Taxonomy of Finfish (1+2)

6.1.9 Sex Chromosomes in Fishes

At present, several types of heteromorphic sex chromosome have been described in nearly 100 species from about 1,700 karyotyped.

Almost all types of sex chromosomal mechanisms such as male heterogamety, female heterogamety and multiple sex chromosomes are observed in fishes. This is quite expected since they display almost all types of sexuality found among the vertebrates. Male heterogamety, that is XX-XY sex chromosomes, is more prevalent among fishes than the female heterogamety (ZZ-ZW). Male heterogamety, for example, is found in some deepwater fishes and female heterogamety in several species of catfishes. The occurrence of multiple sex chromosomes was reported in few species like Chiondraco harmatus, an Antartic fish. The sex chromosomes in lake trout (Salvelinus namaycush) could be detected by banding techniques. The X and Y chromosomes in this species are distinguishable by the prominent C-band on the X-chromosomes, which is much reduced in case of the Y-chromosomes. The recognition of sex heterochromatins, including molecular approach with sex-specific DNA probes as done in humans and domestic mammals, will bring many new data about sex determination systems in fishes.