By Brett Glencross
Recently I was able to attend the 22nd International Symposium of Fish Nutrition and Feeding (ISFNF) in the beautiful tropical Australian city of Darwin. This event, coordinated every two years by the International Society for Aquaculture Nutrition (ISAN), presents the latest and greatest of the world’s aquaculture nutrition research in a four-day, single-session format.
What was interesting this year, in contrast to the past events of 2024 and 2022, was the focus of the majority of the ingredient studies. In previous years, the programme was flavoured by insects, single-cell proteins, algal- and GMO-oils. This time, it seems the focus of the scientific community is to reimagine a role for marine by-products, with talks from across the world discussing salmon by-product hydrolysates, catfish by-product meals and so on.
For decades, the aquaculture industry has battled a persistent, paradoxical critique: the reliance on wild-caught fish to feed farmed fish. Detractors have often seen the use of fishmeal as a fundamental flaw in the ‘blue revolution,’ arguing that we are merely robbing Peter to pay Paul due to the reliance on harvesting small pelagic species for feed. While agronomic innovations like insect meal, GMO oils and single-cell proteins offer interesting long-term prospects, they have persistently failed to deliver the promised tonnage the industry needs. However, it seems now that the tide is turning, as scientists begin to realise that we are routinely overlooking a colossal, immediate remedy resting right on our cutting boards: fishery and aquaculture by-products.
Every year, tens of millions of tonnes of fish heads, frames, skins and viscera are produced during seafood processing, often treated as expensive waste rather than an invaluable resource. We can already see from FAO and IFFO data that over 2.4 million tonnes of marine ingredients (meals and oils) are made from these resources each year, and this is growing at a rate of nearly 100,000 tonnes annually since 2020. Importantly, when properly reclaimed and rendered, these processing leftovers yield premium, highly digestible marine proteins and lipid profiles rich in omega-3 fatty acids. They provide the exact biological building blocks required by many of our farmed aquatic species, without adding a single ounce of additional fishing pressure to our oceans or requiring the mix of additives needed to make many other alternative ingredients work.
To build a truly circular blue economy, we must redefine our vocabulary. The heads, skins, and trimmings left behind are not ‘waste streams’—they are the nutritional foundation of the next generation of aquaculture feed. They are ‘side streams’: a valuable resource from which we can continue to make strategic ingredients for aquaculture’s future. The argument for integrating by-products into aquaculture feed extends far beyond simple resource conservation. It represents the operationalisation of a true circular economy. Transitioning to increased utilisation of by-product meals dramatically alters the carbon footprint of fish farming. It shifts the environmental burden of ingredient sourcing from primary extraction to upcycling, drastically lowering feed Scope 3 emissions that major retailers and carbon-conscious consumers now intensely scrutinise.
Admittedly, logistical obstacles remain. The nutritional profile of by-products can vary significantly based on species blend and freshness, demanding sophisticated supply chain tracking and rigorous quality control. Processing centres are often geographically fragmented, making cold-chain collection more challenging. However, these are engineering and logistical challenges, not biological dead-ends. Forward-thinking processors are already co-locating rendering facilities directly adjacent to filleting plants, preserving nutritional integrity and proving that localised circular loops are highly profitable.
To fully unlock this resource, we require an ideological shift across the entire seafood supply chain. Certification programmes must continue to reward feeds derived from responsibly managed by-products, and consumer brands must proactively market the ecological triumph of upcycled marine ingredients. We can no longer afford the luxury of linear thinking in food production. By systematically reclaiming the hidden bounty of our seafood processing lines, we can all see an aquaculture future that is not just reimagining its feed resources, but has found that the tide has turned, and we are reintroducing marine ingredients back into diets.
