Vol. XIX · Fish and Seafood Plate 8 of 9sustainable seafood, overfishing, aquaculture, farmed fish, fish farming, MSC, ASC, fishmeal, fish in fish out, mussels, sardines, bycatch, FAOTF

Choosing Responsibly.

A farmed salmon eats wild fish, through its feed. A farmed mussel eats nothing anyone has to catch, and cleans the water as it grows.

The FAO assesses the world's marine fish stocks every two years. In 1974, nine-tenths were fished within biologically sustainable levels; by 2021 the share had fallen to about 62 %, so more than a third are overfished. Some fisheries have recovered under good management; many have not. Meanwhile aquaculture has grown so fast that in 2022 it produced, for the first time, more aquatic animals than wild capture. Farming takes pressure off wild stocks only if the farmed animals do not eat too much wild fish themselves.

That depends on the species. Carnivorous fish such as salmon and prawns are fed pellets that once were mostly fishmeal and fish oil; plant proteins and oils now replace much of it, and the "fish in, fish out" ratio for farmed salmon has fallen to around one. Carp and tilapia need little or no fishmeal. Mussels, oysters and clams are fed by the sea and filter it as they grow. Labels help: MSC for wild fisheries independently certified as sustainable, ASC and similar schemes for responsible farms. The workshop works out how much wild fish goes into a farmed one.

Below: the kilograms of wild fish used to feed one kilogram of farmed fish, from the feed conversion and the share of marine ingredients you choose (the IFFO "fish in : fish out" method), and the FAO's share of stocks fished sustainably in 1974 and 2021.

What you will learn
Workshop
Fish in : fish out = feed conversion ratio × share of fishmeal and fish oil in the feed ÷ 0.275 (about 22.5 % fishmeal and 5 % fish oil from whole fish, the IFFO yields); a teaching calculator that ignores by-product trimmings. Stock figures: FAO, The State of World Fisheries and Aquaculture 2024.

Eat lower on the chain, read the label

With 1.25 kg of feed per kilogram of fish and a quarter of it from fishmeal and oil, about 1.14 kg of wild fish go into each kilogram of farmed salmon; with a 1990s-style feed of 60 % marine ingredients it was about 2.8 kg; a carp fed mostly on plants uses about 0.17 kg. Modern published figures for salmon are near one, and lower when trimmings from fish processing are counted. The wild fish used — anchovies, sardines, sand eels — are themselves food for people and seabirds, so the ratio matters.

Practical choices. Eat a variety rather than the same few species (salmon, tuna, prawns). Prefer small, fast-breeding fish (sardines, mackerel, herring, anchovies), farmed bivalves (mussels, oysters, clams) and herbivorous farmed fish (carp, tilapia). Look for MSC on wild fish and ASC or equivalent on farmed. Ask how fish was caught: pole-and-line and hook-and-line have little bycatch; bottom trawling and some longlines have much. Use the whole fish: head and bones for stock (XXII.1), trimmings for fishcakes. Local guides — Seafood Watch in the US, the Good Fish Guide in the UK — rate species by region.

At the stove

At the fish counter or in the freezer aisle, note which products carry an MSC or ASC label, where they were caught or farmed, and by what method. Choose one species you have not cooked before.

Peru's anchoveta fishery, the largest single-species fishery on earth, catches several million tonnes a year in good years; most of it becomes fishmeal and fish oil for aquaculture and animal feed elsewhere in the world.

Terms

Overfished
A stock fished faster than it can replace itself.
Aquaculture
Farming of fish, shellfish and seaweed.
Fish in : fish out
Kilograms of wild fish in the feed per kilogram of farmed fish produced.
Bycatch
Animals caught unintentionally while fishing for others.
More than a third of stocks are overfished, and half of seafood is now farmed. A farmed fish's footprint depends on its feed. Choose small fish, bivalves and herbivores, read MSC and ASC labels, and use the whole fish.

Sources

  1. FAO, The State of World Fisheries and Aquaculture 2024: in 2021, 62.3 % of assessed marine stocks were fished within biologically sustainable levels, against 90 % in 1974; in 2022 aquaculture produced 94.4 million tonnes of aquatic animals, 51 % of the total, overtaking capture fisheries for the first time.
  2. Fish in : fish out — the kilograms of wild fish used to make the fishmeal and fish oil in the feed for one kilogram of farmed fish (IFFO method, with about 22.5 % fishmeal and 5 % fish-oil yield from whole fish); published values for farmed salmon fell from above 4 in the 1990s to around 1 in the 2010s as plant ingredients replaced marine ones.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.