Severity of soybean meal induced distal intestinal inflammation, enterocyte proliferation rate, and fatty acid binding protein (Fabp2) level differ between strains of rainbow trout (Oncorhynchus mykiss)

Abstract

Complete replacement of fishmeal in feeds for carnivorous fishes often causes reduced growth and can negatively affect gut health. Little is known about strain differences regarding effects of plant based diets in fish and the potential for selection for improved gut health and performance on an all plant diet. The current study investigated the response of a non-selected (NS) and selected (SE) strain of rainbow trout to a fishmeal free, plant based diet containing a high level of soybean meal. Fish from both strains, about 5g at start in fresh water, were fed either a fish meal based control diet without soybean meal (FM) or an all plant meal diet (PM) containing 19% soybean meal, i.e. in four treatments: FM-NS, FM-SE, PM-NS, and PM-SE. Feed intake was monitored and growth was recorded at 60days of feeding. Tissue samples of the distal intestine (DI) were collected for histological examinations and for evaluation of intestinal cell proliferation and presence of intestinal fatty acid binding protein, Fabp2. The results showed significantly better growth rate and feed conversion ratio in the SE strain, but only for fish fed the PM diet. Fish fed the FM diet showed no significant strain difference. Better feed conversion was also observed for the SE strain compared to the NS strain, independent of diet. A strain difference was also observed for degree of soybean meal induced inflammation. Fish from the PM-NS treatment showed typical signs of DI inflammation, while the PM-SE fish appeared normal and quite similar to FM fed fish. Fish from the SE strain in general showed lower intestinal cell proliferation compared to the NS fish, and no effect of diet, whereas in NS fish fed the PM diet proliferation was 65% higher. The results regarding Fabp2 indicated a similar picture for fatty acid transport. Results of the current work showed that sensitivity to dietary soybean meal varies between rainbow trout strains, and strongly suggests that improvement in tolerance may be achieved by selective breeding on a diet containing soybean meal. Moreover, tools for the study of Fabp2 were developed.