A study was carried out to clarify the spawning of a file-fish, Navodon modestus (GÜNTHER), in the Bingo Nada area, as a serial study on the spawning ecology of the commercially important fishes in the central part of the Inland Sea of Japan.
As described in previous paper, the file-fish are caught abundantly by the masu-ami, a kind of pound net, in Bingo Nada, operated during the three months from April until June. Since most of the fish in these months have well developed gonads, they are considered to be spawners.
Observations on ovaries of several samples taken at different times from March through May indicated a rapid development of ovaries during the period. From the analysis of the frequency distribution of diameter of ovarian eggs, the spawning of Navodon modestus may occur at least more than once during the spawning season.
On the basis of the catch records and from the nature of the eggs of the aluterid fishes in general, it was presumed that the file-fish may spawn somewhere along the coasts of islands in Bingo Nada. Efforts had been devoted to find the eggs spawned in nature, especially in Sargassum zones along several islands. A large amount of Sargassum, together with the bottom sediments nearby, were collected at low water and thoroughly examined. Finally, in early June, 1963, 92 eggs were found among Sargassum serratifolium collected near St. I, located at south-western coast of Hashiri-shima.
These eggs were identical in structure and size with the eggs of Navodon modestus obtained by artificial fertilization. It was thus made clear that some of the file-fish may spawn in Sargassum zones.
A consideration was given on the possibility that the eggs of Navodon modestus may not so firmly adhere to substrates in nature as in the laboratory.