Goldfish & Koi as Pond Pets

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.

Both Koi and Goldfish will eat their eggs if given the chance, to them it's just an extra food source.
Firstly it is not a good idea to try to keep koi in a pool (pond) designed for goldfish. Many pond keepers want a combination of pond plants, lillies, oxygenators and marginals to decorate the pond and keep the water quality in good balance. To this can be added a selection of goldfish, fancy goldfish (fantails etc.) and shubunkins.
Koi are fish that are capable of growing to up to a metre in length and would in a very short space of time decimate a pond of it's plant life by ripping it up and eating much of it, leading to the pond losing it's ecological balance and becoming a horrible green stagnant eyesore.
From the breeding point of view if the pond is well stocked with oxygenators and floating plants (water chesnut) goldfish will chase the females en masse into the plants to release her eggs and the males eject their milt (sperm) to fertilise them.
They will also try to eat them but as a general rule if the pond is well planted some will survive to hatch and hide in the plants until they are large enough to survive.
Many hobbyists involved in the showing of fish will transfer the plants, with eggs attached, to a nursery pond to hatch so they can rear a high porportion of the spawning.

As a follow on to the above, koi are generally kept in a koi specific pool, although people do try to keep them in goldfish ponds and if introduced into a mature pond at around 4" can appear to settle without a problem. Until they start to get bigger and bigger.
A koi specific pool would be a large pool devoid of plants with bottom drains and heavy external filtration, Many people off-set the pool's barren look by creating a japanese garden around it with walkways, japanese specific plants and tubs and sometimes a bridge.
Koi, certainly in the UK, are not that easy to breed. Where goldfish tend to spawn naturally as the water warms up koi quite often need an inducement.
Most serious breeders will keep a spawning pond and as the females become plump with eggs will tranfer one female and two males into the pond which will have had artificial spawning mats introduced for the fish to spawn in.
Spawning is induced by a large water change which will drop the temperature a couple of degrees and usually kick starts the whole process. The fish are watched the whole time by the breeder as the whole process can become very aggressive risking major damage to the female. Once completed the fish are quickly netted and transfered back to the main pool to avoid too much egg eating.
Koi like most fish can be hand spawned, or stripped, and the eggs and milt mixed to ensure maximum fertilisation, but this should only be undertaken by an expert or the fish could be badly injured.

When I was young, my father really enjoyed keeping koi. We had a garden pond which was about 8 ft by 10 ft and was about 2 ft deep. This was in Malaysia where water temperatures during the day can reach between 24 and 26 degrees Celsius. Our pond was shaded by a lot of trees to avoid exposing the fish to too much sun as well as to shield the smaller fry from attack by tropical kingfishers.

We had a mix of gosanke, shusui, tancho, kinginrin and a few bekko.

When we bred our koi (usually the gosanke) we would buy large bundles of raffia strings which we would tie together to make large raffia mops. The breeding pairs (usually we would use a ratio of 2 males to one female) would be placed in a large fiberglass tank. Once the fish have spawned (quite noisily as the males chased the females, bumping against the tank and they would sometimes hit them violently to make them expel the eggs) the sticky eggs would stick to the raffia mops. We quickly remove the fish and so the eggs would be left in peace. The raffia mops mimic the function of water plants and also help to hide the eggs from the hungry parents. I'll try to find some photos of the raffia mops so I can post them later.

Well the best way to keep this from happening would be to separate the babies from the parents. The best way I would think of doing this would be to set up a 55 gallon aquarium inside, and then transfer the eggs/babies there and wait for them to grow a little bit. And then once they gain some size, you can move them back into the pond. I don't know what percentage of the eggs end up hatching because its probably better if you let the eggs hatch where they were laid versus moving them, however, if they eat a lot of the eggs, you may want to just move the eggs. Either way, best of luck!

How do you take care of the fish in the winter time? Do you need to bring them indoors during the winter months then transfer them back outdoors during the summer months? I've always wondered this about places with outdoor Koi ponds. Or do they swim around under the ice in the water? How do they get any food if that is the case?