Once Humans The Way of Winter update not only adds new regions and temperature mechanics but introduces a whole new collection of Deviants. These Pokemon-like creatures can be found hidden across the overworld and have unique abilities and benefits. Out of all the new Deviants, Hydronaut Fish stands out as a rare catch. Hydronaut Fish is a Territory Deviant in Once Human, which means it can give you a hand with certain tasks around your base. Read on to learn where to find the Hydronaut Fish Deviant.