Originally Posted by tadpole
I have a young and very colorful Corn Snake that lives in my Pond environment. They have much the same diet as Water Snakes. They like small fish (along with frogs, tadpoles, salamanders etc.) and will not attempt to snare anything as large as a Koi, except maybe when the Koi are very young fry. They eat their prey while it is still alive. No way they can handle a Koi. They are also great for rodent control when they grow to adulthood.
If something is getting your Koi, you can bet that it is not a snake.
not saying thats it, sure it depends on the size of each animal. I would think a 8 or 10in fish is possible with a 4 ft snake. But of course...no way with a big 2lb fish. What size koi are we talking about?