Global fish production is approaching its sustainable limit, with around 90% of the world’s stocks now fully or overfished and a 17% increase in production forecast by 2025, according to the UN Food and Agriculture Organisation (FAO).

Overexploitation of the planet’s fish has more than tripled since the 1970s, with 40% of popular species like tuna now being caught unsustainably, the UN FAO’s biannual State of the world’s fisheries report says.

Manuel Barange, the UN FAO’s fisheries director, told the Guardian that overfishing rates of around 60% in the Mediterranean and Black Sea regions were “particularly worrying”.

He said: “There is an absolute limit to what we can extract from the sea and it is possibly very close to current production levels, which have stabilised over last few years. They have grown a little in recent years but we don’t expect much more growth because of the rampant increase in aquaculture production.”

Aquaculture is now forecast to overtake wild-caught fish as the source of most fish consumption in 2021, for the first time.

The rise of aquaculture has also benefitted trade, employment and diets in the developing world, with global per capita fish consumption estimated at a record 20 kilograms.

“My personal view is that it is quite momentous to have reached this level of production,” Barange said. “In the struggle to make sure we have enough food to feed more than 9 billion people in 2050, any source of nutrients and micronutrients is welcome.”

Some campaign groups though fear that aquaculture may introduce invasive species, diseases and parasites. The potential for chemical pollution and use of transgenic species are also causes for concern, as are the impacts on wild fisheries and natural habitats.

Shrimp farming is thought to have led to the destruction of 3m hectares of coastal wetlands, including many mangrove forests, and the UN FAO is currently drawing up guidelines to reduce such environmental footprints.

Lasse Gustavssin, the director of Oceana, a marine conservation body, said that sustainable fisheries management should be prioritised instead.

“We now have a fifth more of global fish stocks at worrying levels than we did in 2000,” he said. “The global environmental impact of overfishing is incalculable and the knock-on impact for coastal economies is simply too great for this to be swept under the rug any more.”

For the UK, Brexit could have a big impact on fish-eating patterns. “One thing very likely to happen is that the drop in the value of the pound will makes fish imports into the UK more expensive, and exports cheaper,” said Barange, who lived in Britain for several years. “The UK is a net importer of fish so the fish we eat might cost us more. The fish our industries export will benefit as they will be more competitive pricewise.”

Globally though, some of the biggest beneficiaries of the growing fish industry will be found in the developing world, where fish exports in 2014 exceeded the combined net trade revenues from meat, tobacco, rice and sugar.

Of the world’s top 30 fish consuming nations, 22 were in the UN’s “low income, food deficit” category.

Twelve percent of the world’s population now relies directly or indirectly on the fisheries industry.