It is not known to evolve into or from any other Pokémon.
Qwilfish is a small, round fish Pokémon covered in many sharp spikes. These spikes are derived from its scales. It has a paddle-shaped tail which is about half of its body length, colored with a bluish line around the perimeter and two markings in the center of the pattern. The top of its body is a bluish color, while its underbelly is a pale cream color. Qwilfish has large pink lips.
The spines that cover its body are filled with a toxin which is known to cause fainting. It is able to fire these spines from its body by swallowing large amounts of water. This ability also makes this Pokémon appear bigger than it actually is, making it less vulnerable to predator attacks.
When faced with a larger opponent, Qwilfish swallows as much water as it can to match the opponent's size. Qwilfish also finds swimming somewhat challenging, due to its round form.
Qwilfish lives in a marine environment.
This Pokémon was unavailable prior to Generation I.