Well, there are a couple of ways. It depends on what you know, such as category or country of origin.
On the main introductory page, type in a common name, such as "stingray", and the next page will list the species that correspond to that general common name. It lists the common name, country, species name and type. Look under "type", which gives a description of the name, such as vernacular, FAO, AFS, market, and so on, including aquarium. So, the first species listed on that page descibed as aquarium, from looking up the common name "stingray", is the Blue spotted stingray ( Taeniura lymma). (So very pretty.)
Click on the link for that species, and that leads you to the species page, which has information like occurance, pictures (hopefully), reproduction and other fun scientific things, which you generally reach by links.
All species pages list the importance of that species, which is on the main species page, under name, order, size, etc. In the case of the blue spotted stingray, the importance is listed as "fisheries: commercial; gamefish: yes; aquarium: commercial". The important part to you is the aquarium:commercial. All species pages list importance, be it commercial fishery, aquarium trade or none at all.
The other method is to go to the main introductory page, and scroll down until you reach "Information by Country/Island", then pick a country, and make sure "aquarium trade" is selected, which will give you all the aquarium fish species listed for that country, both fresh and salt water.
Sorry about the painful detail, Fishbase is a good site, especially for scientific things, but it's a bit enraging too. I hope I explained well enough. Also, you might want to use one of the mirror sites, they are in English, despite being located in Germany and France. The American one is often down or very, very slow. Good luck finding the stingray.
