Sexual differentiation, gonad development, and spawning seasonality of the Hawaiian butterflyfish, <Emphasis Type="Italic">Chaetodon multicinctus </Emphasis>

The reproductive biology of the coral reef butterflyfish, Chaetodon multicinctus, was investigated by histological examination of gonads sampled over an 18 month period from a shallow inshore population on Oahu, Hawaii . Most gonads developed directly from previously undifferentiated tissue . Ovarian development (the structural formation of lamellae and primary oocytes) was observed in fish >_44 mm and testicular development (the formation of spermatogenic crypts) in fish >_62 mm standard length (SL) . In addition, testis formation was identified within the ovarian lamellae of several differentiated but immature fish . It is hypothesized that prematurational sex change may facilitate monogamy within the highly competitive social structure of this site attached species . Oocyte development in mature females was marked by distinct phases of primary growth, the formation of yolk vesicles, and vitellogenesis . Spawning activity was histologically identified by the maturation and hydration of fully yolked oocytes, and presence of postovulatory follicles . Recently spawned females from field collections and experimental gonadotropin-treatments exhibited postovulatory follicles that were estimated to persist at least 24 h after ovulation . Atresia of yolked oocytes was classified into four stages of cell degeneration and resorption . Monthly analyses of oocyte development and atresia within the sample population show that C . multicinctus has a protracted annual spawning season with a major peak during the early spring and evidence of spawning activity among some individuals in the fall . Histological analyses of spawning activity provide more accurate and unambiguous information than do traditional gonadosomatic assays in this and probably other coral reef fishes .