The harvest from both aquaculture and capture fisheries relies largely on finfish. By far the most numerous fish species, and those most important to aquaculture and fisheries, are teleosts, or bony fish, which in the sea extend from small "grazing" species such as anchovy to large active predatory fish such as tuna.

A similarly wide range is also found in fresh water, with the most important species from a production point of view belonging to the carp family. These account for over half the total of inland waters fisheries production.

Elasmobranchs or cartilaginous fish, such as sharks and rays, contribute much less to overall fisheries production. As well, although some primitive "jawless" fish such as lampreys and hagfish are also exploited, their significance is merely anecdotal. Likewise, other vertebrates do not feature prominently in the global aquatic harvest, particularly since the exploitation of whales and many other marine mammals has been curtailed.

Among the invertebrates, the Mollusca, which includes squid and octopus as well as shellfish (mussels, oysters, clams) and the Arthropoda, which includes crustacea such as crab, lobster and shrimp, add substantially to fisheries. A number of aquatic plants, mainly algae such as Laminaria, are of great interest, both as food and as a source of additives widely used in the food and pharmaceutical industries.

Detailed information on bio-ecological characteristics, fishing techniques, processing and trade of the main fishery species is collected by FAO and compiled by the Species Information and Data Programme (SIDP) of the FAO Fisheries Department in various forms and media. A list of the most important species for fisheries (around 600) has been established, based on annual landings (over 10 000 tonnes), regional interest from an economic or social point of view or because these species are endangered or threatened by fisheries.

A series of fact sheets has been produced for these selected species, in collaboration with the FAO Fisheries Global Information System (FIGIS) using SIDP database material. The fact sheets provide brief, updated and comprehensive written and graphic species information including nomenclature, description, biology and ecology, geographical distribution and interest for fisheries.