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

Implantation of acoustic transmitters in three specimens of Atlantic halibut (Hippoglossus hippoglossus) was performed, and the surgical procedure is described. Acceptable transmittance of heart rate signals was dependent upon attachment of both tag electrodes in the pericardial wall close to the heart muscle. Strong muscular action during burst swimming 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 months. A gradual decrease in pulse rate coinciding with a seasonal reduction in water temperature, day length and appetite was observed. A diurnal variation in heart rate was also detected. The fish showed little or no response in heart rate to certain farming procedures such as formalin treatment against parasites or cleaning of the tank. Bradycardia followed by increased heart rate after close interactions with larger fish was noticed in the first part of the recording period.