Researchers at the Institute of Aquaculture -- part of Scotland's University of Stirling -- have developed a new metric to aid the improvement of omega-3 and nutrient retention in farmed fish.

Existing and widely used fish-in, fish-out (FIFO) metrics measure the biomass of wild fish used to produce farmed fish but fail to account for nutrient retention, the researchers -- in collaboration with the universities of Lancaster, Aberdeen, and Cambridge -- noted.

Their new "nutrient FIFO (nFIFO)" builds on the previous FIFO metric but includes the important aspect of nutrient retention. It also takes by-products into account -- which are not edible to humans but can be a sustainable resource for producing marine ingredients to be used in aquaculture.

Aquaculture's reliance on wild-caught fish for feed, particularly fishmeal and fish oil, has raised sustainability concerns. The study found that farmed salmon are only 38% efficient in converting omega-3 inputs into final nutrients. However, using fishery by-products as feed could dramatically improve nutrient retention, supporting a more sustainable aquaculture system, said Stirling.

The research team has also developed a calculation tool to help the industry adopt the nFIFO metric, which is available through Blue Food Performance's sustainability platform.

"Unlike traditional approaches, this new nFIFO metric accounts for the retention of key nutrients in the final farmed fish, providing a more targeted means of measuring and improving aquaculture's resource efficiency," said Richard Newton, lead author of the study.

"This shift highlights the ever more important role of by-products in transforming marine resources into valuable nutrition within the aquaculture sector," he added.