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Fish keeper here. As best I can tell, there are no koi in this photo. Those are all tilapia. There are no exotic fish or even catfish in this pic. Sorry to be pedantic.
Tilapia are common food fish that grow (and eat) very quickly. They do well in warm water and will out-compete most other fish in situations like this. You can’t easily stock ponds of tilapia with other fish.
What I’m getting at is that if there are any koi in this pond, they would get virtually no food and be out-bred and out-eaten by faster/more voracious generations of tilapia. Koi also prefer cold, clean water and take much longer to reach breeding size. This looks like warm, still water. Koi aren’t great at hunting down bug larva, tilapia are. Which makes sense as to why they were added to combat insects.
Also under stocking levels such as this, and assuming floating fish food, I can be fairly certain that this pond doesn’t contain many (if any) catfish at the lower depths. There wouldn’t be much food reaching them at the bottom and in warm months oxygen depletion would probably kill them. I suppose catfish could scavenge dead fish, but tilapia are omnivores and would probably eat most of the carcasses themselves.
**tl/dr: These are tilapia, which are neither exotic nor catfish.**
Amazing pic and the perfect fish to deal with the insect problem. You can even eat them.