Thailand's giant stingrays and the whip rays of Australia can grow up to 16 feet and 1,300 lbs.

Wolf fish, known locally as haimara, can reach a metre in length and is said to hunt humans.

There's a freshwater fish with a shock five times more powerful than a US wall socket.

The Thai snakehead is said to be able to move on land, and has apparently spread to US waters.

In Nicaragua, Zeb faces his most difficult battle hunting for one of the biggest monsters.

Some shark species can survive in freshwater as well as salt.