They are able to absorb oxygen that is in the tiny capillaries that are in the yolk sacuk business email database of their egg. The fry need plenty of oxygen during this stage, or you take a risk of losing all of them. The baby koi have just one posterior fin when they first hatch out. They grow quickly, and develop their vital organs, the rest of their fins, and a mouth fast than you can imagine. At two days old, many of the fry are swimming to the surface in order to fill their swim bladder with air.
At three days, all of the fry should be swimming around in the tank or pond. Feeding Koi Fry Any fry that have developed this far should be ready to eat. Remember that at this point, their taste buds are not mature, and the only way they will know that food is available is to see it floating around them. Most Koi hobbyists use hardboiled egg yolk as the fry’s first food. Brine shrimp are also a fine choice of food for baby koi once they have reached about seven days old.