A method for hypophysectomy of the sexually mature sterlet, Acipenser ruthenus L., and the state of the fish after the operation.

Hypophysectomy was performed on sexually mature sterlets, Acipenser ruthenus L., in summer and autumn. The operation usually lasted about 45 sec, but never longer than 90 sec. After the parasphenoid was stripped, an ellipsoid hole was trepanated at the level of the eyes. The hypophysis was ablated by catching its rostral end with a pincer. As the result of the extirpation of the hypophysis the majority of the specimens grew steadily lighter, and a considerable loss of the body weight as well as macroscopical changes in the internal organs were observed. The survival rate after the operation was 100% among the fish operated on in autumn and 74-81% of those operated on in summer. Histological examination verified completeness of the extirpation of the gland. The saccus vasculosus was ablated partially or fully together with the hypophysis and the bottom of the infundibulum of the diencephalon was injured in 20-25% of the animals. However, the preoptic nucleus and the proximal part of the preoptic-hypophysial tract were not damaged.