Abstract
The spawning of paired "honmoroko" (Gnathopogon caerulescens), a small cyprinid fish that is endemic to Lake Biwa, was investigated in relation to frequency of spawning, egg hatching rates, and occurrence of deformities in hatchlings through a spawning season. Four female/male pairs, which were reared in captivity in tanks supplied with lake water, spawned 6-9 times/pair between April and the end of June or July, with 44.4-100% (mean 84.6%) of the eggs in each brood hatching. The mean deformity rate of the hatchlings was low (1.5%). These results suggest that "honmoroko" is capable of normal spawning in pairs even though this species usually exhibits polyandrous spawning in nature, and that pair spawning can reveal some detailed reproductive traits of this fish.
