There are many online resources for fish identification, both tropical and saltwater. Some branches of the Department of Natural Resources offer identification charts for local aquatic life online, and there are many aquarium keeping forums and websites that also offer extensive identification libraries.
Websites for local DNR offices in the area of interest often offer images and charts of local aquatic wildlife. Some public aquariums have online identification galleries for the aquatic life housed in their facilities, and there are countless aquarium hobbyist websites that offer galleries, including Aquahobby.com and Fishchannel.com. There are also a few identification guides for scuba divers, which primarily feature saltwater reef fish and crustaceans.