Histological Observations on the Ovaries of Two Species of Taeniosomatous Fishes (Lampridiformes) Caught in Waters Adjacent to the Japanese Main Island

Abstract

The ovaries of a large dealfish, Trachipterus ishikawae, 2.47 m in total length, caught off Kumano-Nada Sea, Pacific coast, and two medium-sized oarfishes, Regalecus russelli, 2.92 m and 2.65 m in total length, caught off Wakasa Bay, Sea of Japan, were examined histologically. The dealfish had mature ovaries, 2420 gin weight, those of the oarfishes being immature (180.2 g and 185.8 g). Microscopic examination revealed an ovarian cavity in the central axis of the tubular ovary in both the dealfish and oarfishes. In the former, in addition to ripe eggs, ovulation scars, atretic follicles, oocytes in the yolk vesicle, peripheral nucleoli and chromatin nucleolus stages were seen, whereas in the oarfishes, no ovulation scars were detected. The oocytes, in various developmental stages in both species, were attached to loose connective tissue, i. e., ovigerous lamellae, derived from a thick ovarian capsule of fibrous connective tissue, which was coated with thin mesothelium. Such ovarian architecture was classified as entovarian type, the developmental mode of the ovarian eggs being unequal.