Morphological development of the oriental goby, Acanthogobius flavimanus reared from eggs to juveniles in the laboratory at Sagami Bay, Japan is described. During mid February ovarian maturation is successfully induced by injection of the LH-releasing hormone of Gonadotropin. The dose of the hormone was 5IU/g body weight and was injected 4 times at an interval of one day for ovulation at water temperature of 12 to15°C. Artificial fertilization was accomplished on the first of March, 1985. The numberof ripe eggs removed artificially was about 25, 000. The eggs immediately after insemination are spherical in shape, measuring 0.99-1.10 mm in diameter. They have a bundle ofadhesive filaments at their basal end and a cluster of small oil globules. The egg membrane elongates to form a perivitelline space when the inflation ceases about 30 minutes after insemination. The eggs alter ellipsoid shape and measure about 3.93 mm on the long axis. Hatching began about 18 days after insemination at water temperature of 15.0-15.4°C. Soon before hatching, embryos fold down the tail at the basal end region of eggshell. The newly hatched larvae are 4.13-4.86 mm in total length (TL), with 31 (13+18) myomeres. The larvae usually lay on their body on the bottom of the aquarium. Many melanophores and guanophores are distributed on eye cups, gas bladder, intestine and in the caudal region. Complex of pigments form a band in the caudal region, but the band is never connected with the pigments on intestine. This character is not shared with larvae of A. hasta and A. lactipes. Seven days after hatching the yolk was completely absorbed and the larvae attained a total length of 5.73-6.10 mm.The larvae swim actively in the aquarium and start to practice feeding on the rotifer. Twenty days after hatching, the larvae averaged 9.01 mm in TL and the caudal notochord flex at 45°. Rudimental second dorsal, anal, caudal and ventral fins are also formed. The larvae attained 11.00-15.00 mm in TL, thirty five after hatching, are found to transit the bottom-life and first dorsal and ventral fins are completely formed. During the late postlarval stage, the fish is nervously to develop the free neuromast on the skin surface. The larvae reached the juvenile stage at 45-50 days after hatching and attained 13.85-24.90 mm in TL. At this period all scales appeared on the body. A clear black spot on the first dorsal fin is characteristic at the immature stage of the fish. The larvae and juveniles were reared by feeding them with the rotifers, Artemia nauplii, krill meat and lugworm meat for one year. The growth of larvae and juveniles in 1985 is expressed by the following equations.
Y1=4.697×1.034x (0≤X≤45)
Y2=0.716X-14.123 (46≤X≤170)
Y3=160.18lnX-715.90 (171≤X≤330)
where Y is the total length (mm) and X is number of days after hatching. The fish grew to 189.55-232.70 mm in TL and became mature in one year. Most of the individuals attained gonadal maturation and died after spawning.
