The bioenergetic implications for Murray cod (Maccullochella peelii) below a large hypolimnetic-releasing impoundment

River regulation has dramatically modified river landscapes, the distribution of physical habitats, and the physico-chemistry of rivers. In particular, hypolimnetic-releasing impoundments represent major discontinuities that disrupt downstream river environments (according to the serial discontinuity concept, SDC). When these hypolimnetic-releasing impoundments are operated to meet downstream irrigation demand, discharge (and hence flow velocity) and temperature regimes are usually impacted. These changes are often considered the most serious and continuing threats to the ecological integrity of rivers. In this thesis, I explored how changes in the flow velocity and temperature regime of an Australian lowland river (the River Murray) below a large hypolimnetic-releasing impoundment (Hume Dam) affect the bioenergetics of a threatened, large-bodied fish species (Murray cod, Maccullochella peellii). To explore these impacts, a bioenergetics model for juvenile Murray cod was developed. In constructing the model, a rapid non-lethal energy meter, capable of providing a more dynamic estimate of the energy density of Murray cod, was calibrated. Furthermore, Murray cod were identified as a low-energy species with high capacity for lipid and energy storage in this chapter.An understanding of how fish respond to flow velocity changes is an important consideration of their management in regulated flow velocity environments. As such, the first comprehensive assessment of the swimming capacity of the species was provided. Juvenile Murray cod were identified as swimming generalists, possessing a broad and moderate swimming capacity across body weight and temperatures. The species had low energetic demands (standard and active metabolic rate), and was a moderately efficient swimmer, with sufficient ability to repeat its prolonged performance.