キジハタの産卵習性と初期生活史
1966 年 13 巻 4-6 号 p. 156-161
詳細
1966 年 13 巻 4-6 号 p. 156-161
Epinephelus akaara (TEMMINCK et SCHLEGEL) is one of the commonly found serranid fishes, and widely distributed in the coastal waters of south-western Japan. From middle of July to early September, 1965, the authors observed the spawning behavior and egg development of this fish at the Hakatashima Station, Ehime Prefecture, and reard its hatched larvae about 2 weeks.
The spawning in the culturing pond (2.4×5×0.7 m) occurred at 3.30 to 4.30 p.m, in every occasion. The successive spawning behaviors are shown in a diagramatic way in Fig. 1. At first the male approached the female gently (a), then both the male and female swam circularly with their operculars ad jointed (b). At the spawn ing, they dashed to and jumped 2 or 3 times above the water surface (c). After the spawning, the male left the female (d). It took about 1-2 minutes for a pair of fish to complete such a spawning behavior.
The egg is pelagic, spherical in shape, measuring 0.70-0.77 mm in diameter. The yolk is colorless, transparent, and without conspicuous structure, containing a single colorless oil globule measuring 0.15-0.16 mm in diameter.
The egg development (Fig. 2, a-f) was much the same as observed on the other agpelic eggs. No pigment cells developed in the egg, but many colorless granules appeared during the embryonic development. The hatching took place in 23-25 hours after the spawning at the water temperature 25.1-27.0°C.
The newly hatched larva is 1.454.56 mm in total length, and the oil globule situated in the posterior part of the yolk. The surface of the body as well as the marginal fin and the yolk is covered with granules. The number of myotomes is 11+14=25 (Fig. 2, g).
The larva attained 2.00-2.08 mm in total length 16 hours after hatching, when. the first appearance of the melanophores was observed on the dorsal part of the alimentary canal.
In 4.5 days after hatching the yolk and oil globule were entirely consumed. The melanophores of the alimentary canal increased in size, and several others were alsa seen in the middle part of the ventral side of the tail (Fig. 2, i).
In 7 days the larva reached 3.83 mm in total length, and the abdominal cavity was thickly coved with melanophores. The anterior part of the dorsal fin base appeared just behind the head (Fig. 2, j).
In 15 days the larva measured 4.05 mm in total length, having long dorsal and ventral spines. The caudal fin was just form.
