1Lake Biwa Museum, Kusatsu, Shiga 525-0001, 2School of Environmental Sciences, The University of Shiga Prefecture, Hikone, Shiga 522-8533, 3Shiga Prefecture Fishery Experiment Station, Hikone, Shiga 522-0057, Japan
The small cyprinid honmoroko Gnathopogon caerulescens is an endemic species of Lake Biwa, Japan, and a commercial resource for fisheries and aquaculture. In a laboratory setting, using eggs collected in the field, we investigated the relationship between the date of hatching of five successive cohorts of this fish and certain spawning parameters of each cohort at adulthood. Depending on the cohort, adult females spawned on average 3,000-4,000 eggs apiece in 1.5-3.5 mean spawning events between early April (water temperature 10.5℃) and mid-July (25.9℃). Spawning occurred at intervals of 3 to 9 days in May and June in one cohort, but irregularly in the other cohorts. More than 80% of the eggs released were spawned early in the breeding season (at<20℃ water temperature) in the three earlier-hatched cohorts, but the two later-hatched cohorts spawned less than 70% of the eggs during the same period. These data show that G. caerulescens is a multiple spawner with spawning occurring intermittently several times during the spawning season; they also suggest that the date of hatching affects the spawning pattern at maturity.