コウライアカシタビラメの成熟促進, 卵発生と飼育による仔稚魚の形態

抄録

Cynoglossus abbreviatus spawns from mid-March to mid-April in the Sea of Shimabara in Kyushu. During the spawning season ovarian maturation was successfully induced by injection of the pituitary homogenate of Hypophthalmichthys molitrix. The dose of the aceton-dried pituitary homogenate was 6.5 mg/kg body weight of C. abbreviatus. It took about 2 days for ovulation after injection at a water temperature of 14 to 16°C. Artificial fertilizations were accomplished on March 29, 1974 and again on April 7, 1984, using the females matured by hormone injection in the latter case only. The larvae were reared on the rotifers, Artemia nauplii, Tigriopus japonicus and copepods collected from the sea over a period of 113 days in 1974 and 58 days in 1984. The eggs were pelagic, spherical, 1.19-1.23 mm in diameter and had 30-50 oilglobules of 0.068-0.095 mm in diameter, and the perivitelline space was narrow. The incubation period was 90-98 hours at a water temperature of 14 to 16°C. The newly hatched larvae were 3.18-3.45 mm TL and had 61-64 myomeres. The larvae had many melanophores and xanthophores on the body, forming three bands on the caudal region, but were lacking chromatophores on the finfolds. The yolk was completely absorbed when the larvae attained a size of 4.7-5.6 mm TL 8 days after hatching. A single elongated dosal fin ray developed on the head in the 8-day old larvae. The ray was reduced in size as long as the other rays 1 or 2 days after metamorphosis. The rudiment of pectoral fins were found on the both sides of the body in the 2-day old larvae, but two of them disappeared after metamorphosis. A pelvic fin first appeared as a ventral bud just anterior to the gut in the larva of 8.39 mm TL. The full count of 4 rays was observed on the larva of 10.83 mm TL. Metamorphosis began 22 days after hatching when the larvae were 11.20 mm TL. The right eye began to shift the left side of the head at night and reached to the final place after 8.5 hours. It took about 36 hours to complete the metamorphosis, including the eye movement and fusion of the hole in the rostral beak. At the last stage of metamorphosis, the dosal, caudal, anal and ventral fins became confluent. The larvae reached the juvenile stage at a size of 13.5-14.0 mm TL, approximately 28 days after hatchling. The growth of larvae reared in 1974 is expressed by the following equations:
Y₁=3.448·1.0507^x (8≤X≤28)
Y₂=6.3322·1.0275^x (28≤X≤75)
where Y is the total length (mm) and X is the number of days after hatching. Growth rate changed after metamorphosis.