The relationship between caudal differential pressure and activity of Atlantic cod: a potential method to predict oxygen consumption of free-swimming fish

This study reports the first results on telemetry of caudal differential pressure during spontaneous swimming activity in cod Gadus morhua and demonstrates that tail‐beat pressure may be used as a predictor of activity and swimming costs of free‐swimming cod. Tail‐beat pressure was monitored using a differential pressure sensor on the caudal peduncle of cod and spontaneous swimming activity was quantified using a customized video‐computer tracking programme. Tail‐beat pressure was found to correlate with (1) swimming speed (U) and oxygen consumption during forced swimming and (2) mean U during spontaneous activity. Based on the relationship between and the integrated pressure performed by the tail during forced swimming, it should be possible to predict during spontaneous activity. To gain precise measures of activity and thus predictions of for free‐swimming fish, however, individual calibrations are necessary.