These ornamental fish show gender dimorphism. The adult males and females can be distinguished by the intensity of color, size and the presence or absence of gonopodium.
Ornamental platy fish are livebearers and they give birth to young babies after a gestation period. Gender differentiation starts in ornamental platy from the second month of age.
These ornamental fish become reproductively active from 3rd month of age. The males will start following and chasing females to mate. Given the right feed, temperatures, pH and water hardness the breeding is a continuous process throughout the year in these ornamental fish.
Male ornamental platy
Immature male and female ornamental fish are indistinguishable and may also have dull coloration. The gender of these ornamental fish becomes distinguishable when they are nearing maturity.
From the second month onwards this ornamental male fish starts to undergo maturation with physiological changes from within with the development of gonads.Externally the color pattern of the male fish undergo changes and vivid colors specific to the strains are developed.
In these ornamental male fish, simultaneously, the formation of reproductive parts starts externally. The normal shape of the anal fin of the ornamental male fish will start to undergoing changes.
It gets modified into an intromittent organ. The 3rd, 4th and 5th anal fin rays in the male fish will form into a tubular structure called gonopodium. Soon the gonopodium in the ornamental male fish become movable and can be kept in an ‘erect’ position pointing forward and towards the female during mating.
The male ornamental fish briefly inserts the gonopodium into the female genital opening and inserts spermatophore. The spermatophore is a capsule containing closely packed spermatozoa.
Female ornamental platy fish
The female siblings of a brood show faster growth rate and after 2nd month they are apparently bigger in size than their male siblings. The ornamental female platy starts to have reproductive maturation from the end of second month.
The ovaries start to grow and mature. The ovaries will start producing eggs. The genital opening undergoes changes to receive spermatophore to become pregnant.
Ornamental female platy fish may become reproductively active from the third month onwards. When the female is fully mature and when a male approaches, it becomes responsive and stays still or moves slowly in a circle.
It allows the male to come closer and allows the male to mate and deposit the spermatophore into its genital opening. With this action of male, it becomes pregnant; the eggs in the female get fertilised and start to develop into a embryo.
It has been found that males appear to prefer larger females. The males also are found to sneak mate without male courtship.
Pregnant ornamental platy fish
Pregnant female is a unique stage in the livebearers among the fish. Unlike most of the other fishes, the female livebearers go through the pregnant stage by retain the fertilised eggs inside their body for the growth of embryo and give birth to free-swimming babies.
With the development of ovary and formation of eggs, the abdomen region of the female platy starts to appear bulky and pregnant. When the male platy deposits the spermatophore into the mature female the eggs soon get fertilised and female becomes ‘pregnant’.
Most of the required nutrients are already packed in the eggs before fertilisation. Ornamental pregnant platy has only single stage embryos in their ovary at a given time.
The embryos develop inside the body of pregnant platy inside the eggs and the unborn babies are nourished by the egg yolk present in the eggs. There is no placental connection or supply of nourishment from the pregnant mother.
However the body of pregnant mother platy provides for gas exchange (for the respiration of embryo). Externally, if the pregnant platy is of light colors, initially a small gravid spot, as a black pigment spot appears closer to the anal fin of the pregnant fish.
With time the abdomen and the gravid spot enlarge in the pregnant ornamental fish. In dark colored ornamental pregnant fish the gravid spot may not be visible.
The gestation period in pregnant platy varies between 30 to 40 days. Close to parturition the pregnant female is heavy with her abdomen and slow in movement. This indicates that the pregnant platy is about to give birth.
The pregnant female may go to a secluded hiding place to drop its babies.
It has been found that in nature the pregnant ornamental fish after giving birth to babies does not feed for a few hours due to hormonal effects of parturition.
This is the time you shift the exhausted ‘pregnant’ female from the babies as later it may start feeding on the babies. The ornamental fish can become again pregnant without male with the use of sperms already stored.