Regulation of the omega-3 fatty acid biosynthetic pathway and fatty acids bioconversion capacity in selected rainbow trout (Oncorhynchus mykiss) using alternative dietary oils

Authors: KAJBAF, KIMIA - University Of Idaho; Overturf, Kenneth; Cleveland, Beth; KUMAR, VIKAS - University Of Idaho

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2025
Publication Date: 1/17/2025
Citation: Kajbaf, K., Overturf, K.E., Cleveland, B.M., Kumar, V. 2025. Regulation of the omega-3 fatty acid biosynthetic pathway and fatty acids bioconversion capacity in selected rainbow trout (Oncorhynchus mykiss) using alternative dietary oils. Animal Feed Science and Technology. https://doi.org/10.1016/j.anifeedsci.2025.116219.
DOI: https://doi.org/10.1016/j.anifeedsci.2025.116219

Interpretive Summary: Aquaculture is currently the fastest growing sector of animal agriculture. Of primary concern in aquaculture is the current reliance on limited protein and oil sources, mainly fishmeal(FM) and fish oil (FO), with FO the main limiting factor in aquaculture feeds. Although FO is the ideal energy source for fish, as it provides all the essential fatty acids and benefits the final quality of the final product, namely with increased levels of fatty acids known to improve human heart and brain health. Previous studies have shown that fish can grow on diets formulated with oils from other sources, but this is also reflected in the fatty acid profile of the final product which has reduced health benefits related to changes in the fatty acid profile. Certain fish species are capable of converting other oil sources into the healthy omega-3 fatty acids, therefore this study was to test the effect of other dietary oil sources in rainbow trout. During the study six experimental diets were formulated containing oil from fish oil and alternative oil sources such as linseed, soy, canola, coriander and algae. Groups of rainbow trout were fed the diets for 10 weeks and then evaluated for growth, fatty acid muscle content, and the expression of genes related to lipid biosynthesis and antioxidation. The findings from this study showed that fish on the algae oil replacement diet grew the best and had the highest omega-3 fatty acid levels when compared to the alternative oil diets along with higher expression levels for genes related to lipid biosynthesis. The expression of antioxidant genes was generally higher in fish on the alternative diets suggesting that alternative oils might provide protection from oxidative stress. These findings suggest that fish oil can be substantially replaced in aquaculture diets with alternative sustainable oils and maintain good growth, healthy levels of omega-3 fatty acids, and improve antioxidant potential.

Technical Abstract: Currently, vegetable oils (VO) have become the primary alternative for fish oil (FO), as they are readily available, cost effective ingredients that contain high levels of essential C18 fatty acids (FA). Through a selective breeding program we have developed rainbow trout (Oncorhynchus mykiss) families which are improved in their ability to desaturate and elongate a-linolenic acid (18:3n-3; ALA) to produce the n-3 long-chain polyunsaturated fatty acids [LC-PUFA, eicosapentaenoic acid (20:5n-3; EPA), docosahexaenoic acid (22:6n-3; DHA)]. Therefore, we investigated the influence of fish oil (FO) and alternative oil sources [linseed (LO), soy (SO), canola (CO), coriander (CNO) and algae (AO), all of which include various levels of ALA, linoleic acid, oleic acid, and DHA FAs] on growth, muscle tissue FA composition, and lipid-related hepatic gene expression in trout. Six experimental diets (D1: 12%FO, D2: 12%LO, D3: 6% LO+2%SO+2%CO+2%CNO, D4:3%SO+3%CO+6%CNO, D5: 6%LO+6%AO and D6: 12%AO) were formulated and fed in triplicate to selected trout (initial average weight 470 ' 30 g fish- 1) for 10 weeks. Highest weight gain % was observed in AO fed group (D6) whereas lowest value was found in D4. Total saturated FA in muscle was affected by oil sources; diets with LO, SO, CO and CNO exhibited lower deposition than other oil sources. Among VO sources, highest EPA deposition was found in D5 (AO+LO; 1.74%) and was similar to D2 (LO; 1.61%), whereas lowest value in D4 (1.26%) which was similar to D3 (1.45%). Highest and lowest muscle content of PUFAs was observed in D2 and D4 respectively. Total EPA and DHA content were highest in D6 which is almost three times higher than D2 fed group. The highest expression levels of PPARG, SRBP2 and FADS6 was observed in D2. FAS had the highest relative expression in D1 and the lowest in D3 and D5 where both included 50% linseed oil and 50% alternative oil. Regarding the antioxidant properties of these diets, replacement of fish oil with linseed oil (D2) increased the expression of CAT and GST significantly. Conclusively, algae oil can be used as an alternative source of oil to enhance the growth and increase the deposition of EPA and DHA in salmonid fillet for healthy food.