Bile acid supplementation in alternative lipid-based diets: Effects on growth, histopathology and digestibility in rainbow trout (Oncorhynchus mykiss)

Authors: AMIRKOLAEI, ABDOLSAMAD - University Of Idaho; BENITO, MARINA - University Of Idaho; KUMAR, VIKAS - University Of Idaho; Romano, Nicholas; HONG, JEONGWHUI - University Of Idaho; SMALL, BRIAN - University Of Idaho

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2024
Publication Date: 12/9/2024
Citation: Amirkolaei, A.K., Benito, M.M., Kumar, V., Romano, N.P., Hong, J., Small, B.C. Bile acid supplementation in alternative lipid-based diets: Effects on growth, histopathology and digestibility in rainbow trout (Oncorhynchus mykiss). Animal Feed Science and Technology. 319:0377-8401. 2024. https://doi.org/10.1016/j.anifeedsci.2024.116179.
DOI: https://doi.org/10.1016/j.anifeedsci.2024.116179

Interpretive Summary: Fish oil is becoming more expensive and less available as an ingredient in fish feeds. Thus, feed manufacturers are increasingly relying on fish oil alternatives, such as plant oils. Plant oils may not be as digestible in fish, but digestibility could potentially be improved by adding bile acid in the diets. This is because bile acid physically breaks up oils into smaller particles when ingested by fish. In this feeding trial, rainbow trout were fed diets with three different lipid sources (fish oil, soybean oil and palm fat powder) with or without supplementations of bile (0, 1, or 3%). It was indeed found that bile acid improved lipid digestibility in rainbow trout, although growth was unaffected. Caution should be used when including bile acid in aquafeeds, particularly when using fish oil, due to observations of abnormalities in the liver. However, when using fish oil alternatives, the inclusion of 1% bile acid can be beneficial to rainbow trout.

Technical Abstract: Fish oil alternatives, such as terrestrial plant oil and its byproducts, may cause poor lipid digestibility in fish due to a large content of saturated fatty acids. Reduced lipid digestibility is assumed to be caused, in part, by hindering bile acid metabolism and thus decreasing emulsification capacity. This study aims to evaluate the potential of dietary bile acid additions to the growth, lipid digestibility, intestinal bile acid levels and liver/intestinal histopathology of rainbow trout, Oncorhynchus mykiss, when using different lipid sources. In a 3 × 3 factorial design, nine iso-lipidic diets were formulated to contain three levels of ox-bile (0, 1 and 3 %) and three lipid sources (fish oil, soybean oil, and palm fat powder). Fish (initial weight of 24.4 ± 1.55 g) were fed to apparent satiation twice daily for nine weeks. Results showed that growth was unaffected by ox-bile and/or lipid source (p > 0.05). However, exchanging fat powder for fish oil or soybean oil resulted in lower dietary lipid and protein digestibility (p < 0.05). Ox-bile significantly improved lipid digestibility (57.3 versus 50 %) in fish fed the fat powder diet (p < 0.05). The fat powder diet significantly decreased whole-body lipid and increased whole-body protein, compared to those fed the fish oil or soybean oil diets (p < 0.05). Both lipid source and ox-bile addition affected the bile acid concentration of proximal and distal intestine (p < 0.05). The fish oil diet led to a lower bile content in distal intestine and tendency toward a lower bile content in proximal intestine (p < 0.05). The fat powder diet caused bile duct enlargement and inflammation in the liver but was mitigated by 1 % ox-bile. In contrast, the livers of trout fed fish oil with 1 or 3 % ox-bile showed inflammation and in some cases necrosis. In conclusion, dietary ox-bile significantly improved lipid digestibility in fat powder-based diets as well as reduced hepatic inflammation. However, inclusions of ox-bile at 3 % in the fish or soybean oil-based diets appeared to show a cytotoxic effect.