Will koi and goldfish fight?

M

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Jan 31, 2007
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hello everyone, i have a question about koi and goldfish behavior.

i work at a petstore, and my specialty is aquatics.

the other day at work, i guess "i" sold a guy a koi that would be sharing a space with goldfish. the guy called back a few days later and said that his koi killed all his goldfish. lo and behold, i also found out that the guy put the koi in a 30g tank with his goldfish. if this was indeed me who sold him the fish, i would have never authorized something like that. honestly, we get many customers who lie about their tank anyway because they "know what they're doing." more than anything, i just want to know if koi and goldfish will fight. if they're in that small of a system, i wouldn't doubt them fighting, but i've never seen them fight at work, and we really cram the fish in there sometimes.
thanks for your time
 
It was wrong of you to sell him a koi fish if he wasnt intending to keep it in a pond. A 30g tank is simply not enough for a single koi, let alone a bunch of goldfish and a koi fish. jm1212 is probably right that either the ammonia spike or the cramped conditions killed the rest of the goldies.
 
Sounds like the guy doesnt know how to monitor water conditions, do water changes, and most likely does not have adequate filtration.

Also agree, the koi should not be in an aquarium for very long - they belong in a pond.
 
Any fish can become a bully to other fish. It's basic survival of the fittest... especially in overstocked or undersized tanks. If the goldfish was a fancy goldfish, the koi would have superior mobility and could have easily harassed the goldfish until the fish got so stressed out that it died.
 
is it not even okay to keep a koi in a tank if it is still little? how fast do they grow, lps said an inch a year maybe...but even my goldies grow faster than that, i've had them for 3 months and they've gone from 1" and 1 1/2" to 3 and 4".... i was going to put a koi in my goldie tank....
 
bluekrissyspike said:
is it not even okay to keep a koi in a tank if it is still little?
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Strictly no. They are best kept in the pond regardless of size.
lps said an inch a year maybe...but even my goldies grow faster than that, i've had them for 3 months and they've gone from 1" and 1 1/2" to 3 and 4".... i was going to put a koi in my goldie tank....
Click to expand...
Your lfs is wrong to say that. They grow a lot more than an inch being messy feeders themselves.
 
thanx... i thought that they were wrong....it isn't nice of them to give false info just to sell expensive fish that end up being unhappy..... it just didn't make sense that they would grow so slow when my goldies grow so fast
 
With a varied diet and quality water they grow quite quickly. I started some out in a 20g tank - they were about 2-3" and in 2 months time they were 5-6" so they were growing more than 1" per month. Not only that they were putting on a lot of girth as well - they are all in a pond now; all about 8-9" ...

So if you are not prepared to relocate them in a timely manner, I would not advise starting them out in an tank - if you have arrangements in place, I see no problem with it.
 
IMO the person should have never been told the koi could be kept in any aquarium. Koi and goldfish get along but they need space just like any other fish. If the guy said he had other goldfish I would of asked how many, and what size tank. If he replies anything less than 150g I would not of sold him anything. To get back on the topic, I would agree that it was likley water parameters that killed the fish along with stress of adding the KOI. The Koi could very well of stressed the goldfish as they are faster swimmers and larger stronger fish.
 
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