Among the cichlids are found some of the most interesting and highly desirable of the freshwater aquarium fish. With well over 1,500 species, and many as yet undescribed, this family is one of the largest. Members range in size from 1 to 36 inches and exhibit an incredible range of body forms, behaviors, and dietary preferences. One nearly universal trait among the family is an amazing degree of parental care of the young. Included among various species are those that take the young into the mouth during times of danger and others that feed the young with specially produced mucus. In nearly all cases, both the parents tend to the young — cleaning both them and the nest site and driving off potential predators.

Cichlids have a pair of pharyngeal jaws in the throat for processing food.

This feature has freed the primary jaws to develop an amazing array of adaptations to deal with specific and unusual food items. Included among this family are fish that feed upon bacteria, other fish, hard-shelled mollusks, and those that graze upon algae. It is speculated that such adaptations have allowed cichlids to become the dominant fish family in many of the ecosystems in which they occur.

One of the most universally recognizable and beloved of aquarium fish, the angelfish hails from the Amazon and Negro river systems of South America. A second species, the deep angelfish (P. altrum) is limited in range to the Orinoco River system of Venezuela and is rarely found in the pet trade. This fish has a combination of interesting behavior and incredible beauty. Long, trailing fins accentuate the height and graceful appearance of the laterally compressed body. The body form and dark lateral bands of the wild, or naturally occurring, color phase of this fish are adapted for life in the reed beds that form its natural habitat. Through selective breeding, a large number of color varieties are now available. A number of unrelated marine fish are also commonly referred to as “angelfish.” While similar in body form to the freshwater angelfish, they are quite different animals and are discussed in Chapter 7.

Angelfish prefer slightly acidic water (pH 6.8) and are carnivorous in nature. Although very adaptable, they are most at ease in heavily planted tanks, where their grace in swimming about the foliage can best be seen. They will accept a wide variety of live, frozen, and flake food, the size of which should be geared for their relatively small mouths.

Angelfish will spawn readily if given the proper environment. Adults should be preconditioned with live food of various types, and, of course, they should be in a secure environment without competing fish. They prefer to lay eggs upon plant leaves but will also use flat pieces of slate. Even among adults, the sexes are very difficult to distinguish. Well-experienced aquarists are able to discern that the line of the body between the “feeler” and anal fin is longer and straighter in the female. The most reliable method of determining sex, however, is to maintain a small group and allow them to pair off naturally. Once the pairs are established, the excess fish can be removed to other aquariums. The adults will clean off the spawning site and guard the eggs.

Upon hatching, the young have an adhesive-producing gland on their heads, which allows them to stick to the plant's surface. The adults may be seen frequently taking the fry into their mouths and spitting them back out, apparently cleaning them. Any that miss the plant and float to the bottom are quickly rescued and returned to the nursery area.

Appearing to be clothed in velvet as opposed to scales, this large (12 inches) South American cichlid is quite popular in the pet trade, despite certain drawbacks. It can be acutely pugnacious and will likely consume or attack any and all tank mates. It is, however, a fairly hardy and incredibly interesting animal. Nearly all individuals become quite tame, anticipating food upon sighting their owner and readily feeding from the hand.

The dark and rust-colored markings of the wild oscar are quite spectacular, and a variety of captive-bred color variants have also been established, including the very popular red oscar. Oscars are very attentive parents but will tolerate no other fish within the aquarium during the breeding season (and only rarely at other times). If you have the space to accommodate them — for example, a 55- to 100-gallon aquarium — maintaining and breeding a pair of oscars as they raise their numerous fry (up to 3,000) is an undertaking you are not likely to forget. As they are always in great demand in the pet trade, any young produced will likely be snapped up by other hobbyists or pet stores.

Oscars are, unfortunately, among the many species of fish that have been introduced into foreign environments, much to the detriment of the local ecology. In the southern part of the United States, especially in the Everglades National Park in Florida, huge populations of oscars released from the pet trade are decimating populations of local species. Many of these animals have been released by owners who were not prepared to care for their oscars as they grew into adulthood. Be sure to carefully consider the full size of the fish that you purchase, and never release your pet into a foreign environment.

In Lake Victoria and other rift lakes in Africa lives a variety of cichlids that have, apparently, all evolved from a very small number of “parent species.” About 90 percent of these species are endemic to the lakes in which they are found, and this process seems to have occurred in the relatively short time (in terms of evolution) of perhaps 1 million years or so. Up to 200 closely related species, often termed flocks, can be found in one lake. They have developed an amazing array of body forms and adaptations for feeding upon all of the food resources of the particular lake in which they occur. Unfortunately, Nile perch (Lates niloticus) were introduced into Lake Victoria and others in the 1960s to provide a food resource and economic boost for communities in the surrounding area. This large, predatory fish has eliminated nearly all other species in the lake and is now itself disappearing as it runs out of food.

Rift lake cichlids prefer, in general, hard water. Many are denizens of rocky habitats and do best when given a variety of secure retreats. Almost all are extremely active, and the colors of some rival those of marine fish. Many species require a good deal of vegetable material in the diet, but there are exceptions, so be sure to research the fish that interest you before deciding upon a species.