Embryonic Development and Metamorphosis after Hatching in the Sharksucker, <I>Echeneis naucrates</I>
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概要
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The sharksucker, <I>Echeneis naucrates</I> Linnaeus was spawned from June 2nd to August 7th, and from September 18th to December 3rd in a tank of Oita Ecological Aquarium.Embryonic development and metamorphosis after hatching were observed.<BR>Spawning activities were continued for 30 minutes between 18: 20 and 20: 00.Lights for exhibition were put out at 18: 00.The spawning behavior was always repeated 2-5times with-in 30 min in the daily spawning period.The temperature of the breeding aquarium was regulated from 27.5 to 30.5°C.<BR>Fertilized eggs are transparent and free floating.Eggs are rather large, 2.62 mm in diameter, and nearly spherical in shape.One to five yellowish oil globules (2-3 in average) measuring 120 to 170 μ in diameter are found on one side of the vegetal pole.Time intervals of embryonic development after fertilization were summarized in Table 1.<BR>Mouth cleft appeared 2 days after hatching.The mouth and anus were well formed and open, the tail showed a fan-like shape and the yolk mass was completely absorbed on 4th day.On 6th day, the larvae attained 12.0 mm in total length and several pieces of small hooklike projections appeared on the anterior part of each jaw.<BR>When larvae measured up to 15-20.5 mm in total length 9 days after hatching, the epidermal boarding bulge appeared on the median line of the dorsal part of the body above the basal part of the pectoral fin.The caudal fin was twice as long as the head.The number of fin rays reached the fixed number of the species.<BR>Larvae grew to 29 30 mm in total length 12 days after hatching, and the epidermal bulging shifted to the upper part of the posterior margin of the eyes, forming a sucking disk in an oval shape.When larvae reached 34.0 mm in total length (14th day), the anterior margin of sucking disk extended above the middle of the eyes.On 15th to 20th day, the anterior margin of the sucking disk reached above the anterior margin of the eyes.<BR>Young fish grew to 41.0 55.0 mm in total length 20 N 27 days after hatching, and the anterior margin of the sucking disk reached the anterior margin of the upper jaw.In young fish, 80 mm in total length on.50th day, the sucking disk enlarged to a length longer than the head.The length of the tail reduced.<BR>|The first small scales appeared scattering on the lateral side of the young fish when they attained the size of 75.5 mm in total length.
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