Overfishing is when fishermen use unsustainable ways to catch fish causing them to go into very low numbers
The do's and don'ts is to not buy cheap fish and to look for fish at a store with high turnover.
A case study for atlantic bluefin tuna says that "In 2009, WWF predicted that without drastic measures, Atlantic bluefin tuna will disappear by 2012
A sustainable fishing method is "Hook and Line fishing" where you use a line and several hooks. I told you about hook and line fishing because it stops fish depletion by making it easy to stop bycatch