TESTIS AND ANDROPODIAL DEVELOPMENT IN A VIVIPAROUS HALFBEAK, DERMOGENYS SP (TELEOSTEI, HEMIRAMPHIDAE)

Andropodial and testicular development in a viviparous halfbeak, Dermo genys sp., is described from birth to sexual maturity. Gradual transfo rmation of the anterior seven rays in the male anal fin takes place th rough the 9.0 mm-18.0 mm SL stages. Changes include an increase in num ber of segments in all rays, a thickening of rays 1-5, and marked curv ature of raps 1-7. The 20.5 mm-26.0 mm stages are characterized by dev elopment of the tridens flexibilis, a pair of spines, and a hook, the spiculus, on the distal portion of the second anal-fin ray. Serrations also develop on the second and fourth fin rays. A mature andropodium possesses a pair of well-developed spines and a single, segmented, sic kle-shaped spiculus on the second ray, Testicular maturation coincides with andropodial maturation. Throughout fin transformation, testes co ntinue to develop. Male and female gonads are differentiated at birth. Within the testes, isolated spermatogonia proliferate through the 15. 0-mm stage. By 18.0 mm, late-stage spermatogonia within spermatocysts are evident. By 20.5 mm, spermatocysts containing late spermatids are present. Sexual maturation, defined as presence of mature spermatozoa within testicular ducts, occurs at a length of 22.5 mm or greater. The testes of Dermogenys, which are typical atherinomorph testes, contain large, complete spermatozeugmata within the testicular ducts. These f indings provide a morphological basis for identifying ontogenetic stag es of the anal fin and for recognizing and comparing mature andropodia among species of Dermogenys for use in future phylogenetic analyses.