Studies on the Spawning Behavior of Chromis notata (Temminck et Schlegel)

The pomacentrid fish, Chromis notata (Temminck et Schlegel) is found around shallow rocky reefs in southern Japan, and is one of the important commercial fishes at the northern coast of Kyushu. In the present study, spawning behavior of the fish was studied with the help of SCUBA, during the period from 1975 to 1978, at Tsuyazaki, northern Kyushu. Results obtained are summarized as follows: 1) The spawning of C. notata starts at the middle of June when the water temperature reaches 20℃, and ends at the middle of August. During the breeding season, spawning occurs about five times at intervals of about a half month. Each spawning period lasts for one or two days during a week from the spring tide to the neap tide. 2) Males of C. notata start to prepare the nests in holes or crevices in the rock, one or two days before the spawning. The males show territorial behavior and guard the nest against the conspecific males. Usually, the nests tend to be concentrated over a relatively narrow area of sea bottom. 3) On the day of spawning, females swim around above the nests of males in schools of 2～15 individuals. When females come near to the nest, the male displays a typical `signal jump\u27 and entices a female into his nest. 4) Soon after entering the nest, the female extends her ovipositor and starts to lay eggs on the inner surface of the nest. After the female lays eggs for a while, the male spawns and fertilizes the eggs. 5) Spawning by pairs kept in aquaria lasted for 1～3 hours, and females laid 12,000～32,000 eggs per spawning. A female laid eggs three times during the period from June 11 to July 26, 1976 and the total number of eggs amounted to more than 80,000. 6) After spawning, the female leaves the nest, but the male guards and fans the eggs until they hatch 3～4 days later. Males seem to take care of eggs laid by 3～4 females at one time. 7) In this report, the sequence of behavior from nesting to care of eggs is described, and underwater photographs of each phase are presented. Differences of spawning behavior between C. notata and several other pomacentrid fishes are discussed.スズメダイChromis notata(Temminck et Schlegel)は,南日本の浅い岩礁地帯に生息するスズメダイ科の全長10cm程度の小魚である.北部九州沿岸ではその生息量が多く,水深10m前後の岩礁域で潜水すると必ず見られる魚である.小型魚で骨が堅く高級魚ではないが,福岡市およびその周辺では本種の塩蔵品を\u22あぶつてかも\u22と呼び,初夏の味覚として賞味している.本種については,藤田(1957)による卵発生と前期仔魚の記載があるのみで,その産卵生態については明らかにされていない.筆者らは,北部九州沿岸に生息する各種の磯魚の産卵生態を潜水観察によつて研究しつつあるが,今回はスズメダイの産卵場所,産卵期,産卵と潮汐との関係,産卵行動などについての潜水観察と水槽内の実験結果について報告する