If you're worried that your fish supper is adding to problems of over-fishing then check out the Marine Conservation society's website. It's got a full and up-to-date list of fish not to eat.
These are some examples taken from the website in August 2004. The society says that these are best avoided to help conserve fish stocks.
- Atlantic cod
- Atlantic halibut
- Atlantic salmon - wild caught
- Patagonian toothfish
- Tuna (unless it's dolphin-friendly caught with a pole and line or by trolling a jig)