The Early Life History of the Combtooth Blenny Dasson trossulus and Spawnings of the Laboratory-reared Fish about Three Months after Hatching

The combtooth blenny Dasson trossulus (JORDAN et SNYDER) is distributed in coastal waters of the middle and southern Japan. It mainly feeds on attached diatoms and grows to 11mm TL when fully grown. The egg masses of the fish were collected with artifical nests of the oyster shell, the pecten shell, the conch shell, the pen shell and vinyl choride pipe which were hung or set in Nomo Harbor (Lat. 32°35.3'N, Long. 129°45.5'E) near Nagasaki City in the western Kyushu. They were collected from June to August in the years 1968, 1969 and 1971. The embryonic development of the eggs was traced. The larvae hatched out from the collected egg masses were reared in 30ℓ or 50ℓ translucent plastic vessles. The larvae were successively fed with organisms of the rotifer Brachionus plicatilis, nauplii of Artemia salina, copepods of Acartia collected with lamp and the splash copepod Tigriopus japonicus as they grew larger. The observation on the morphology and behavior of the reared larvae and juveniles was carried out. The young, hatched out on June 8, 1969, grew to about 30mm TL in 30 days after hatching and were transferred from the vessle to a half ton concrete tank. They were fed with the meat of Japanese anchovy. They ate the meat well and grew to over 60mm TL in three months after hatching. They spawned egg masses in a vinyl pipe and an earthen pipe in September 13 and 14 of the same year. They spawned 96 days after hatching under the natural conditions of temperature and light. In 1971, the reared larvae, hatched out on July 2, grew to about 70mm TL and first spawned on October 5, 95 days after hatching, when the water temparature was 24°C, and they spawned until November 16 of the same year when the water temperature dropped to 19.8°C. The examination of larvae and juvenile specimens collected from the coastal waters near Nagasaki does not indicate whether the larvae hatched out at the sea in summer grow to adults and spawn within the year or not. But, the cause of the early spawnings above mentioned of the reared fish seems to be that the fish were fed with the anchovy meat in the tank whereas in the sea the fish usually feeds on diatoms