VIVIPARITY IN THE HALFBEAK GENERA DERMOGENYS AND NOMORHAMPHUS (TELEOSTEI, HEMIRAMPHIDAE)

Gravid ovaries were examined histologically from two species of Nomorh amphus and 21 populations of Dermogenys. In addition, changes in dry-w eight throughout gestation are provided for 15 populations. The ovarie s are paired organs running along the lateral body wall and are separa ted along most of their length. In all specimens examined, embryos are fertilized within the ovarian follicle. Viviparity in these species i s divided herein into five categories designated types I-V. In types I and II the entire gestation period is intrafollicular, whereas in typ es III-V only the early stages of gestation are intrafollicular with t he major period of development occurring in the ovarian lumen (intralu minal). Type I is characterized by the retention of a large amount of yolk throughout gestation. Superfetation is not observed. Populations of D. pusilla from Vietnam and Thailand decrease in dry-weight through out gestation. This, coupled with the slight vascularization of the yo lk sac, suggests strict lecithotrophy. Populations of D. pusilla from Singapore and Bangladesh undergo an increase in dry weight and exhibit an increased vascularization of the yolk sac, suggesting a form of un specialized matrotrophy. Type II is characterized by a small amount of yolk, an expansion of the coelomic cavity and pericardial sac, and a simple cuboidal epithelium on the general body surfaces. Superfetation occurs with up to three broods present within a single ovary. Dermoge nys pusilla from Sabah, D. orientalis and Dermogenys sp. (Sulawesi) ex hibit the type II form of viviparity. Dermogenys vivipara from the eas tern Philippine islands of Culion and Busuanga exhibit characteristics considered intermediate between type I and II. These results are comp ared with those from other viviparous species exhibiting intrafollicul ar gestation. In species with types III-V (intraluminal gestation), de veloping oocytes are restricted to a distinct ridge of ovigerous tissu e extending along the entire length of the ovary. Two species, D. vivi parus (Luzon, Philippines) and Dermogenys sp. (Luzon) have the type II I form of viviparity. In this form, oocytes are small (0.8-1.0 mm) wit h little yolk reserves and embryos, covered with a simple cuboidal epi thelium and possessing an expanded belly sec, are retained within the follicles until a late fin-bud stage. Type III embryos found within th e ovarian lumen have a greatly expanded belly sac and remain covered b y a simple cuboidal epithelium until parturition. Superfetation is pre sent in these species with two broods observed simultaneously within a single ovary. Five species, D. megarrhamphus, D. weberi, D. viviparus (Jolo, Philippines), Nomorhamphus sp. (Sulawesi), and N. towoetii, we re observed with the type TV form of viviparity. Embryos in this categ ory are evacuated into the ovarian lumen prior to a fin-bud stage and retain a large yolk mass throughout development. Superfetation is abse nt in these species. A different form of viviparity (type V) is presen t in D. ebrardtii in which embryos appear to obtain nutrients through a form of oophagy and aldelphophagy (feeding on developing oocytes or less-developed siblings). In all specimens with intraluminal developme nt, atretic oocytes within the ovigerous ridge are abundant. These fin dings support the hypothesis that current species and generic limits m ay be artificial and underscores the potential of histological evidenc e for phylogenetic analysis of this group. (C) 1997 Wiley-Liss, Inc.