Priapium Fishes
By Koichi Shibukawa

Neostethus bicornis

Neostethus lankesteri

Small sized (up to 3.7 cm), delicate fishes. Body slender and compressed; bilaterally asymmetrical priapium with one or two elongate, rod-like external priapial bones (ctenactinia or toxactinium) under throat of male; anus below pectoral fin; median fleshy keel on ventral part of body before origin of anal fin; lateral line absent. Eyes large; mouth subterminal and superior; lower jaw protruding beyond upper jaw. Single or two dorsal fins; first dorsal fin absent or present with one or two spines or thickened rays; second dorsal fin with 5-10 soft rays; anal fins with 14-28 soft rays; pectoral fins with 9-13; pelvic fins apparently absent (modified into portion of priapium in male, vestigial or absent in female); caudal fin emarginate. Scales small to moderately large, cycloid, deciduous. Color: transparent to opaque, with scattered melalnophores on head and body.

Similar families occurring in the area. Adrianichthyidae, Aplocheilidae, and Poeciliidae: no median fleshy keel on ventral part of body before origin of anal fin; pelvic fins present; caudal fin rounded or truncate.

Remarks. Chiefly found in brackish waters, but also in coastal and freshwater areas. Schooling. Feed on copepods and mollusc larvae. Oviparous but fertilized internally, and subsequently female lying fertilized eggs.