<font color='#0000FF'>Been there but havn't dived yet - will try to this year. It has quite a few wrecks, conditions are not the med - more like the Atlantic, so expect it to be cooler and viz more limited. Saying this I consider 20ºc and 10m viz good.
The BSAC web-site has more information on Gib. Gibraltar itself is quite fascinating, a piece of England in Spain (More English than Malaga
). There is quite a bit to see including large caves (land based -not diving). Accomodation is not that cheap though. The border can be a real pain to cross from Gib-Spain, it took me three hours. It's a fascinating place, as for the diving I reckon it should be quite good, curious to go. BSAC trip report
As for the fish there are Dolphins in the bay.