The main purpose of this symposium to present and discuss data about the combination of morphological, physiological and biochemical traits and fish phylogenies obtained with the ‘one gene-one phylogeny’ method.    Each speaker will be challenged to combine information on morphology, genetics, and physiology with that widely used in the modern molecular systematic studies. Emphasis will be given to the physiological and biochemical characteristics related to environmental adaptation such as oxygen, temperature, draught, pressure, and so on.