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Keywords:

  • Swimming capacity;
  • body mass;
  • temperature;
  • ambush predator;
  • Maccullochella peelii

Abstract

This study documented the swimming capacity of a large ambush predator, Murray cod Maccullochella peelii, endemic to the Murray-Darling Basin, Australia. It was evident that the species is a swimming generalist, maintaining moderate ability across all aspects of the swimming capacity parameters that were investigated. For instance, the species was capable of prolonged swimming performance (critical swimming speed, Ucrit: absolute, 0.26–0.60 m·s−1, relative, 1.15–2.20 BL s−1) that was inferior to active fish species, but comparable with other ambush predators. The species had low energetic demands, maintaining a low mass-specific standard (21.3–140.3 mg·h−1 kg−1) and maximum active metabolic rate (75.5–563.8 mg·h−1 kg−1), which lead to a small scope for activity (maximum active metabolic rate–standard metabolic rate; 1.4–5.9). They were reasonably efficient swimmers (absolute and relative optimal swimming speed, 0.17–0.61 m·s−1 and 0.77–1.93 BL·s−1, respectively) and capable of repeat bouts of prolonged performance (recovery ratio = 0.99). Allometric changes in aspects of swimming capacity were realised with body mass, whereas broad swimming capacity was maintained across a wide range of temperatures. The swimming capacity demonstrated by Mpeelii reflects a sit-and-wait foraging strategy that seeks to conserve energy characteristic of ambush predators, but with distinct features (e.g., lack of fast-start ability) that may reflect their evolution in some of the world's most hydrologically and thermally variable rivers.