http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

Although the sex-determining gene Sry has been identified in mammals, no comparable genes have been found in non-mammalian vertebrates. Here, we used recombinant breakpoint analysis to restrict the sex-determining region in medaka fish (Oryzias latipes) to a 530-kilobase (kb) stretch of the Y chromosome. Deletion analysis of the Y chromosome of a congenic XY female further shortened the region to 250 kb. Shotgun sequencing of this region predicted 27 genes. Three of these genes were expressed during sexual differentiation. However, only the DM-related PG17 was Y specific; we thus named it DMY. Two naturally occurring mutations establish DMY's critical role in male development. The first heritable mutant--a single insertion in exon 3 and the subsequent truncation of DMY--resulted in all XY female offspring. Similarly, the second XY mutant female showed reduced DMY expression with a high proportion of XY female offspring. During normal development, DMY is expressed only in somatic cells of XY gonads. These findings strongly suggest that the sex-specific DMY is required for testicular development and is a prime candidate for the medaka sex-determining gene.

DMY is a Y-specific DM-domain gene required for male development in the medaka fish

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1968.tb02169.x

Evolution from fish to mammals by gene duplication

Summary A cell line, named Epithelioma papulosum cyprini (EPC) and originating from carp epidermal herpes virus-induced hyperplastic lesions, was esta blished and has now given rise to more than 80 subcultures. It grows within a wide temperature range (15–33°C), survives between 7 and 10°C for several months without alterations in its further virus susceptibility and growth characteristics, and degenerates at 37°C. Its karyotype is 2n=96. It propagates most of the systemic infection viruses of the fish families Salmonidae, Cyprinidae, Anguillidae and Esocidae, as well as Indiana-type vesicular stomatitis virus. Despite the origin of EPC cells, we were unable to demonstrate the presence of herpes virus in them. Their transformation was reflected in their karyotype (normally 2n=100) and by their growth ability in soft agar medium; monolayer growth, however, was inhibited at a density of 3×106 cells/cm2. The temperature growth range, good splitting ratio (1/10) and virus susceptibility make EPC cells a highly suitable material both for fish pathology and for comparative virology studies.

Some properties of the Epithelioma papulosum cyprini (EPC) cell line from carp cyprinus carpio

Polyploid fish and shellfish: Production, biology and applications to aquaculture for performance improvement and genetic containment

Fin-culture was achieved in the medaka, Oryzias latipes, and detailed karyotype analyses were undertaken by differential C-banding and silver staining techniques. Wild and orange-redvarieties of the medaka showed the same karyotype characterized by 48 chromosomes consisting of 2 pairs of metacentrics, 8 pairs of submetacentrics, 1 pair of subtelocentrics, 13 pairs of acrocentrics (FN=68). One pair of the smaller submetacentrics showed stalks on their short arms with the appearance of the satellited chromosomes. The latter chromosomes also had NORs on their telomeric or stalk regions of the short arms. No characteristic C-banded chromosome was detected. Centromere regions of almost all chromosomes were C-band-positive. No sexual difference of the chromosomes was detected in the present study.

https://www.jstage.jst.go.jp/article/pjab1977/57/2/57_2_39/_pdf

Detailed and Banding Karyotype Analyses of the Medaka, Oryzias latipes in Cultured Cells

The occurrence of spontaneous polyploid in the Japanese common loach, Misgurnus anguicaudatus.

The chromosomes were studied in five species of cobitiid loaches with the application of current air-drying techniques. It was found that Misgurnus anguillicaudatus, Barbatula toni, Lefua nikkonis and Cobitis delicata had the same diploid number of 50. Comparison of karyotypes revealed the chromosome morphology characteristic of each species. In contrast, Cobitis biwae was remarkable by having 96 chromosomes. No evidence for sexual difference of chromosomes was obtained in the species studied here.

/pdf/a-comparative-karyotype-study-in-several-species-of-japanese-489x256sxb.pdf

Yoshio Ojima

Papers

Detailed and Banding Karyotype Analyses of the Medaka, Oryzias latipes in Cultured Cells

The occurrence of spontaneous polyploid in the Japanese common loach, Misgurnus anguicaudatus.

A comparative karyotype study in several species of japanese loaches (pisces, cobitidae)

A blood culture method for fish chromosomes

Triploidy appeared in the Back-Cross Offspring from Funa-Carp Crossing