Small sized (up to 10 cm SL), slender and compressed fishes. Anus just before origin of anal fin; lateral line absent. Eyes large; mouth terminal, protrusible. Single dorsal fin, located at posterior part of body, with 7-20 soft rays; anal fins with 15-19 soft rays; length of anal-fin base longer than dorsal-fin base; pectoral fins rounded, with 14-21 soft rays; pelvic fins abdominal, with 6 soft rays; caudal fin rounded. Scales cycloid, small to moderately large. Color: highly variable, appearing characteristic pattern in each species.|
Similar families occurring in the area. Adrianichthyidae: pectoral fin falcate (rather than rounded); mouth non-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: anal-fin base rather short.
Remarks. Surface-swimming schooling fish, found in fresh- or brackish-waters. Feeds mainly on small insects and mosquito larvae. Oviparous.