Life in the fast lane: The free-ranging activity, heart rate and metabolism of an Antarctic fish tracked in temperate waters

Abstract

The fish species Notothenia angustata inhabits temperate waters (10 °C), yet retains physiological traits that show it once existed at sub-zero temperatures. We determined the free-ranging activity, heart rate and metabolism of N. angustata and compared it with Notothenia coriiceps, an ecologically and morphologically congeneric cousin that still inhabits sub-zero waters. Firstly, the association between heart rate ( fH) and oxygen consumption ( MO 2) was first determined in the laboratory. The fish were then released into their respective environments and fH recorded by a miniature archival electronic tag, from which the metabolic rate of the free-ranging fish was extrapolated. Free-ranging activity of wild fish was monitored throughout the study using implanted acoustic tags and a static hydrophone array. Results showed that the difference in standard metabolic rate (SMR) between N. angustata and N. coriiceps fitted the Arrhenius model for inter-species thermal sensitivity in fish ( Q 10 = 1.76). However, the inter-species disparity in total metabolic rate (TMR) was far greater. This was attributable to N. angustata swimming at higher speeds and covering a 5-fold greater area over 24 h compared with N. coriiceps. As a result, activity (and associated feeding) comprised a far larger portion of TMR in N. angustata (27.9%) than for N. coriiceps (5.7%). We conclude that the increased time spent swimming by N. angustata was presumably to forage for food to acquire sufficient energy to fuel its elevated SMR. This resulted in a much greater inter-species difference in TMR than may be predicted by the disparity in environmental temperature.