The issue...

Overfishing means to deplete the stock of fish in (a body of water) by too much fishing. It could potentially bring some fish species to extinction.

Ending Overfishing

More info

-two issues of overfishing is that it can make some fish extinct and that it can mess up the lives of ourselves too, we depend on fish for many things, not just eating. It can also ruin the ecosystem in a cycle sort of way.