The swimming capacity of juvenile Murray cod (Maccullochella peelii): an ambush predator endemic to the Murray-Darling Basin, Australia

MDFRC item.

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, U crit : 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 M. peelii 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.