APPLICATION OF HEART-RATE TRANSMITTERS IN BEHAVIOR STUDIES ON ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS)

Implantation of acoustic transmitters in three specimens of Atlantic h alibut (Hippoglossus hippoglossus) was performed, and the surgical pro cedure is described. Acceptable transmittance of heart rate signals wa s dependent upon attachment of both tag electrodes in the pericardial wall close to the heart muscle. Strong muscular action during burst sw imming and the capture and swallowing of food severely interfered with transmitted heart signals. The heart rate of one male halibut kept in a large tank with 50 other halibuts was recorded continuously for 4 m onths. A gradual decrease in pulse rate coinciding with a seasonal red uction in water temperature, day length and appetite was observed. A d iurnal variation in heart rate was also detected. The fish showed litt le or no response in heart rate to certain farming procedures such as formalin treatment against parasites or cleaning of the tank. Bradycar dia followed by increased heart rate after close interactions with lar ger fish was noticed in the first part of the recording period.