Morphological and Cytological Studies on the Ironfish Occurring in Niigata and Sado Island

Abstract

During the course of our researches on the racial differentiation of the cyprinid fish, Funa, genus Carassius, a considerable number of the ironfish were obtained in every location of Niigata Prefecture facing the Japan Sea. In order to elucidate the relationship between the ironfish and Funa, morphometrical study and internal anatomy of intestinal pattern were performed. Twelve specimens out of 44 ironfish were employed for cytological observation to determine the karyotype and polyploidy. The length of caudal fin, one of the most peculiar characteristics of the ironfish, varies considerably from the length nearly equal to that of Funa to one half of body length of the fish. The proportional value (total length/body length) of the ironfish was then calculated at 1.38-1.65 (mean 1.49±0.07), whilst the Funa was 1.22-1.38 (mean 1.29±0.03). Most of the individuals of ironfish examined had triploid chromosome numbers (3n = 153). They were all female and were lived together with the Funa with diploid and triploid chromosome numbers. After Kafuku's classification (1952), the intestinal pattern of triploid ironfish was diagnosed as the A-type that is peculiar to Kinbuna and/or Nagabuna. On the other hand, it was difficult to determine the intestinal type of several diploid ironfish (2n = 100) caught in Sado Island, on account of its complexity corresponding to that of goldfish. Therefore, these diploid individuals consisting of both sexes seemed to be the hybrids between the Funa and goldfish. To make comparison of different localities, the chromosome number of 2 individuals of ironfish collected from Lake Utori-numa, Miyagi Prefecture, was examined, and 2n = 100 was estimated.