Morphological Adaptations of Cyprinodontoids for Inhabiting Oxygen Deficient Waters

Abstract

A previously unrecognized morphological adaptation of fishes to oxygen depletion is described. Natural oxygen depletion was simulated by use of sodium sulfite. It was demonstrated that some fishes are adapted to permit use of an oxygen rich layer of water at the atmosphere-water interface. Representative cypronodontoids (Fundulus notatus, Gambusia affinis, and Poecilia reticulata) exhibited maximum adaptation and the greatest survival ability of the species tested. Notemigonus crysoleucas, Brachydanio rerio, Lepomis macrochirus, and L. cyanellus, representing other suborders, showed less adaptation to these conditions and correspondingly lower survival. Micropterus salmoides seemed unadapted for survival in oxygen depleted waters. Carassius auratus exhibited a physiological adaptation, but used the oxygen rich surface water as a supple-