Detailed karyotype studies are undertaken in the Indian ricefish, Oryzias melastigma, according to C-banding and silver staining procedures. Erythrocyte DNA content is also measured by cytophotometry. The chromosome number is 48 in diploid consisting of 24 pairs of acrocentrics (NF=48). One pair has secondary constrictions (NORs) near the centromeric regions. Characteristic C-bands are also detected in two pairs. Estimated DNA-value in O. melastigma is 1.8pg per nucleus.
The chromosome-numbers of females in two dragonet fish species, Callionymus beniteguri and C. ornatipinnis, are thirty-eight (2n=38), all being subtelocentric in morphology. In the males of these two species, however, the chromosome number is thirty-seven (2n=37), among which one chromosome is of large metacentric in morphology. Two haploid chromosome numbers, n=18 and 19, are found to occur in the secondary spermatocytes. In the latter with n=18, one large metacentric chromosome is always present in any cell. The metacentric element observed in somatic and germ cells is suggested to be the Y chromosome. Thus, the sex-chromosome mechanism in these two species is inferred to be a multiple system, being an X1X2-X1X2 mechanism in the female, and an X1X2-Y in the male.