Effects of dietary arachidonic acid supplementation in low fishmeal and fish oil-free diets on growth performance, inflammatory response, gut histology, and non-specific immunity in sub-adult rainbow trout, Oncorhynchus mykis

Authors: HONG, J. - University Of Idaho; ORTIZ, J. - University Of Idaho; Sealey, Wendy; SMALL, B. - University Of Idaho

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2023
Publication Date: 10/30/2023
Citation: Hong, J., Ortiz, J.G., Sealey, W.M., Small, B.C. 2023. Effects of dietary arachidonic acid supplementation in low fishmeal and fish oil-free diets on growth performance, inflammatory response, gut histology, and non-specific immunity in sub-adult rainbow trout, Oncorhynchus mykis. Aquaculture. 740272. https://doi.org/10.1016/j.aquaculture.2023.740272.
DOI: https://doi.org/10.1016/j.aquaculture.2023.740272

Interpretive Summary: Arachidonic acid is a long-chain fatty acid and plays a wide range of physiological roles. Significant reductions in fishmeal and fish oil, the primary sources of arachidonic acid, in aquafeeds, could limit the ability of rainbow trout feeds to provide adequate dietary amounts to support growth and immune function. USDA ARS nutritionist collaborated with University of Idaho, Hagerman Fish Culture Experiment Station researchers to investigate the effects of different levels of dietary arachidonic acid on the growth performance and immune response of rainbow trout. Results from the study identified what arachidonic acid supplementation levels are needed in low fishmeal and fish oil-free diets to maintain rainbow trout immune function. These data help trout producers and feed formulators develop improved plant-based feed formulations that maintain production efficiency while decreasing dependency on limited marine ingredient resources.

Technical Abstract: Arachidonic acid (ARA) is becoming increasingly important due to significant reductions in fishmeal and fish oil, the primary sources of ARA, in aquafeeds. ARA is an essential omega-6 fatty acid in some fish species and plays a wide range of physiological roles. However, studies reported to date have demonstrated contrasting findings concerning the effects of ARA in fish growth and health, regardless of the fish’s trophic level. Therefore, a study was conducted to evaluate the effects of different levels of ARA on growth performance, the fatty acid composition of whole-body and ovary, intestinal inflammatory gene expression, gut histology, antioxidant activity, and non-specific immunity in rainbow trout (Oncorhynchus mykiss) during final grow-out. Four isonitrogenous (51% crude protein), isolipidic (15% crude lipid), and isocaloric (23 MJ/kg) diets were formulated and supplemented with ARA-enriched oil (40%), resulting in analyzed ARA levels of 0.10 (ARA0.10), 3.95 (ARA3.95), 7.67 ARA(7.67), and 14.8% (ARA14.8) of total fatty acid, respectively. Rainbow trout (307 ± 3.64 g) were fed to apparent satiation three times a day for 12 weeks to assess growth performance, feed utilization, and intestinal inflammatory response. The fish were then exposed to acute stress to evaluate circulating cortisol, prostaglandin E2, antioxidant activity, and non-specific immune response. The 12-week growth trial demonstrated that dietary ARA did not affect rainbow trout growth performance and feed utilization during the final grow-out. Whole-body fatty acid profiles reflected those of the diets except for eicosapentaenoic acid (EPA) content being significantly lower in the ARA14.8 group than in the ARA0.10 and ARA3.95 groups. EPA and docosahexaenoic acid (DHA) contents in the ovary were less affected by dietary ARA supplementation, likely reflecting the selective deposition of those fatty acids in embryonic development. The expression of tnf-a was significantly downregulated in ARA7.67 and ARA14.8 groups relative to other treatment groups, and only distal intestinal villus height was significantly increased in the ARA3.95 group, suggesting that dietary ARA supported intestinal health. Plasma superoxide dismutase, catalase, and lysozyme activity significantly increased in both pre-and post-stress groups due to incremental increases in dietary ARA. These results suggest that supplementation of ARA in low fishmeal and fish oil-free, finishing diet enhances innate immune function and antioxidant responses while supporting intestinal health in sub-adult rainbow trout.