fish sex reversal

1. Abhishek Giri

2.  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.  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.  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.  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.  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.  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. 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.  Androgens: 17-α- methyl testosterone
Testosterone
11-keto testosterone
 Estrogens: Estradiol-17-β
Estrone

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