Brown water snakes are reported to eat vast quantities of catfish (percent wise). And to a lesser extent other benthic fish. Mine are very young and are fed rosy reds and goldfish. I have few options at the present to eliminate the goldfish altogether. I offered them trout strips with no interest, for the time being, however that snake may have been in the last stage of it's shed cycle. I'm going to try again shortly. Best luck.