[thunfischtoast]

Calculate the maximum sustainable amount of fish that can be caught/harvested, limit the world-wide production to that and let the market handle the rest.

Those limits would have to be enforced useing armed boats however - else I don't know if there would be an effective way for those huge swimming fish factories to just catch everything until the ecosystem collapses.

Then you'd also need a mechanism so make it socially balanced, or we'd pretty much ban low-incoming fishing societies from consuming their own product.

My humble opinion, not an expert.

[zo1]

This is almost up there with "people shouldn't have kids they can't afford to take care of". The world's appetite for such drastic measures is not anywhere close to being there yet. As evidenced with how barely-able we are to get people to kinda pretend and kinda do something but not really about something as simple as dirty-coal burning, or throwing plastic trash into rivers.