The heat resistance of normal, hypophysectomized and pituitary-autotransplanted goldfish acclimated to 20 °C under 16-h photoperiod and 8-h photoperiod conditions was determined. It was found that hypophysectomized goldfish were less heat resistant than normal fish and that those with an autotransplanted pituitary were as heat resistant as normal fish.The photoperiod results, though inconclusive, suggest that normal 16-h photoperiod fish are more heat resistant than normal 8-h photoperiod fish and that only the fish with a normal pituitary can respond to photoperiod changes. The fish without a pituitary are slightly less heat resistant than normal 8-h-photoperiod fish, while those possessing an autotransplanted pituitary are as resistant to a high temperature as normal 16-h-photo period fish.Treatment of hypophysectomized goldfish with luteinizing, thyrotropic, adrenocorticotropic, and lactotropic (prolactin) hormones and crude salmon pituitary extract appeared not to affect resistance to a high temperature.In the experiments involving pituitary autotransplantation, a study was made of various organs influenced by pituitary secretions to determine the pattern of hormone output by the pituitary. By contrasting this information with that of the heat resistance tests, various hormones have been suggested as not playing an essential role in high temperature resistance. The hypothesis is put forward that a prolactin-like hormone plays the essential role in resisting a high-temperature stress.
The source ofYersiniaspp. in pasteurized milk: an investigation at a dairy
