Rippy-fish

Rippy-fish are creatures from the planet Lost Hope in Warhammer 40,000.

They are aquatic fish, rarely more 30cm in length and resembling the piranha of old Terra. Unlike their Terran variant, Rippy-fish could live in salt and fresh water and are immune to pollution, extremes of temperatures and poisons. Hundreds or even thousands of such a creatures roam the shallow waters of many planets posing a treat to every individual or vehicle that wants to cross water.

Don't confuse them with Ripperfish, which are more like killer Space Barracuda from Fenris instead of the Rippy-fish's Space Piranha schtick.