Hi Jim, I haven't done it myself but I've asked the same question a bit earlier in this forum and it seems that yes, tilapia and koi can live in the same tank. I was told that catfishes can also be added... 3 species in the same tank is kinda nice :)
I have both Koi and Tilapia in my large tank and they have been coexisting with no issues for about 8 months. I use Koi from my small pond to cycle my tanks (I'm one of the few who does not practice fishless cycling these days).
I participate in a few of the Aussie forums - there are several others in Asia and Canada who successfully mix the two as well (Tilapia are illegal in Australia).
My plan was always to move the Koi out...but I ran out of room as the Tilapia multiplied. Now I'm kind of attached to them. They are very friendly fish, especially when you've got food for them. Anyway, absolutely no worries mixing the two.
Chip is right, the catfish can pick off the small fry offspring of other fish, and since Tilapia are cichlids, they can have an aggressive temperment, I havent owned them yet, but the cichlids that I have owned, can be very agressive. Sometimes it depends on how you introduce them into the environment, but I could easily see a cichlid eating a goldfish that is much smaller.
It's interesting, because I've have various cichlids over the years - oscars, convicts, peacock bass, etc. I think overall, the Tilalpia are much easier on their tankmates. When they start the breeding games, the males can get a little rough but I've never had a fish injured (knock on wood). Living in Thailand, of course mosquitos are an issue. I keep "guppies" in my pond, along with the Koi and Tilapia. Believe it or not, they seem to do ok together. I'm sure the guppy fry don't last long, but the adults do great and really help as they love to eat mosquito larvae. I would be cautious but I'm thinking all but very small goldfish would be ok. Tilapia really aren't the big predators that some of their cousins are. Their natural diet leans much heavier towards vegetation. Of course most fish are opportunistic and Tilapia will eat live food, so just be careful if you're attached to the goldies.
I have one talapia tank and one koi smaller pond that also has some kind of wild smaller fish like killies or mimmos that are multiplying too much if I put some in the talapia tank would they be food for the bigger fish because the koi don't eat them and they are taking over the koi pond? Thanks for all your input
Thank you for the post :) I've done a similar thing (Started with goldfish, then added a few koi). I've been interested in adding a couple catfish to my FT too. It sounds like some people have had success in doing so, so I think I'll have to try it! Since catfish can be fairly predatory, I would imagine it may be a good idea to buy them smaller than my goldfish/koi if I can, any thoughts?
I added 2 small tilapia to my 250 which currently has 12 large goldfish. This was a test to see if they could coexist in a large tank where crowding wasnt an issue. For a week or so everything was calm. During the second week I started noticing some fin damage on the goldfish. This came to an end when I woke up to find 2 of the goldfish badly hurt on the surface. Both goldfish subsequently died and the 2 tilapia were moved back to the general population.