According to the UN's Food and Agriculture Organization, nearly 99 million tonnes of aquatic animals (fish, molluscs like oysters and mussels and crustaceans like prawns) were farmed around the world in 2023, five times more than three decades ago.

Since 2022, the farming of aquatic animals has been steadily overtaking fishing around the world -- but with large disparities from species to species.

- Fast-growing species -

The two biggest sellers on the market in 2023, carp and tilapia, mainly came from freshwater farming, while other widely-consumed fish, like herring, came just from deep sea fishing

Thierry Laugier, a researcher at Ifremer, France's national institute for ocean science and technology, told AFP that fish farmers choose species that grow quickly and with simple requirements, to be able to control the life cycle.

Sales of the most widely farmed fish in Europe, Atlantic salmon, came to 1.9 million tonnes in 2023, 99 percent of which were farmed.

"We know how to control the ageing or how to launch a reproduction cycle, through injecting hormones," Laugier said.

- Asia main producer -

Asia is by far the biggest producer of farmed fish, accounting for 92 percent of the 136 million tonnes -- of both animal and plant species -- produced under manmade conditions in 2023.

"For carp, it comes down to tradition, it has been farmed for thousands of years on the Asian continent," the Ifremer researcher said.

At the other end of the spectrum, sardines and herring are just fished in the oceans, mainly for profitability reasons as some fish grow very slowly.

"It takes around two years to get an adult-sized sardine," Laugier said.

He said farming of some fish has not yet been started as, "for a long time, we thought the ocean was an inexhaustible resource".

- Seaweed -

Little known in the West, seaweed nevertheless accounts for almost a third of world aquaculture production.

Almost exclusively from Asia, seaweed production increased by nearly 200 percent in two decades, to 38 million tonnes. It is mainly used in industry, in jellies, pharmaceuticals and cosmetics, the expert said.

He said seaweed also has the major advantage of absorbing not just CO2 in the oceans, but also nitrogen and certain pollutants.

"And from an ecological point of view it is better to farm macroalgae than salmon," Laugier said.