I have been reading about keeping koi and goldfish, in backyard ponds, in order to share the information with my brother. I have found that koi are different in their breeding habits and spawning.
The female koi usually are bred, at 3 years of age and the males are ready to breed at 2 years of age. If allowed to breed sooner the young might turn out to be a poor quality fish. I figure if your planning on selling the young this might be of bigger importance than if their just swimming in your pond.
Then I read that the breeding takes about 20-30 minutes, and it somewhat rough in nature, and you can tell if breeding has accured by the presence of froth or scum on the surface of the water. And that the eggs are translucent and you should be prepared to watch out for them, as the adult koi will often eat their own eggs. Another article I read stated that adult koi have even been noted to eat their own young fry.
After the (spawn) eggs are fertilized with sperm (milt), the hatching of the eggs takes 5-6 days. While in this stage and after hatching is when the baby fry are an easy meal, by their parent koi or by other predators.
My brother was wondering what the breeding cycle was like and why the young fish were disappearing, when the only fish in his pond are American koi. He was upset to learn they eat their young. I thought it was like natures cruel joke. Like "I am alive"! Zip your a meal for daddy.
Anyways, I was wondering if goldfish did the same in their breeding patterns and the eating of their own young? Can anyone tell me more about this so I can share the information with my brother. Is there anyway to prevent this from happening?
His backyard pond is about 8 foot wide by 10 foot long.
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Goldfish & Koi as Pond Pets 
