---
title: "Omega-3 byproduct oil could fully replace fish oil in European seabass feeds, study finds"
summary: "A peer-reviewed study by researchers from the University of Porto, CIIMAR, and the University of Florence, in collaboration with EPAX®, found that fatty acid ethyl ester (FAEE) oil — a byproduct of omega-3 supplement production — can completely replace fish oil in juvenile European seabass diets without impairing growth, feed utilization, or nutrient digestibility. However, the substitution significantly reduced muscle DHA levels, pointing to a potential nutritional quality trade-off that may require mitigation."
url: "https://feedsoft.ai/articles/omega-3-byproduct-oil-could-fully-replace-fish-oil-in-european-seabass-feeds-study-finds-cde68805"
publisher: "The Feed Report"
section: "Aquafeed"
author: "The Feed Desk"
datePublished: "2026-10-01T01:49:32.363Z"
dateModified: "2026-10-01T01:49:32.363Z"
sources:
  - title: "Omega-3 byproduct shows potential to replace fish oil in seabass feeds"
    url: "https://www.aquafeed.com/newsroom/news/omega-3-byproduct-shows-potential-to-replace-fish-oil-in-seabass-feeds/"
---

# Omega-3 byproduct oil could fully replace fish oil in European seabass feeds, study finds

*A peer-reviewed study by researchers from the University of Porto, CIIMAR, and the University of Florence, in collaboration with EPAX®, found that fatty acid ethyl ester (FAEE) oil — a byproduct of omega-3 supplement production — can completely replace fish oil in juvenile European seabass diets without impairing growth, feed utilization, or nutrient digestibility. However, the substitution significantly reduced muscle DHA levels, pointing to a potential nutritional quality trade-off that may require mitigation.*

Researchers have found that fatty acid ethyl ester (FAEE) oil, a byproduct generated during the production of omega-3 supplements, can fully replace fish oil in feeds for juvenile European seabass (*Dicentrarchus labrax*) without negatively affecting growth or feed efficiency, according to a study published in the journal *Aquaculture*.

The research was conducted by scientists from the University of Porto, CIIMAR, and the University of Florence, together with the Norwegian company EPAX®, and was funded by the Portuguese Foundation for Science and Technology (FCT). The peer-reviewed paper is scheduled for publication in the January 2027 issue of *Aquaculture*.

## Background and rationale

Fish oil is widely used in aquafeeds for its high EPA and DHA content, but the source faces well-documented constraints. According to the study as reported by Aquafeed.com, "limited supply, high cost, and environmental impacts have driven interest in alternative lipid sources." FAEE oil arises as a co-product of omega-3 concentrate manufacturing: the source notes that "approximately 70% of the original fish oil can be discarded as FAEE oil" during processing, making it a potentially abundant and low-cost material.

Unlike conventional fish and vegetable oils, which consist predominantly of triacylglycerols (TAGs), FAEE oil is composed primarily of ethyl esters (EEs). The source notes that "its metabolic utilization in fish remains relatively understudied."

## Experimental design

The team formulated four isoproteic and isolipidic diets containing approximately 48% crude protein and 16% crude lipid, with varying proportions of fish oil, rapeseed oil, and FAEE oil. In the highest FAEE treatment, fish oil was completely replaced by FAEE oil, which accounted for 10.8% of the complete diet. The FAEE oil used in the trial was supplied by Epax® Norway AS, Ålesund, Norway, and contained 3.9% EPA and 0.3% DHA.

A total of 180 juvenile European seabass with an initial weight of approximately 62 g were fed the experimental diets for 88 days. A separate digestibility trial was conducted to assess the apparent digestibility of dry matter, protein, lipid, and energy.

## Growth and digestibility unaffected

The study found that FAEE oil "had no significant effect on growth performance, feed intake, feed efficiency, survival, or nutrient and energy retention." Whole-body composition and organ indices were also unaffected. Apparent digestibility coefficients for dry matter, protein, lipid, and energy "did not differ significantly among diets," and intestinal enzyme activities remained similar across treatments.

The authors noted that a previous literature body has documented "species-specific responses to FAEE," with "reduced performance reported at some inclusion levels in red drum and rainbow trout," while the present study used FAEE at up to 10.8% of the diet without adverse growth effects. They also suggested that a trial temperature of 23°C may have contributed to the similar lipid digestibility observed across diets.

## Muscle DHA declined sharply

Despite the positive growth results, dietary lipid source significantly altered muscle fatty acid composition. DHA in muscle tissue dropped from 11.13% of total muscle fatty acids in the control group to 3.80% at the highest FAEE inclusion. Combined muscle EPA + DHA content fell from 16.11% in the control diet to 8.57% in the highest-FAEE treatment.

As dietary DHA decreased with rising FAEE inclusion, the highest FAEE diet also showed "the highest saturated fatty acid concentration," which was associated with higher atherogenicity and thrombogenicity indices in muscle, though the source notes "both remained below the limits cited in the study." Muscle EPA levels were maintained between the control and highest-FAEE groups despite lower dietary EPA in the latter, which the authors attributed to the known capacity of fish to selectively retain EPA and DHA when dietary levels are low.

## Implications for feed formulation

Replacing fish oil with FAEE in the study reduced dietary EPA + DHA from 2.04% of the diet in the control to 0.59% in the highest FAEE treatment, described by the source as "slightly below previously reported minimum n-3 LC-PUFA recommendations for juvenile European seabass." Despite this, growth and feed utilization were maintained, leading the authors to suggest that "the dietary n-3 LC-PUFA requirements of juvenile European seabass may be lower than previously estimated and warrant reevaluation."

The researchers cautioned, however, that "the reduction in muscle DHA at high FAEE inclusion suggests that DHA supplementation may be needed to maintain the nutritional quality of the final product." The findings highlight the potential to valorize a byproduct of omega-3 processing as an alternative lipid source in seabass aquafeeds, with the caveat that end-product fatty acid quality requires further attention.

*Reference: Xu, Y., Vieira, L., Pulido-Rodríguez, L., Parisi, G., Oliva-Teles, A., Peres, H., & Magalhães, R. (2027). Fatty acid ethyl esters as an alternative oil in aquafeeds: Effects on growth performance and nutrient digestibility in European seabass juveniles. Aquaculture, 627 (January 2027), 744506. https://doi.org/10.1016/j.aquaculture.2026.744506*

## Sources

- [Omega-3 byproduct shows potential to replace fish oil in seabass feeds](https://www.aquafeed.com/newsroom/news/omega-3-byproduct-shows-potential-to-replace-fish-oil-in-seabass-feeds/)

*Cite as: The Feed Report, "Omega-3 byproduct oil could fully replace fish oil in European seabass feeds, study finds", https://feedsoft.ai/articles/omega-3-byproduct-oil-could-fully-replace-fish-oil-in-european-seabass-feeds-study-finds-cde68805 (as of 2026-10-01).*