Are Koi and goldfish related? - Quora

Is it safe to assume that Koi and Goldfish are similar to each other in regards to hardiness?
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What I'm tempted to do is throw a bunch of goldfish in my systems to start with simply because they are a lot cheaper, and then maybe add some koi a few months down the line so long as my system is all running fine.

What do Koi and goldfish eat? Can either/both of them eat duckweed? They are omnivores right?
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were developed in more than a thousand years ago by Prussian carp for color . By the (960–1279), yellow, orange, white, and red-and-white colorations had been developed. Goldfish () and () are now considered different species. Goldfish were introduced to Japan in the 16th century and to Europe in the 17th century. Koi, though, were developed from common carp in Japan in the 1820s. Koi are domesticated common carp () that are selected or culled for color; they are not a different species, but a subspecies, and will revert to the original coloration within a few generations if allowed to breed freely. Koi and Goldfish will interbreed but it is more likely that the fry in question are goldfish.
Photo provided by FlickrFish expert Robyn Rhudy raises koi and goldfish and says the major differences between the two are size and cost.
Photo provided by FlickrI have a batch of fry, I swear some are koi, some are definately goldfish and others are a mystery to me.
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Two species of carp are often kept in ponds and larger home aquariums. Both are Asian in origin and appear superficially similar. Goldfish are actually descended from crucian carp, while the koi have barbels, grow longer, and are in fact a fancy domesticated version of the common carp. Although more widely known in the wild, the koi fancy is more “elite” than the goldfish scene, with millions of dollars being invested in the finest fish.Unfortunately, koi are boisterous and have a habit of jumping. This can result in their death in a pond setting, while feral carp may injure boaters as they jump. Both goldfish and koi are technically edible, but their popularity as food is especially limited in the Western world. Neither fish have true teeth, so hand-feeding any size of specimen is safe. Their throat plates serve as crushers to mash up food prior to swallowing.Koi and goldfish have the potential to become invasive species when introduced to non-native waters. Results may include vegetation damage and predation of native species. Koi make excellent pets, and will put their head out of the water to collect food from their owners. Goldfish are perhaps less intelligent and sociable, but both species of carp can easily be tamed and enjoyed. Goldfish should never be placed in a bowl. A proper tank must be offered to prevent ammonia buildup and ensure adequate room for exercise and swimming development.While goldfish and koi are very different and quite distantly related, it can be difficult for the uninitiated to tell the difference between the two. However, it is not difficult to tell koi from goldfish once you know what you’re looking for.Although goldfish and koi carp are sometimes kept together in the same pond, and are related, the two types of fish are actually different species.Koi carp are unlikely to eat other large fish, including large goldfish. However, if something will fit in their mouths then they may well try to eat it! So smaller goldfish will be at risk.