The present paper deals with gonadal formation, sex succession and sexual function in the Japanese hawkfishes, Cirrhitichthys aureus (Temminck et Schlegel), C. aprinus (Cuvier), C. falco Randall, Cirrhitops hubbardi (Schultz) and Cyprinocirrhites polyactis (Bleeker). Detailed studies were made for C. aureus collected from Suruga Bay, central Japan. In this species the gonad of a young fish of 21.8mm SL had begun to initially differentiate into an ovary forming an early ovarian cavity of the parovarian type. The gonadal structures of 63 further specimens of C. aureus, ranging from 23.9 to 114.3mm SL, could be separated into three categories: viz., ovaries (7), ambisexual gonads (54) and secondary testes (2). Reproduction of C. aureus in Suruga Bay took place from June to November. Although ovaries which appeared throughout the year presented only in the immature stage and occurred only in small fish ranging from 25.1 to 46.6mm SL, functional gonads occurred in 32 ambisexual fish ranging from 61.5 to 113.5mm SL and in one secondary male of 101.5mm SL, collected during the reproductive season. The smaller ambisexual fish, ranging from 61.5 to 92.0mm SL, showed active oogenetic processes in the major ovarian zones with many ripened eggs ovulating into the ovarian cavity. These gynogenic gonads undoubtedly functioned as female; however, distinct meiosis proceeded partially in the minor testicular zones with a few spermatozoa occurring in the was deferens. The larger ambisexual specimens, ranging from 71.5 to 113.5mm SL, had slender androgenic gonads, which showed active spermatogenesis in various testicular zones and which might function as males with reduced ovigerous lamellae. The secondary males had testes occupied by seminal lobules, but which retained the ovarian cavity within. According to aquarium rearing experiments, in a pair of C. aureus twice crossed mutually after spawning, functional sex changes occurred in twice, opposite directions, in a single gonad, i.e., from female to male and from male to female. These gonadal aspects in captive C. aureus seemed to show an intermediate phenomenon between consecutive and simultaneous hermaphroditism. This finding also suggested that C. aureus had similar sex succession characteristics to those of the serranid, Serranus fasciatus, studied by Hasting and Petersen (1986) and the gobiid, Trimma okinawae, studied by Sunobe (1990). We also established that normal functional hermaphroditism occurred in the four other cirrhitid species, which showed almost identical gonadal characteristics to C. aureus.
Morphological changes in free neuromasts are reported from larvae of the Ayu, Plecoglossus altivelis. In newly-hatched larvae, free neuromasts were already recognizable in both the head and trunk. During larval growth, the number of free neuromasts increased, and the number of its sensory cells 2 days after hatching was constant. In the trunk, two types of free neuromasts, one with maximum sensitivity in the antero-posterior direction and the other with maximum sensitivity in the dorso-ventral direction, were observed. The former type predominated. In the head, free neuromasts were located around the eye and nose, their directions of maximum sensitivity forming lines tangential to concentric circles about the eye and nose. Distinct changes in free neuromasts occurred during the formation of the canal organ. The canal organ was first observed in the head region 64 days after hatching and in the trunk region 100 days after hatching. Concomitant with the formation of the canal organ, the profile of the cupulae of the free neuromasts changed from a flat bar to semispherical. Sensory cells in the canal neuromasts did not differ morphologically from those in the free neuromasts. It is considered that there is a close relationship between the sensitivity of the neuromast and the shape of the cupula, i.e., that the free neuromasts are adapted to slow water flow, as in lakes and the sea, while the neuromasts in the canal organ are adapted to rapid water flow.