Safe size difference?

[SimonW]

Hello friends:

Due to convenience I moved some small koi (born summer 2021, 7-10 cm) together with my bigger koi (mostly 35-65 cm) into the pond. After I made the murky water clear several days later I found that many of the small koi have disappeared. Then today I witnessed that at least 1 bigger koi (about 45 cm) was chasing the remaining small ones. I had been wondering why the big koi were dashing around in the pond without "obvious" reasons! So I guess that it is not just magpie (a magpie have taken quite a few small koi from the tank I used to keep small koi that I wanted to get rid of) but also big koi love to eat small ones.

So I wonder what the safe size difference is. My best small koi are in a separate big swimming pool right now, but when the winter comes it would be much easier to over-wintering them if I can keep them in the same tank as the big ones.

Thanks for your thoughts!

[socalaker]

Hello friends:

Due to convenience I moved some small koi (born summer 2021, 7-10 cm) together with my bigger koi (mostly 35-65 cm) into the pond. After I made the murky water clear several days later I found that many of the small koi have disappeared. Then today I witnessed that at least 1 bigger koi (about 45 cm) was chasing the remaining small ones. I had been wondering why the big koi were dashing around in the pond without "obvious" reasons! So I guess that it is not just magpie (a magpie have taken quite a few small koi from the tank I used to keep small koi that I wanted to get rid of) but also big koi love to eat small ones.

So I wonder what the safe size difference is. My best small koi are in a separate big swimming pool right now, but when the winter comes it would be much easier to over-wintering them if I can keep them in the same tank as the big ones.

Thanks for your thoughts!

I see koi eat a couple of inch’s minor - when you don’t feed them for a while. Otherwise they don’t bother to eat live fish since it cost too much energy to chase them.

[NaturalK]

Usually after around 10cm or so, koi stop eating each other. I've kept my 50cm koi with my 8cm koi time after time. Most likely they went into your filter or a pump, honestly. At least that's for me, and I feed my koi a lot. Large koi generally do not eat other fish ever, really.

[Matt24]

That sounds surprising to me Simon. I've put 2.5" (6-7 cm) young in with 30+" (76 cm) adults with no problem. I do add some cover for a hiding place, just to make them feel more secure, not because I think they'll be eaten. I've used a large plastic planter box turned upside down with large openings and rocks tied to it to weight it down. It reminds me of a garage with little koi parked in it.

Your situation could be something like what I have noticed with both koi and chickens. If you feed them something delicious but new, they may ignore it. But in due time, if one takes a taste, they realize they love it and start attacking it with enthusiasm, and the others quickly catch on. Maybe your big koi slurped one in a little one by accident, and everything changed.

This also ties into a theory about shark behavior, but I'll stop there ...

[SimonW]

That sounds surprising to me Simon. I've put 2.5" (6-7 cm) young in with 30+" (76 cm) adults with no problem. I do add some cover for a hiding place, just to make them feel more secure, not because I think they'll be eaten. I've used a large plastic planter box turned upside down with large openings and rocks tied to it to weight it down. It reminds me of a garage with little koi parked in it.

Your situation could be something like what I have noticed with both koi and chickens. If you feed them something delicious but new, they may ignore it. But in due time, if one takes a taste, they realize they love it and start attacking it with enthusiasm, and the others quickly catch on. Maybe your big koi slurped one in a little one by accident, and everything changed.

This also ties into a theory about shark behavior, but I'll stop there ...

The chase seems to have calmed down. As you and NaturalK wrote koi are not aggressive. They have at least not chasing the golden orfe fry in the same pond.