Dietary microencapsulated oil improves immune function and intestinal health in Nile tilapia fed with high-fat diet

Dietary usage of microencapsulated oils has been proved to promote growth and gut health in land animals, however, these beneficial effects have not been intensively investigated in aquatic animals. The present study hypothesized that dietary microencapsulated oils could alleviate negative effects caused by high-fat diet (HFD) in fish, thus we fed juvenile Nile tilapia with HFD (15% fat) by using normal or microencapsulated oils as lipid sources for 8 weeks. To compare the effects between different microencapsulated oils with different fatty acid composition, two oil mixtures (PL: 60% palm oil + 40% linseed oil; FL: 60% fish oil + 40% linseed oil) were used. After feeding trial, the growth, body composition, fatty acid composition, resistance to pathogenic bacteria challenge, activities of immune enzymes, expressions of inflammation genes, intestinal structure and microbiota were measured, respectively. The results indicated that microencapsulated oils didn't affect fish growth, body composition, and muscle fatty acid composition, but improved the intestinal activities of lysozyme (LZM) and resistance against Aeromonas hydrophila. Further tests showed that microencapsulated oils not only improved the structure of intestine, but also increased the number of beneficial bacteria (Bacillus and Paenibacillus) and decreased the number of harmful bacteria (Pseudoalteromonas and Roseovarius) in the intestine. Those beneficial effects are more significant between normal PL oil and microencapsulated PL oil, but no significant difference in FL oil groups. Taken together, these results suggested that microencapsulated oil might enhance immune activities in the Nile tilapia fed with HFD by improving intestinal structure and microflora. Moreover, the beneficial effects of the microencapsulated oil are correlated to the oil composition. To the best of our knowledge, this is the first study illustrating the beneficial effects of dietary microencapsulated oil in the fish fed with HFD.