Small to moderate sized (up to 18 cm, commonly to 3 cm), slender and compressed fishes. Anus just before origin of anal fin; lateral line absent. Eyes large; mouth subterminal and superior, not protrusible; lower jaw usually protruding beyond upper jaw. Single dorsal fin, located at posterior part of body, with 5?17 soft rays; anal fins with 16?32 soft rays; length of anal-fin base longer than dorsalfin base; pectoral fins high on side of body, falcate, with 6?16 soft rays; pelvic fins abdominal, with 5?7 soft rays; caudal fin truncate or nearly so. Scales cycloid, small to moderately large, deciduous. Color: body subtransparent with a mid-predorsal dusky line in many species; fins hyaline, often with black and/or yellow markings.|
Similar families occurring in the area. Aplocheilidae: pectoral fin rounded (rather than falcate); mouth protrusible. Phallostethidae: small first dorsal fin present in many species; median fleshy keel on ventral part of body before origin of anal fin; pelvic fins absent; caudal fin emarginate. Poeciliidae: mouth protrusible; anal-fin base rather short.
Remarks. Surface-swimming schooling fish, chiefly found in freshor brackish-waters, but also in coastal areas around estuaries. Feeds on copepods, small insects, and mollusk and crustacean larvae. Oviparous; female carries the fertilized eggs around urogenital opening until depositing those on plants in many species.