The Multiple Spawning in Landlocked Dwarf Ayu Plecoglossus altivelis in Lake Biwa

The histological changes of ovaries of dwarf Ayu in Lake Biwa, so-called “Koayu”, during spawning season from August to October in 1980, were examined. And it was attempted to clarify the frequency of spawning and the generality of multiple spawning. Many mature ovaries with empty follicles showed that the fish probably spawns twice at least. The ovaries with empty follicles were classified into three types on the basis of the histological characteristics, ovary after the first ovulation, ovary after the second ovulation and ovary after the third ovulation. A few fishes’ oocytes began to degenerate after the first ovulation. However, it was presumed that the greater part of females spawned twice and a small number of fishes attained the third maturation.