The red neon, Paracheirodon axelrodi (Schultz, 1956), is able to survive in distilled water

In the current paper we report on the ecophysiological adaptation of the red neon toextremely low water hardness (nearly zero). Such adaptations of aquatic vertebrate species (either fishor frogs) to extreme environmental conditions show a large plasticity of this group even if, by definition,the aquatic environment is quite stable and homogeneous.