The live-bearing toothed carps are also called topminnows because of the tendency of many species of these basically small fishes to swim and feed near the water surface. The toothed-carps are all from North and South America (none is native to Hawai`i) and many species are very popular in the freshwater aquarium trade. No doubt, some species found in Hawaiian streams have come from cast off aquarium specimens. However, others were introduced purposely to control mosquitos, a practice now thought to have dubious utility (see Gambusia). Poeciliids have become the most abundant fishes in most bodies of fresh and brackish water in Hawai`i. The family is characterized by males having the anal fin modified into an elongated intromittent organ called a gonopodium, used to transfer sperm to females. Males are thus easy to distinguish from females and the various species found here can usually be identified by collecting or observing mature males. Females, on the other hand, tend to be much less showy, and the species not easily distinguished from one another. Poeciliids are omnivores (feed on a variety of plant and animal matter) and give birth to live young.

Dorsal fin positioned more forward, its origin over or in front of pelvic fins

Lateral line scales 27-32. Males closer in size to females and lacking rainbow hues. Color plain to irridescent or with red to yellow coloration on dorsal or other fins

Lateral line scales 27-28. Males with a colorful (yellow, orange to dark red) dorsal fin, usually short and marked in black spots and vertical bars. Females with light orange pelvic fins or a yellow-orange spot at vent.

Males with yellow dorsal and caudal fins, dorsal somewhat flag-like and marked in black spots or vertical bars. Pectoral fin with 13 to 14 rays. Body not as elongated, thickened at the peduncle; color blue-gray, usually with one or more rows of black spots along side; scales edged in black, producing a net-like pattern. Females fins lacking spots,but with yellow patch around vent. Fresh or brackish water; uncommon. Cuba limia

Males lack a sword-like caudal appendage. Neither sex with narrow, lateral red stripe; if fish some color of orange or red, then body stout and mottled

Pectoral fin with 10 to 11 rays. Body short and stout, with males and females similar in size and shape; color mottled black or with splashes of red or orange. Moon or platy

Family CYPRINIDAE

This family is the largest fish family in the world and includes true minnows, carps, and a number of popular aquarium fishes such as barbs, danios, and rasboras. No members of this family are native to Hawai`i. Some species, such as koi and goldfish, have been kept in artificial ponds for decades and have only poorly naturalized—escapees are sometimes encountered. Other species popular for home aquaria do pose a threat to stream ecology when released into local streams. All of the species included in this family are uncommon (Cyprinus carpio) or rare (all others) in Hawaiian fresh waters.

Dorsal fin with fewer than 12 rays; dorsal and anal fins without spines

Mouth with 2 barbels on each side of upper jaw. Many colorful forms in orange, red, black, and/or white; wild forms olive above and yellowish on sides and belly. Introduced to ponds and naturalized in some reservoirs and irrigation ditches. Koi or carp

Light coppery brown and olive green fish with large, irridescent scales, and 5-6 broken bars (black) on upper half of body. To 6 cm (2.5 in). Green barb

Ctenopharyngodon idella (Valenciennes)