The parrotfish, Scarus sordidus Forsskal is widely distributed in the Indo-Pacific region and is the most abundant representative of the family Scaridae in the coral reefs of the Ryukyu Islands, Japan. We studied sexuality and sex reversal, general behavior and spawning behavior of these fish at the island of Kuroshima, the Yaeyama Group, the Ryukyu Islands during the period from October, 1975, to February, 1978. Results obtained are summarized as follows. 1) These fish are strongly dichromatic, with dark brown color phase (initial phase) and pale blue color phase (terminal phase). Initial phase fish consisted of females and males. Whereas, terminal phase fish were restricted to males. S. sordidus is a protogynous diandric species. All females are of initial phase, mature at about 130 mm SL or more. The color of females changes to terminal phase following sex reversal. Primary males mature at about 100 mm SL and change from initial phase to terminal phase at about 150 mm SL. Color change can be artificially induced by injecting testosterone. 2) These fish are omnivorous, and feed strictly on coral polyps and algae. In feeding, they form mixed foraging groups with other scarids, mullids and labrids. Such groups are often attacked by several pomacentrid fishes, which hold territories on coral substrata within the lagoon moat. Individuals within mixed foraging groups, however, can get food from the pomacentrids' territories by swamping. At night, these fish sleep within mucous envelops. 3) S. sordidus spawns from April to August at Kuroshima. Spawning begins immediately after high tide and continues for about one hour at reef channels or outer reef slopes. Both pair and group spawning were observed. Terminal males spawn in pairs with single females, whereas, initial males spawn in groups.
ハゲブダイScarus sordidus Forsskalはインド-太平洋の浅海岩礁に広く分布し,ブダイ科魚類のうちでは全長30cmほどの比較的小型のもので,わが国では大隅諸島から琉球列島に生息している(Gushima and Murakami,1976;吉野ら,1975).Choatand Robertson(1975)はオーストラリアのヘロン島において,本種を含むブダイ類の性転換と産卵行動について研究し,本種が顕著な性的二型を示し,雌性先熟性の性転換を行うことを明らかにした.また,日本産ブダイ類については,ブダイCalotomus japonicus (Cuvier et Valenciennes)の成熟,年齢と成長および資源量(静岡県水試,1974;河尻,1975,1976),ブダイ類の食性(橋本,1977)およびブダイ類を含む磯魚の混成群の生態(具島・村上,1979)などの研究がある.著者らは増殖学的立場から岩礁性魚類の繁殖生態を明らかにする研究を行いつつあるが,その一環としてベラ亜目魚類の産卵行動を潜水観察するとともに,性転換について研究を行つている,今回は沖縄県八重山郡竹富町黒島で調査したハゲブダイの雌雄性と性転換,一般生態および産卵生態について報告する.