If you just noticed that your pond now has a million little koi fry swimming around then skip down to the feeding section but if you haven’t bred koi yet and need an introduction then read on. Spawning typically occurs in the early summer months and is very water temperature dependent – 68 degrees F is the minimum for spawning . Your adult koi will have to be sexually mature to engage in successful mating and this typically occurs at age 2 for males and at age 3 for females. Keep in mind when you are selecting the parents that the larger the female, the more eggs she can produce. If you are wondering about how to tell the sex of your koi, there are different approaches to this such as looking at pectoral fin shape and size but the tried and true method is to inspect the underside of your koi. If there is one vent (slit) then you have a male, if you have two vents (slits) then you have a female. Usually spawning activity, and the behaviors associated with it, will take place in the early morning and may only last 30 minutes. The whole process is a bit rough as the male needs to physically stimulate the eggs to be released by nudging the female’s belly. After eggs are released, the male fertilizes them by releasing sperm.
If you plan on having a dedicated spawning tank you will most certainly want breeding material. This is simply material that offers surface area for the eggs to stick to. This could take the shape of aquatic plants, ropes, a “spawning brush” or a “spawning mop”. Most importantly it needs to be something that won’t be toxic in any way and has lots of surface area for eggs to attach. You will want to have plenty of breeding material for the eggs to attach to-maybe around 50 to 60 percent of the bottom of the spawning tank should be covered. The size of your spawning tank will depend on how many fish you plan on trying to get to reproduce. It should be something on the order of 1 to 2 feet deep and maybe 6 feet by 6 feet –some hobbyists have used inflatable kiddie pools with success. After eggs have been laid and adults removed from spawning tank you should see hatching around 4 days later. When you are satisfied with the density of hatched fish you can remove the breeding material. So what will the eggs look like? See below.
You may choose not to go with a separate fry tank or pond and simply let it happen in the main pond. If this is the case be aware that if you have goldfish amongst your adult koi you will have some egg loss due to the goldfish’s appetite for koi eggs. Your koi eggs will hatch around 4 days after they are fertilized. They will then attach themselves to structure like the side of the tank or pond for 2-3 days where they will be feeding off their yolk sac. If you are seeing a great deal of swimming koi fry and also a lot of eggs at the bottom feel free to remove those as they most likely failed to fertilize and will only drive ammonia levels up. Be sure to monitor all your water chemistry, especially ammonia and pH.
What to feed your koi fry?
At around the 10th day (sooner depending on water temp) you will notice your koi fry trying out their new-found ability to swim and it’s at that time that feeding should begin. A lot of koi enthusiasts will start off with something called “infusoria” which is not a thing but more of a size classification. Generally, it’s defined as very small aquatic organisms and for koi fry those should be live daphnia (water fleas) and/or brine shrimp (“sea monkies”). If you can’t obtain infusoria you can try chicken eggs. Boil the eggs (some just use the yolks) and, in a blender, mix with about 30 or so ounces of water from the tank or pond. Simply squirt that mixture over the surface of your breeding tank or pond. You will want to feed around 4 times per day. In general you are trying to match the size of the food with the koi fry such that it is an appropriate size for them to eat. After about a week of this mixture you can switch to a powder called “fry powder” which can be sprinkled over the water’s surface. You can also use standard protein infused koi pellets and basically grind them up into a fine powder and select for a certain grain size by shaking it through a sieve. It may take a few days for the fry to associate the new powder with food and acquire a taste for it. Be sure to clean the bottom of the tank for any waste and excess/uneaten food –you really want to avoid ammonia build up. Make sure that you provide plenty of aeration for your koi fry and this is especially true in the summer when warmer water temps mean less oxygen carrying capacity of water. Some other foods that you can feed are frozen brine shrimp, growing live brine shimp in your containment tank or main pond and freeze-dried krill. You may also add, as a nutritional supplement, spirulina powder and wheat germ.
One mistake people make is trying to keep all the koi fry, that’s a bad idea. You definitely want to “thin out the herd” because by doing so you create a more healthy environment for the remaining koi. Your first round of culling should take place at around 1 inch or 25mm. This should fall at about 4 weeks (possibly longer) after swimming is first observed. Another culling should take place a month after the first or about when they are about 2.5 inches or 6.25cm. The first and second culling should remove about 80% of the initial population. Additionally, a third culling should start a month after the second one and remove 50 to 60% of what’s left (see the “Breeding Timeline” below). When culling you should be looking for deformities, undesirable coloration, erratic swimming, sluggish swimmers and generally undesirable traits. You don’t necessarily have to euthanize these fish-give some to your friends!
When your koi do finally make it to a larger size and you want to introduce them to the main pond be aware that adult koi will eat most anything and the baby koi might be on the menu if they are small enough. Be sure to release them only when they are big enough that they won’t actually fit in the adults mouths!