Recording long‐term heart rate in Paranotothenia angustata using an electronic datalogger

A unique heart beat datalogging device was either surgically implanted into the peritoneal cavity (internal‐fish) or attached by nylon anchor tags to the dorsal fin rays (external‐fish) of the black cod Paranotothenia angustata . Both groups had a mean ± s . e . heart rate of c . 46 beats min −1 after 24 h, and by 20 days external‐fish showed a significant reduction (34 ± 3 beats min −1 ) whereas internal‐fish did not (44 ± 2 beats min −1 ). In demersal fishes external attachment of an electronic recording device may be preferable to surgical implantation.