Knowledge of fish classification is not necessary to use the guide. Fishes are presented in groups of species that share body structure, activity or habitat characteristics. Each illustration within a group includes a brief descriptive account containing important characteristics for identification of that species, notes on similar species, notes on natural history or habitat, geographic distribution, and average size of the species.

The best way to use the guide is to become familiar with the arrangement of the species groups and the major external features and descriptive terms used in fish identification (Figure 4 and Glossary). Simply flipping through the pages of illustrations for each group may be the quickest way to find a collected or observed fish. Once a corresponding illustration has been located, the species account should provide enough information to help identify it. A common name may help to locate it using the index at the end of the guide; however, common names are often unreliable since they vary widely from place to place.

Figure 4. Basic external features of a bony fish.

SCUBA divers will find that knowledge of the fish's shape, coloration, habitat or activity may help to identify it. Written notes and sketches, including behavioral observations are particularly useful.

Each species account contains the American Fisheries Society common name (Robins et al. 1980), local or other common names, scientific name, key characteristics that distinguish that species from related species, natural history notes, geographic distribution and average (not maximum) adult size in inches or feet total length. The index contains both common and scientific names.

The scientific name consists of a genus name which is always capitalized and italicized (or underlined) and a specific or species name that is never capitalized but always italicized (or underlined). The genus level of a natural clasification indicates similarity among closely-related organisms. The species level indicates the differences between closely-related but not interbreeding kinds of living things. For example, young Scomberomorus cavalla, king mackerel closely resemble Scombermorus maculatus, Spanish mackerel, in coloration and shape but the two are distinct species and can be separated easily by looking at the lateral line and gill rakers. Learning to recognize the distinguishing characteristics is the key to knowing the species.