essential element for aquatic animals. We believe that the findings of this study are relevant to the general field of commercial aquaculture. (C) 2016 Elsevier B.V. All rights reserved.