Many of the Natricines (watersnakes, gartersnakes, etc) will eat fish. Some of them will eat nothing else. There are a variety of other types of snakes that will eat fish as well.
not just because im taken by a cool eater, but also because fish are cheaper and i assume safer(live) than store mice. any information would be great!
I don't know that feeding fish is a better alternative to feeding mice. Feeder fish are bred in large outdoor ponds and these feeders often have pretty high parasite loads due to the overcrowded conditions of their ponds. Lab rodents are bred in much more hygenic conditions with less exposure to environmental contaminants and parasites.
You can feed frozen fillets or whole fish of certain species except that some species produce an enzyme called thiaminase which breaks down the vitamin B in the fish. Therefore the snakes could get a vitamin B deficiency. Some species of fish don't have this problem. Do some research online and you should be able to find out which species of fish are OK.
The other thing about feeding fish is the smell. There is nothing more putrid than the smell of snake feces from a fish eating snake!
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Chris Harrison
San Antonio, Texas