The common carp (Cyprinus carpio) is a fish living in freshwater in Europe, Asia, North America and the Orient in a natural way. The koi carp (Cyprinus carpio carpio) is an ornamental fish native to Asia that derives from the common carp by human selection. In our regions, the koi carp is present in outdoor pools or ponds.
Reproduction takes place between late spring and early summer (between May and July), during the spawning period because at this time the water temperature rises. So the time is quite short!
How to set up the pond for reproduction :
In order to try to have the greatest number of young, it is preferable to use a pond specially designed for reproduction during the spawning period. The pond must be able to hold at least fifteen m3 of water, with a depth of fifty cm to one meter.
Approximately two weeks before the introduction of the individuals for reproduction, it is preferable to clean the pond well. Then leave the pond alone so that it can take care of the small organisms that will feed the carp and fry.
Water quality is an essential parameter to control. The water temperature should be between 18 and 20°C. You can yourself increase the water temperature even if the carps are already present in the pond but you have to do it in a very progressive way to avoid any thermal shock. Among the other physico-chemical parameters of the water, the oxygen level should be about 9 mg/L, the pH should be neutral or slightly basic (between 6.5 and 8.5) and the water hardness should not exceed 15 dgH. In addition, the biological waste of the fish (nitrates, ammonia) must be present in small quantities.
Vegetation is important. In nature, egg laying takes place in shallow water. The female can lay several hundreds of thousands of eggs that will adhere to aquatic plants. It is therefore necessary to decorate the pond with aquatic plants that will serve as a support for the eggs: Water lilies, Canna, Water lily, Freshwater Mint, Iris, Reed, Papyrus, Japanese Reed…It is important to use plants that will be well fixed at the bottom of the pond to protect the eggs.
The parameters of reproduction
In natural environment, what indicates that the carp is able to reproduce is not its age but its size. There is however a range of age of sexual maturity: between three and five years in the female and between two and three years in the male. Thus, for the koi carp, it is considered that they must exceed 30 cm to reach sexual maturity. This corresponds to three years in the female and two years in the male.
In order to reproduce its koi carp in a natural way, it is preferable to have more males than females: approximately 2 to 3 males for a single female.
It is advisable to feed the females well before the reproduction phase so that they have a good body condition.
During the breeding season the males are easily distinguishable from the females. The male is thin and is covered with small outgrowths called wedding buds at the gills, around the eyes and on the pectoral fins. The female has a very swollen abdomen.
Behaviors are different and the fish are excited and chase each other. When the female is located in a fairly dense area of vegetation, she deposits eggs and the male’s seed will then fertilize them: we speak of external fertilization because the male and female gametes meet in the external environment.
How to stimulate reproduction?
It is possible to let nature do its work and therefore to leave males and females together all year round so that they reproduce at their own pace. However, if you want a lot of pups, this method is not the most efficient.
Another way is to separate males and females. Using a special breeding tank as described above, put a single female in the tank and feed her abundantly. Then add about three males in cages in the same basin: this will stimulate the female. The female will quickly rub frequently against the cages containing the males and the males will be agitated. At this point, the cages should be removed and the males left with the female so that fertilization can take place for one or two days. The female will then begin to lay eggs while the males will release their sperm. Then remove the males and let the female finish laying for a few days.
How to manage eggs and fry?
As said before, the carp will lay eggs that will adhere to the aquatic plants and the walls of the pond. This laying lasts about ten days. Once the female has finished laying, the carp must be separated from the eggs because the adults tend to feed on the eggs after the reproduction period (energy requirement). However, if the pond has enough vegetation to protect the eggs, the amount ingested by the adults will be insignificant and you can leave them in the same pond.
The fry hatch in 3 days to a week, depending on the environmental conditions and especially the temperature. The warmer the water, the earlier the hatching will take place.
Once hatched, the newborns can survive a few days on their energy reserve, so it is not necessary to feed them. They then remain attached to the aquatic plants. After two or three days, the fry become accustomed to their environment and begin to swim actively. They also begin to seek food by eating the small microscopic organisms and animals in the water.
You can then start feeding them daphnia as food or another suitable industrial food but be careful not to overload the water.
The fry are only lightly coloured (brown-grey) and will change color in the first four months of life.
The mortality rate is high in the fry, this is why the female carp lays so many eggs. The causes of mortality are malformations, under nutrition or poor water quality. In addition there are many possible predators of the fry: possible other fish in the pond, frogs, birds, cats and adult koi carp that frequently eat the fry smaller than about 3 cm.
This predation ultimately helps to regulate the amount of individuals in the pond that would otherwise be in excess.
Thus, the reproduction of fish is not always easy, especially that of Koi carp. It is important to respect certain conditions and simple rules to optimize the reproduction season of your fish. It is also necessary to be very careful with the climatic conditions (such as the current bad weather) which can have disastrous consequences on the fish, their reproduction and their descendants.