You can check out the following fishing related data in the new Achievements > Statistics > Secondary Skills window:
(Also shows cooking and first aid info. My current data shown as an example)
Fishing Skill: 375/450
Fish caught: 2687
Fish and other things caught: 4929
Fishing daily quests completed: 15
Note the, almost half actual 'fish' (as defined by GM recently) to fish 'and other things caught'. Once they update the achievement for 'Catch xx fish' to include all fished items, it will properly reflect the actual number fished up.
Also this should mean that further increases to numbers caught achievements i.e. 5000 fish caught etc will be retrospective to the start of patch 3.0.2, and it is likely to happen in a future patch from recent GM post:
Tigole
Blizzard Poster
3. Re: Fish caught achievement 10/30/2008 01:17:07 PM PDT
Currently, 1000 fish is the extend of the achievement.But we can definitely add more in a patch.