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

Acknowledgments.-The authors would like to

Sex control and manipulation in fish

Among vertebrates there is wide variation in the degree to which sexual differentiation is developmentally buffered, or canalized. In birds, and particularly in mammals, gonadogenesis occurs early in development and without a significant contribution from the environment. In contrast, sexual development in teleosts is protracted and plastic. Here I consider this lability in the context of the developmental processes underlying sex differentiation in teleosts, and contrast these processes with those in other vertebrate taxa. One fundamental difference in teleost sexual differentiation from that of letrapods may be in the developmental polarity of the brain-pituitary-gonadal axis. In mammals the gonads differentiate early and affect, through the release of steroid hormones, the sexual differentiation of the brain. It is proposed here that in teleosts the brain is the initial site of sexual differentiation, and that the pattern of differentiation in the brain determines the fate of the gonads.

Sexual Lability in Teleosts: Developmental Factors

Many species of fish produced in aquaculture or for the ornamental fish trade exhibit sexual dimorphism in growth, age at maturity, secondary sexual characters, or other traits of interest. This has led to a desire to produce populations of only one sex for commercial ongrowing. Although direct sex reversal via manipulation of sex differentiation is used commercially (e.g., in tilapia aquaculture), in most cases there is a need to understand the sex determination system to some extent and manipulate this to produce monosex fish. Sex determination is the genetic or environmental process that establishes the sex (gender) of an organism, whereas sex differentiation is the process by which an undifferentiated gonad is transformed into an ovary or a testis. Fish are the most diverse group of vertebrates in terms of sex determination, and the number of fish species of interest to aquaculture keeps increasing. Together, these aspects explain the growing interest to understand how sex determination and differenti...

Fish Gonadogenesis. Part I: Genetic and Environmental Mechanisms of Sex Determination

Teleostean fishes constitute a proliferous evolutionary grade, which shows a correspondingly diverse array of sex-mechanisms. Although most species are gonochorists, many groups have independently evolved monoecy as a response to varying degrees of breeding isolation. On the other hand, cytologically expressed heterogamety distinguishes several groups, especially those represented by the deep-sea species investigated, which belong to primitive and intermediate orders. Acetic-orcein squashes of kidney, spleen, and gonad reveal heteromorphic chromosome pairs in males of nearly half the 25 species of deep-sea teleosts examined. Within one family, the Y chromosome varies interspecifically in size from the second largest to the smallest element in the complement. Most such pairs are identifiable as atypically behaving bivalents associated end-to-end; some of these, perhaps, are expressed as heterochromatic bodies in preleptotene. The dimorphic components segregate in the secondary spermatocytes. Two k...

T. R. Chen

Papers

Heterogamety in Teleostean Fishes