The concerns of the other poster are still relevant, when camping this mob I found that a handful of fish somehow got stuck in the wall underneath the world by the zone entrance. If you're having trouble spawning him, it would be worth clearing all of the fish you can see and then bring a tracker to confirm that no other fish are alive.
Spawns in the large pool with many fish in the south eastern part of the zone, location is 122, -176, -260 approx.
Spawn rate is uber rare, I was here for 36 hours before he spawned. Dropped the club. Happy hunting.