This section contains the common names of the fish identified. The most used common names are included in this section, although some species may have common names not mentioned in this book.

This section includes the most recent (at publication) scientific or Latin name for each species. The first term of the scientific name represents the fish's genus, while the second identifies the species. In some cases, a third term may be used, which identifies the sub-species.

This section includes synonyms (former scientific names currently deemed incorrect), that are most commonly used. For some species, other synonyms may exist, although these are used less frequently than the listed synonyms.

This section includes a written description of the species.

This section describes the maximum length (standard length) that the species may reach. In several cases, a species will attain a larger size in the wild than in aquaria.

Included under "Similar Species" are species that physically resemble the species identified.

The habitat is the geographic origin of the species.

The water level at which the species spends most of its time. Substrate-dependent describe species which adhere to substrates throughout the tank including plants, rocks, wood, and the tank glass.

This section describes the tank requirements of the species. The length measurement applies to the side length of the tank, while the volume applies to the water capacity of the tank. Of these two measurements , the most important is the side length, as the more surface area, the better for fish habitation. For example a 20" (51 cm) or 10 gallon tank, is much more suitable than a 10 gallon with a 16" (40 cm) side measurement. The measurements given should be considered the smallest quarters suitable for the species. In most cases, unless otherwise stated, the tank measurement is suitable for adult-sized fish. Suggestions regarding tank set-up are included in this section.

The values in this section are the range that are tolerable by the species. In parentheses, the ideal water values are stated. Some species prefer the addition of salt to the water. Details to salt content are also included in this section.

This section describes the temperament of the species. Most species can be combined with other species in a community tank. Community tanks are not just reserved for small, peaceful species. A community tank can include peaceful fish, large fish, or aggressive fish if properly selected. In some cases, the method of pairing and method of brood care are included in this section.

Suggested companions are species that are suitable tank mates for the species identified. These are merely suggestions, and other, unlisted companions may also be suitable. However, some of the suggested companions should not be combined with other suggested companions. For example, under Corydoras, suggested companions list both Angelfish and tetras. However, Angelfish should not be combined with small tetras such as neons.

This section suggests the types of foods accepted by the fish. Live foods, when listed, include frozen foods. This section may include feeding tips.

In this category, the characteristics used to distinguish between the sexes are discussed. In some cases, external sexual differences are not apparent.

This section includes notes about breeding, including instructions about initiating the fish to spawn and raising the fry.

The number given is the author's rating for the degree of difficulty in breeding the fish.
1-3 = Breeding is easily accomplished. No special requirements are needed for a successful spawning. Spawning occurs under within the given water perimeters. In most cases, the eggs/fry need only be protected from the parents to have a successful brood. Breeding is easiest in a tank containing only the species, and not other fish, although spawning may be successful in community tanks.
4-5 = Breeding is easy, but takes more effort than 1-3 rated species. 4-5 rated species may require certain water properties to be met before they spawn. Some 4-5 rated fish may express strongly aggressive brood care, and may threaten other tank inhabitants (including mates). Thus many of these species are best bred in a breeding tank of their own. Other 4-5 level species may be easily bred, although the fry are not easily raised.
6-7 = Breeding is moderately difficult due to one or more factors. Generally a breeding tank with specific water conditions is required for breeding. Some species may require conditioning (separating a pair and feeding them frequently with a variety of live foods), and a change in temperature to help initiate spawning. Fish might be difficult to pair and/or bullying may occur between the pair. Some species may aggressively defend their spawn and attack other tank mates. The eggs may be susceptible to infection and/or difficult to hatch. The fry may be difficult to raise. Some larger species may not be particularly difficult to spawn, but may requires a large tank.
8-9 = Breeding is difficult, due to one or several factors. The fish species may be large, and require a roomy species tank in which to spawn. Spawning may be difficult to initiate, and/or pairing may be difficult. In some cases, the species may bully their mate to death. The fry may have special requirements and/or may be difficult to feed and raise.
10 = Breeding is not possible in aquaria or has yet to be accomplished. Details may be know about the species reproductive behavior in the wild, but no reports of captive spawning are available.

This section includes remarks about the species that are not covered in the earlier sections.

This section includes a numeric rating for the degree of difficulty of care of the species. Reasons for the rating follow the rating.
1-2 = Species suitable for a beginner's first tank. These species are hardy and generally tolerant of a wide range of water conditions. Flake foods are readily accepted, and most 1-2 level fish are suited to community tanks. 3 = Species suited for the slightly more experienced aquariast. These species generally accept a range of water properties, although periodic monitoring of water values is recommended. Most level 3 fish are community species and accept flake and other dry foods.
4-5 = Species suited for those aquariasts who can successfully keep lower level species. Level 4-5 species may require live and/or frozen foods in their diet. Level 4-5 species may be less suited to community tanks due to pugnacious or predatory behavior. Level 4-5 species may require a large tank due to their size or social behavior. These species may be somewhat sensitive to water chemistry, and thus the water values should be tested regularly. Some species may require special water conditions such as black water or brackish water. Level 4-5 species may be more susceptible to disease than lower rated fish.
6-7 = Species suited for the experienced aquariast. The species may require a diet including live and/or frozen foods. Some level 6-7 species are territorial and belligerent, and must be carefully monitored in a community set-up with other aggressive species. Level 6-7 fish may grow to a large size, and thus require a spacious tank. Level 6-7 fish may be particularly sensitive to water chemistry, and in some cases, the water should be checked on a weekly basis. Some species are demanding tank conditions, and require a specific tank set-up to thrive. Often level 6-7 species are easily stressed by unfavorable conditions and are especially sensitive to disease and infection.
8-9 = Species only recommended for expert aquariasts having much experience. Level 8-9 species require all the care of lower level fish and more. Water properties must be monitored as numerous species are susceptible to infection when conditions are not perfect. Several level 8-9 species will stop feeding when certain requirements are not met. Level 8-9 species may be picky feeders that may not be inclined to compete for food with more efficient feeders. Many 8-9 rated fish make tank set-up demands on the aquariast. Several level 8-9 species reach and enormous size and thus require a large tank with only large companions. Some level 8-9 species are highly aggressive and predatory and are not suited to "typical" community tanks.
10 = There is only one 10 rated species in this volume, Arapaima gigas. This species is not suited to life in an aquarium due to its size. This species is best left in nature where it belongs.