The Development of Koi Fry
Koi is easy to breed therefore most koi owners breed their own koi. Koi breeding should be done in a separate tank or section of the pond separated by a breeding net. When koi eggs are hatched and fertilized, the eggs are transparent and very sticky. The best way to catch the eggs is by using a spawning rope. This is also the ideal place for the koi fry to hide under and attach to when they first hatch. After the eggs are laid, you will see black dots in them which are the koi’s eyes as they begin to develop. Koi eggs typically take about 2 days to hatch.
When koi fries are hatched from their eggs, they cannot swim and so they attach themselves to the side of the pond or the edges of the spawning ropes through a special sticky pad on their heads. They also do not have any taste buds yet and can only detect food by sight alone. But neither do they have mouths or swim bladders so you should not feed them yet. It is important to ensure the breeding tank is well aerated otherwise many of your koi fry will die because their respiratory system is not fully developed yet. As they grow, the koi fry develop mouths, gills, fins and other vital organs. After 3 or 4 days, they would be able to swim. This is when you should start feeding them.
Once all the fertilized eggs have hatched, you should remove the unfertilized ones so as to prevent them from decomposing and producing ammonia, which may destroy your entire stock of koi fry. Koi fry can be fed with hard boiled egg, infusoria (a combination of single-celled algae and tiny aquatic creatures) or daphnia (a type of crustacean found in ponds). You can either collect your own infusoria and daphnia or grow them yourself.
By the time they are 3 or 4 weeks old, the koi fries would be about 1/4 to 1/2″ in size. At this point, they can be fed newly-hatched brine shrimp and eventually regular koi pellets as they continue to grow. But avoid feeding them these koi pellets or other commercially produced foods until they are at least 6 weeks old as these foods may damage their gills.
When the koi fries are 6 weeks old, it is time to cull them. By this time, you can spot deformities and other defects in your koi fries. Those with such features should be culled.
Koi fish would continue to grow until about 15 to 20 years after which they are considered adult koi. The average lifespan of koi is about 50 years. This is what makes koi keeping such a fulfilling hobby. You can watch your beloved koi grow and provide you with decades of enjoyment.