Evaluation of enzyme- and Rhizopus oligosporus-treated high oil residue camelina meal on rainbow trout growth performance and distal intestine histology and inflammatory biomarker gene expression

Abstract

The effect of high oil residue camelina meal (HORM) and treated HORM on rainbow trout growth performance and related parameters was determined. Two isocaloric, isonitrogenous diets containing fish meal at a level of 100g/kg and fish oil at a level of 50g/kg were formulated. One was a control diet, and the other contained HORM at an 80g/kg inclusion level. In an additional five test diets, HORM was replaced with treated HORM (water-soaked HORM, pectinase HORM, Superzyme HORM, High-Pectinase Superzyme HORM (HP-SZ HORM) or Rhizopus HORM/wheat (1:3 wheat:HORM fermented with R. oligosporus; R-HORM). Test ingredients in treated HORM diets were mixed with water and/or their respective enzymes, then incubated for 24h at 40°C or fermented by R. oligosporus fungus for 72h. Diets were fed to rainbow trout (average weight: 33.7g; 30 fish/126L tank; 3 tanks/treatment) in a freshwater (11.8±0.7°C), flow-through system for 112days. Treatment of HORM with water or enzyme provided intermediate growth between the control and R-HORM diets and the initial four weeks on test. On day 28, fish fed the control diet had a higher specific growth rate (SGR) than fish fed HORM and R-HORM and a higher thermal growth coefficient than fish fed R-HORM (P<0.05). On day 56, control-fed fish had a significantly higher weight gain and fork length than water-soaked HORM- and R-HORM -fed fish. On day 112, fish fed the control diet had a higher SGR than fish fed R-HORM and fish fed all diets except water-soaked HORM had a longer fork length (P<0.05) than fish fed R-HORM (P<0.05). There were no significant differences in the transcript levels of eight inflammatory biomarker genes (GILTa, GILTb, PAR2a, PAR2b, IL1ß3, MyD88, TGFß1a and TGFß1b) in the distal intestines of fish fed the HORM, HP-SZ HORM or R-HORM diets, compared with fish fed the control diet. An inclusion level of 80g/kg HORM and water- and enzyme-treated HORM (all three treatments) are acceptable in juvenile rainbow trout diets. Future studies may involve similar treatments at higher dietary inclusion levels and HORM fermented with R. oligosporus using a substrate other than wheat.