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SEX REVERSAL

Sex reversal in fishes

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SEX REVERSAL

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  1. SEX REVERSAL&ROLE OF STEROIDSIN SEX REVERSAL AbhishekGiri

  2. CONTENTS • Introduction. • What is sex and sex reversal. • Biological effect of sex reversal. • Temperature induced sex reversal. • Approaches of hormone treatment for sex reversal. • Methods of hormone treatment. • Example of steroid hormone. • Treatment with steroid hormone. • Conclusion. • References.

  3. Introduction • In the early stage, the gonad’s have undifferentiated tissue which can differentiate into both testis and ovary. • Hormones are responsible for natural differentiation of testis and ovary in the two sexes. • Sex reversal in fish has been achieved both ways: from male to female and from female to male. • Yamamoto (1953,1955) showed the importance of sex reversal for studying sex determination mechanism in fishes.

  4. What is sex and sex reversal • Genetic sex is the balance between androgens and estrogens may determine which gonadal sex develops. • Total functional sex reversal can be induced in a number of gonochorists, if environmental or chemical factors are applied before the phenotypic sex has been defined.

  5. Biological effects of sex reversal • Steroid hormone treatment increase mortality in a fish population. • Androgen treatment during sex reversal enhance growth rate in several species of cyprinids and cichilds. • High dose or long duration of steroid hormone treatment inhibits normal gonadal development. • High dose of androgen treatment sometimes led to production of females in lieu of males (Paradoxical sex reversal).

  6. Temperature induced sex reversal • Thermal liability of sex differentiation was demonstrated in some teleosts. • 100% females were obtained in the atherinid fish when juveniles were transferred to colder temperature of 13-19℃. • 100% males were obtained when they were transferred in a warmer temperature of 29℃. • Temperature induced sex reversal may prove more advantageous than hormonal approaches because it will be easier to practice.

  7. Approaches of hormone treatment • Direct approach : monosex population produced directly by hormone treatment. • Indirect approach : by this approach a monosex population can be obtained in two steps. • First a broodstock population is established by sex reversal. • Then these sex reversed individuals should be bred to produce monosex population.

  8. Methods of hormone treatment 1.Dietary supplementation: The hormone mixed feed is the most widely used and the easiest method for achieving sex reversal. 2. Immersion technique: juvenile fishes are immersed in hormone treated water. 3. Injection : Injection requires less amount of hormone to cause sex reversal. It is very much laborious and expensive.

  9. Example of steroid hormone • Androgens: 17-α- methyl testosterone Testosterone 11-keto testosterone • Estrogens: Estradiol-17-β Estrone

  10. Treatment with steroid hormone • Androgens and estrogens are considered to be the natural sex-inducers. • It has been known that treatment with steroid hormones can cause a change in the gonadal sex in fish. • The ability to control sex in fish is of high importance in aquaculture.

  11. Paradoxical feminization : when treating fish with testosterone (T) or MT either at high doses or over extended periods, often a paradoxical feminizing effect of these androgens can be observed. • Sensitive period: Many gonochorist fish species are particularly susceptible to the action of exogenous steroids or environmental factors that influence the direction of sexual differentiation during a certain sensitive period.

  12. Conclusion • The goal of sex control differs from species to species. • Before making any effort for the development of sex control technology, it is essential to consider the biological characteristics of the species. • For successful sex reversal, the timing, dosages and the method of hormone treatment should be standardized. • While applying the sex reversal technology for the commercial scale culture, effective population size should be taken into consideration.

  13. References • Applied fish genetics : B.K.Padhi and R.K.Mandal. • A text of fishery science and Indian Fisheries : C.B.L.Srivastava. • Internet.

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