PPT Slide 1

Dr V.P.Saini Dr V.P.Saini

Prof. & Dean Prof. & Dean

College of Fisheries, Kishanganj

College of Fisheries, Kishanganj

 The expression of sexuality in fishes is greatly diversified, including

 various types of sex chromosomal mechanisms,

 gynogenetic reproduction,

 differentiated and undifferentiated gonochorism synchronous, protandrous and protogynous

hermaphroditism,

 species specific external diversified ethological sexes.

Physiological sex

Physiological sex is formed through

the biochemical process of

ontogenesis under the control of

genetic sex.

Gonadal sex

 The basis of the physiological sex depends upon the type of primary sex organ.

 This basic sex is known as the gonadal sex which is further classified into two groups

 gonochorism and hermaphroditism.

Gonochorism

 Gonochorism is the basic mode of sexuality and the majority fish species express it.

 Separate male and female individuals are involved by the existence of either testes or ovaries in one individual fish.

 In the gonochoristic fishes, there are two types, undifferentiated and differentiated species

 Hermaphroditism is the possession of both ovarian and testicular tissues in the same individual fish

 Protogynous hermaphroditism.

 Protoandrous hermaphroditism.

 Synchronous hermaphroditism

Protogynous hermaphroditism

 First ovary develops and later disappears and male germinal cells appear

 protogynous hermaphrodite fish function first as females then as males by sex reversal at a certain stage of their growth

 E.g. Seabass

Protoandrous hermaphroditism

 Male state differentiates first and ovaries replace the testes by natural sex reversal through a transitory intersexual stage

 Eg. Sparaus spp,Amphiprion sp

Synchronous hermaphroditism

 Both male and female states co-exist functionally, and both eggs and spermatozoa mature at the same time.

 Occasionally found among modern teleost fishes, particularly in family, serranidae, cyprinodontidae

 This is the most uncommon form of hermaphroditism.

Polygenic determination of sex

 Sex determination in fishes is governed by a large number of sex genes that are located on many chromosomes.

 Sex determination in fishes is polyfactorial (polygenic).

 The sex chromosomes carry superior sex genes, i.e., male (M) and female (F) determinants with

greater potencies than those of autosomes

Polygenic determination of sex is of most primitive type.

Sex determination mediated by sex chromosomes

 The sex chromosomes are distinguished from other chromosomes by the presence of sex-chromatin (barr body) and karyotypic difference between two sexes in somatic

metaphase counts.

 This type of sex determination is of more advanced type.

XX♀:XY♂ – system

 Most common system found even in Man

 XX female (homogametic), XYmale(heterogametic) channel catfish, common carp, rainbow trout,

sockeye salmon (Oncorhynchus nerka), etc.

ZZ♂ :WZ♀ – system

 To avoid confusion XY system is omitted

 ZZ male (homogametic),WZ females (heterogametic)

T. aurea, T. hornorum, Gambusia affinis (mosquito fish), Mud skipper

(Boleophthalmus boddaerti), etc

WXY – system

 Y- chromosome produces males except when it is paired with a W chromosome

 The W chromosome is a modified X chromosome that blocks the male

determining function of the Y chromosome

 reported in platy Xiphophorus maculatus

Multiple sex chromosomes

 X₁ X₂ X₂ – females, X₁ X₂ Y– males Eg.,Cyprinodon sp.

 ZZ / ZW₁ W₂ . Multipe W chromosomes are present. ZZ– males, ZW₁ W₂ –

females Eg. Apareiodon affinis

 XY₁ Y₂ males, XX – females.

Eg. Hoplias sp.

 In this system the number of

chromosomes is not constant within a species.

Autosomal sex-determination

 Sex determination is not controlled by sex chromosomes

 Some species of fish do not have sex chromosomes

 In these species, sex is determined by the number of male or female genes that are located on the autosomes.

 E.g. Limia

Atypical sex determination

 They share the phenomenon of incomplete penetrance, i.e., individuals with the same genotype for atypical sex determination may develop into either male or female.

 The phenomenon of atypical sex determination has a genetic basis and each instance is caused by the interaction of an autosomal factor with a specific sex chromosome

Metagamic sex determination

 Nutritional or other effects of crowding and competition induced development into males, which mature at a much smaller size than females

 Environmental factors such as temperature, photoperiod, salinity and even crowding can help to determine sex in fish

Contd….

 There is a possibility that pH of water during reproduction may influence sex ratio.

 Pelvicachromis and Apistogramma, sex ratios are strongly biased toward females in basic water and toward males in acid water

Secondary sexual characteristics

 Relate to courtship and other aspects of mating, develop after sex differentiation and can be permanent or temporary

attributes of fish.

 Secondary sexual characteristics seem to be controlled by steroid hormone

produced in the gonads.

 The secondary characteristics are of very significant economic importance.

 The brilliance of colour patterns and elegance of fin extensions are of obvious value to the ornamental fish breeders whilst growth rate is of considerable interest to fish farmers

 For these reasons, the control of sex ratio and of sexuality itself are important in fish genetics

Sex Chromosomes and Colour Patterns

 the zebrafish, Danio rerio, has environmental or polygenic sex determination without heterosomes;

 the southern platyfish, Xiphophorus maculatus, which has genetically defined sex chromosomes; and

 the guppy, in which the acrocentric Y chromosome can be identified cytogenetically.

Thank you