FISH OIL AND ALTERNATIVE OIL SOURCES-BASED DIETS SUPPLEMENTED WITH OX-BILE: EFFECTS ON GROWTH, NUTRIENTS DIGESTIBILITY, BODY COMPOSITION AND INTESTINAL BILE SALT CONCENTRATION IN RAINBOW TROUT Oncorhynchus mykiss

Limited availability of fish oil has increased attention to other fat sources such as terrestrial plant oil and its byproducts. The inclusion of such ingredients may cause poor fat digestibility in fish due to a large content of saturated fatty acids. Furthermore, vegetable oils have low levels of bile salt precursors which may have a negative impact on bile metabolism. An emulsifier such as ox-bile may enhance the utilization of low digestible oil. Therefore, the present study aims to evaluate the potential of bile addition to fat metabolism when fish were fed with fish oil and alternative-based oil-sources. Nine isonitrogenous (44%, fish meal based) and iso-lipidic (20%) diets with a 3 × 3 factorial design were formulated to contain three levels of ox-bile (0, 1, 3%) and three sources of oil (fish oil, soybean oil, and fat powder). Juvenile rainbow trout (initial weight of 24.4 g) were fed to apparent satiation twice daily for nine weeks.

Results of growth performance parameters of fish were not affected (p>0.05) by the factors of ox-bile and/or oil source. However, fat powder-based diets fed groups resulted in lower (p < 0.05) fat and protein digestibility (p < 0.05), concurrently decreased whole-body fat and increased the protein compared to fish and soybean oil-based diets whereas supplementation of ox-bile did not affect fat digestibly. Both oil source and ox-bile addition affected the bile concentration of proximal and distal intestine (p<0.05). The fish oil diet led to a lower bile content in both proximal and distal intestine (p<0.05). Histology of liver showed that leukocyte infiltration and enlarged bile ducts in fat powder fed group whereas bile supplementation exhibited some necrotic cells. In conclusion, dietary ox-bile may not be an effective way to improve fat powder digestibility.