Farmed fish eat compressed pellets made primarily from plant proteins, with smaller amounts of fishmeal, fish oil, and a long list of vitamins, minerals, and other additives. The exact recipe varies by species, but modern aquaculture feed looks very different from what most people imagine. For Atlantic salmon, one of the most widely farmed fish in the world, fishmeal and fish oil now make up less than 10% of the diet. The rest comes from terrestrial crops, animal byproducts, and synthetic supplements.
The Base: Plant Proteins and Grains
The bulk of commercial fish feed is built from the same crops that feed livestock on land. Soybean meal is the most common plant protein, typically making up 15 to 20% of the diet. Wheat flour serves as both a carbohydrate source and a binding agent that holds pellets together, usually around 19 to 21% of the formula. Corn protein concentrate, canola meal, and pea protein round out the plant side, each contributing additional amino acids and energy.
These plant ingredients are cost-effective and available year-round, which is why the industry has shifted so heavily toward them over the past two decades. The tradeoff is that plant proteins don’t perfectly match the amino acid profile that carnivorous fish like salmon need, so feed manufacturers compensate by adding synthetic amino acids like lysine, methionine, and taurine to fill the gaps.
Fishmeal and Fish Oil
Fishmeal is made by cooking, pressing, and drying whole fish, usually small oily species like anchovies, menhaden, and herring. Anchovy meal is about 64% protein, menhaden meal around 60%, and herring meal roughly 70%. Fish oil, extracted during the same process, provides the omega-3 fatty acids (EPA and DHA) that make seafood nutritionally valuable.
Historically, fishmeal and fish oil were the dominant ingredients in salmon feed. That’s no longer the case. Inclusion rates have dropped dramatically as plant-based and alternative ingredients have improved. This shift matters because it determines how many wild fish are needed to produce each kilogram of farmed fish. Norway’s entire salmon sector used over 2.1 million tonnes of whole wild fish in 2020 to produce the fishmeal and fish oil in its feeds, a number the industry is actively trying to reduce.
Animal Byproducts
Fish feed also contains processed leftovers from other animal industries. Meat and bone meal, which is about 50% protein, comes from livestock rendering. Poultry byproduct meal and hydrolyzed feather meal (80 to 85% protein) are common additions. Spray-dried blood meal, at roughly 85% protein, is one of the most concentrated protein sources available. These ingredients are cheap and protein-dense, making them useful for hitting the high protein targets that carnivorous fish require without relying entirely on fishmeal.
Mill byproducts fill out the formula further. Wheat bran, wheat germ meal, corn gluten feed, and distillers dried grains (a byproduct of ethanol production) all contribute varying levels of protein, fat, and fiber. None of these are star ingredients on their own, but together they form the carbohydrate and fiber backbone of many commercial feeds.
Newer Alternatives: Insects and Algae
Black soldier fly larvae meal is one of the most promising new protein sources in aquaculture. Trials with Atlantic salmon have replaced up to 100% of the fishmeal with insect meal in tank experiments, and commercial farms are already using it at 5 to 10% inclusion rates. At around 15% of total dietary protein, insect meal can substitute for roughly a third of the fishmeal protein in a salmon diet with no measurable drop in growth or welfare. The larvae are raised on organic waste streams, which gives them a strong sustainability profile compared to both fishmeal and soy.
Algae oil is tackling the fish oil side of the equation. A recent study fully replaced fish oil with oil from a microalgae species called Schizochytrium in Atlantic salmon feed and found no negative effects on growth, feed intake, gut health, pigmentation, or fillet quality. The salmon actually ended up with higher DHA concentrations in their flesh, which is a direct nutritional benefit for consumers. Perhaps more striking, the algae-fed fish had 70 to 79% lower levels of certain environmental contaminants (dioxins and dioxin-like compounds) in their fillets, since those pollutants accumulate in marine food chains and concentrate in fish oil.
Why Farmed Salmon Is Pink
Wild salmon get their pink-to-red color from eating krill and shrimp, which are rich in a pigment called astaxanthin. Farmed salmon don’t eat krill, so without supplementation their flesh would be gray. Feed manufacturers add synthetic or naturally derived astaxanthin to the pellets at doses of 50 to 100 milligrams per kilogram of feed. This single additive is surprisingly expensive, accounting for 15 to 20% of total feed cost and 6 to 8% of the entire cost of producing a farmed salmon. The color intensifies as the fish grows larger and as dietary pigment levels increase, so producers carefully adjust concentrations throughout the grow-out period to hit the target color at harvest.
Vitamins, Minerals, and Gut Health Additives
Beyond the main macronutrients, every commercial feed contains a premix of micronutrients. Vitamin C is added at 100 to 300 milligrams per kilogram for immune function and stress resistance. Choline chloride and betaine, each dosed at 500 to 1,000 milligrams per kilogram, support growth and help fish cope with changes in salinity. Essential minerals like manganese are calibrated carefully, though insect-based feeds may naturally supply enough to reduce the need for supplementation.
Probiotics and prebiotics are increasingly common. Probiotics (live beneficial bacteria) are added at concentrations ranging from tens of thousands to a billion colony-forming units per gram of feed. Prebiotics, which are indigestible fibers that feed beneficial gut bacteria, are typically included at 2 to 10 grams per kilogram. Common prebiotics include inulin, fructooligosaccharides, and beta-glucans. These additives aim to improve digestion, strengthen immunity, and reduce the need for antibiotics. Plant-derived essential oils with antimicrobial properties are also widely used.
Floating vs. Sinking Pellets
Feed comes in two main physical forms, and the choice depends on the species and water temperature. Floating pellets are made through extrusion, a process that uses high pressure, heat, and friction to cook and expand the ingredients. The result is a buoyant pellet that stays on the surface, letting farmers watch their fish eat and gauge appetite in real time. Sinking pellets are made with a simpler steam-pelleting process and are used for bottom-feeding species or during cooler water temperatures when fish feed at lower depths. Catfish farms, for example, switch to sinking feed in cold weather. Extruded floating feeds cost more to produce because of the extra energy involved and some nutrient loss during processing, but the ability to monitor feeding behavior makes them the default for most species.