Effects of canola meal on growth, feed utilisation, plasma biochemistry, histology of digestive organs and hepatic gene expression of barramundi (Asian seabass; Lates calcarifer)

Abstract

The serial replacement of fish meal (anchovetta) by canola meal (CM) (100, 200, 300 g kg−1 as either solvent extracted (SE) CM or expeller extracted (EX) CM was undertaken to investigate the effects of increasing dietary CM levels on feed intake, growth, protein and energy retention, plasma biochemistry and the expression of a suite of hepatic genes in barramundi (Asian seabass; Lates calcarifer) over an eight week feeding trial. An additional diet using lupin kernel meal (LM) to replace the fish meal was also included as a comparative reference. Eight iso-digestible nitrogenous (423±29 g kg−1) and iso-digestible energetic (14.6±8 MJ kg−1 DM) diets were formulated. Each diet was randomly allocated to triplicate groups of fish in seawater tanks (600 L), and each tank was stocked with 15 fish (53.4±7.0 g). Fish were fed once daily (9:00–10:00) to apparent satiation, and uneaten feed was collected to determine feed consumption. The results showed that the survival, feed intake, growth, FCR, energy and protein retention of fish fed the diet containing SE CM were similar or even higher to those of fish fed the fish meal reference diet (FM) and the LM diet. Fish fed with the diet containing 300 g kg−1 SE CM did not show any changes in biochemistry and gene expression in a suite of detoxification genes. However, the diet with 300g kg−1 EX CM depressed feed intake, growth performance and increased feed conversion ratio (FCR). Transcription of genes involving in fatty acid synthesis and the TCA cycle were not changed by different diets. The down regulation of gene expression in certain detoxification genes (Lc CYP1A1, Lc CYP3A, Lc CYP2N and Lc GST) was observed in fish fed with the diet containing 300 g kg−1 EX CM compared to the FM control diet and other experimental diets. In general, the SE CM can be used up to 300 g kg−1 diet without negative performance effects or signs of clinical plasma biochemistry. By contrast the maximum acceptable level of the EX CM for barramundi was only 200 g kg−1. Higher inclusion level of the EX CM induced negative effects on growth performance, feed utilisation, plasma biochemistry and gene expression in relation to detoxification.