Docosahexaenoic acid (DHA) and arachidonic acid (ARA) are essential to meet LC-PUFA requirements of juvenile California Yellowtail (Seriola dorsalis)

• Soybean oil can replace fish oil in California Yellowtail feeds, assuming adequate levels of DHA and ARA are provided.
• Dietary addition of ARA, EPA, and DHA may be valuable in terms of production performance and tissue fatty acid profiles.
• ARA and DHA appear to be the primary drivers of LC-PUFA essentiality for juvenile California Yellowtail.

It is likely that Seriola spp. have nutritional requirements for long-chain polyunsaturated fatty acids (LC-PUFAs) and are unable to meet physiological demand for these nutrients via biotransformation of C18 polyunsaturated fatty acids (C18 PUFAs). However, it is unclear whether 20:4n-6 (arachidonic acid, ARA), 20:5n-3 (eicosapentaenoic acid, EPA), and 22:6n-3 (docosahexaenoic acid, DHA) are each required or, as in other fish, EPA is comparatively unimportant in maintaining performance of Seriola spp. Accordingly, we assessed growth performance and tissue fatty acid composition of juvenile California Yellowtail Seriola dorsalis (formerly Seriola lalandi) fed a fish oil-based positive control diet (FISH), a soybean oil-based negative control diet (SOY), or experimental diets based on soybean oil supplemented with ARA, EPA, DHA, ARA and DHA, or all three of these fatty acids combined to achieve 50% or 100% of the concentrations typically observed in fish oil (SOY + 50% ARA, SOY + 100% ARA, SOY + 50% EPA, SOY + 100% EPA, SOY + 50% DHA, SOY + 100% DHA, SOY + 50% ARA and DHA, SOY + 100% ARA and DHA, SOY + 50% ALL, SOY + 100% ALL). As expected, fish fed the SOY diet exhibited significantly reduced growth relative to those fed the FISH diet. Supplementing with ARA alone had no effect on growth performance, and independent supplementation with EPA or DHA did not yield predictably positive effects on growth. However, fish fed the SOY + 100% ARA and DHA feed grew as well as those fed the FISH diet, and those raised on the SOY + 50% ALL and SOY + 100% ALL diets outperformed all others. Fatty acid composition of the fillet, liver, eye, and brain tissues was significantly affected by dietary treatment. As expected peripheral tissues were more modified than central tissues, and tissues of fish fed the soybean oil-based feeds exhibited higher levels of 18:2n-6 and lower levels of LC-PUFAs than those fed the rest of the experimental feeds. This effect was less overt among feeds supplemented with ARA and DHA or all three fatty acids. Results indicate that soybean oil can completely replace fish oil in California Yellowtail diets, assuming adequate levels of DHA and ARA are provided. Furthermore results illustrate the value of supplementing fish oil-free feeds with ARA, EPA, and DHA, but suggest that ARA and DHA are the primary drivers of LC-PUFA essentiality in this species.Statement of relevanceThe current manuscript provides valuable insights for fish nutritionists, for the aquafeed and aquaculture industries regarding fatty acid essentiality for marine carnivorous finfish. Our study supports the hypothesis that some LC-PUFAs are more physiologically important than others, with DHA and ARA being the primary drivers of fatty acid essentiality for juvenile California Yellowtail.