Ecology and bioenergetics of the gudgeon (Hypseleotris spp.) in Maroon Dam: a zooplanktivorous fish in a whole-lake biomanipulation

Abstract

Gudgeon (Hypseleotris spp.) are the most widespread and abundant native Australian freshwater fish and the dominant zooplanktivore in Maroon Dam, the site of Australia's first whole-lake biomanipulation experiment. The spatial (littoral and pelagic) and temporal (diurnal and seasonal) distribution and diet of Hypseleotris was examined following the addition of 100,000 piscivorous Australian Bass (Macquaria novemaculeata) to Maroon Dam in the summer of 1998/99. A strong spatial and temporal ontogeny was observed, with smaller (<16 mm SL) Hypseleotris dominating the pelagic, an intermediate (12-20 mm SL) size class diurnally migrating between littoral and pelagic, and larger fish (>20 mm SL) remaining in the littoral throughout the day and night. Spatial ontogeny affected diet also, with fish consuming a decreasing proportion of zooplankton and an increasing proportion of macro-invertebrates as fish length increased and habitat use changed. A bioenergetics model was constructed to examine these distribution and diet patterns. Laboratory derived consumption and respiration parameters were combined with caloric densities and commonly accepted excretion and activity scalars to produce modeled growth estimates that were validated against Hypseleotris age-at-growth data collected from a diversity of habitats. Using this model, it was concluded that the spatial and temporal ontogeny and diet of Hypseleotris in Maroon Dam described the most energetically advantageous life history. Unlike many zooplanktivores in northern hemisphere lakes, Hypseleotris did not appear to engage in migratory predator avoidance behaviour. This is discussed in a context of Australia's paucity of pelagic piscivores. It is concluded that top-down biomanipulation by stocking of native piscivores has only a limited application in Australia, and that other biomanipulation techniques may prove more successful.