Snakefish

Snakefish, the only sapient fish to appear in the Redwall series, was a massive eel who lived in the Toadlands. He had a ravenous appitite for toadflesh, which inspired him to relocate to the Toadlands. Eventually, however, Snakefish was captured when he fell into a trap laid by the toads of Marshgreen, and he was thrown into the Screamhole.

The toads used him to eat their prisoners. Later, when Martin the Warrior, Young Dinny, Log-a-Log Big Club, and Gonff the Mousethief were captured and tossed into the Screamhole, he joined forces with them long enough to escape and revenge himself upon the toads. fr:Serpenda