Development of Eggs, Larvae and Juveniles of the Gogy Glossogobius olivaceus Reared in the Laboratory

Abstract

The egg, and larval development of the gobioid fish called “Urohaze”in Japanese, Glossogobius olivaceus are carried out on August, 1986. Hatched larvae are reared for a period of 380days. The spawning period extended from the beginning of August to the mid of September. The ripe egg immediately after insemination is pear in shape, measuring 0.75-0.81mm in long axis and 0.29-0.38mm in short axis, which a boundle of the adhesive filaments at its basal end and a cluster of small oil globules. The number of ripe eggs per spawning is ca. 60, 000. The egg membrane elongated to form a perivitelline space when the inflation ceases 30 minutes after insemination. The egg altered ellipsoid in shape which measured about 2.61mm in long axis and about 0.46mm in short axis. The incubation period was about 79 hours at a water temperature of 22.4-26.3°C. Soon before hatching, the tail of larva never attached to the basal end region of the egg-shell. This character is not shared with larvae of many other gobioid fishes during embryonic development. The newly hatched larvae measured from 2.27-2.37mm in total length (TL), averaging 2.34mm in TL and swim freely in an aquarium. At yolk absorption, 6days after hatching, the larvae attained 2.29-3.10mm in TL and started to practice feeding on the small rotifer, 100-150μm in size. Eleven days after hatching, the larvae are averaged 4.16mm in TL, the caudal notochord flex at 45° and rudimental the second dorsal, anal, caudal and ventral fins are formed. Twenty-five days after hatching the larvae reached the juvenile stage at 7.72-8.88mm in TL and were found to carry the bottom-life.On the 45th days, all scales appeared on the body. A clear black band which cuts across from the mid of lower and upper jaws to the mid of facial region is characteristic at the immature fish stage. The fish grew to 126.05-164.50mm in TL and some individuals became mature in one year. Almost fishes seem to become mature in two years and die of spawning.