Knifefish that can emit powerful electrical bursts in water

Electric Eels are not true eels in the strictest sense, but rather members of the knifefish family, though this is purely technical distinction. Adults are about 6 feet in length and weigh about 450 pounds each. They are found in fresh water in warm climates.

Non-aggressive fresh water dwellers, preferring warm water

Electric eels are non-aggressive fresh water dwellers, preferring warm water. If an electric eel feels threatened or is attacked it will discharge a jolt of electricity. This electrical charge causes any creature within 5-ft of the eel to take 3d8 points of damage, all creatures within a 5-ft to 10-ft range will take 2d8 points of damage, and all creatures within 10-ft to 15-ft take 1d8 hp damage. No saving throw is allowed, though certain magic items and spells may grant immunity or reduced damage from the electrical attack. Rumours persist of a saltwater electric eel which is double the size and delivers a jolt twice as powerful. Treasure: None