The effect of hypophysectomy on freshwater survial in teleosts of the order atheriniformes

Ten species of teleosts belonging to three families of Atheriniformes (Poeciliidae, Cyprinodontidae, Goodeidae) have been tested for their ability to survive in fresh water without a pituitary gland. The fish of the current report respond similarly to Atheriniformes previously investigated. Hypophysectomized fish enter into osmotic shock and generally die within three weeks when placed into fresh water but they will survive in dilute sea water (1.2% solution of commercial sea salts). Fish belonging to Poecilia survive for the shortest period. By comparison the mean survival time for Xiphophorus is longer and more variable. No correlation exists between the number of days hypophysectomized fish are held in one third sea water prior to testing and the length of time they survive in fresh water. This is also true for fish challenged a second time after recovering from osmotic shock. Presumably, osmotic difficulty commences upon exposure to fresh water but can be alleviated when fish are returned to dilute sea water. Five hypophysectomized fish survived in fresh water. Each of these exceptional animals had suffered brain damage during surgery. The significance of these observations is discussed as it is related to the natural habitat and salt tolerances of the fish studied.