The present paper deals with the studies on the spawning season of fishes in Ogasawara Islands. The results obtained were as follows.
1) Basing on the monthly change of Gonad Index (GI), spawning season of
Herlotsichthys quadrimaculatus is estimated to be from mid March to the end of August. An adult female (14.7cm FL) carried 64720 eggs and egg-diameters varied from 1.30mm to 1.63mm, then average 1.41±0.08mm. The ratio of males to females varied from 0.45 to 2.48.
2) The reversing eggs in
Ablennes hians,
Platybelone argala platyula and
Tylosurus acus melanotus were confirmed in June 13, 1985. The matured eggs of
T. acus melanotus was spherical, 3.49±0.07mm (3.40-3.60mm) in diameters, with about 100 tendrils distributed over the surface.
3) Matured eggs of
Hemiramphus lutkei and
Euleptorhamphus viridis were observed in June 13, 1985. The egg-diameters of the former was 2.06±0.09mm (1.85-2.20mm) with 28-30 tendrils, the latter was 1.85±0.08mm (1.66-1.94mm) with 40-50 tendrils.
4) According to the Gonad Index and situation of matured eggs carried, the following flying fishes seem to be spawn from May to June.
Matured egg diameters was 1.31±0.07mm (1.20-1.40mm) in
Parexocoetus brachy-pterus brachypterus, 1.38±0.03mm (1.34-1.44mm) in
Cypselurus poecilopterus, 1.18±0.04 mm (1.12-1.24mm) in
Cypselurus suttoni and 1.38±0.72mm (1.30-1.45mm) in
Cypselurus unicolor.
These eggs are spherical with long tendrils. The number of eggs carried from an adult female was 16000 in
C. poecillopterus (21.2 cm FL), 122500 in
C. suttoni (33.5 cm FL) and 37000 in
C. unicolor (31.6cm FL) . During the spawning period, the change of sex ratio differed from one fish to another.
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