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Carp carcass decomposition and water quality: implications for the release of CyHV3 as a biocontrol agent for common carp in Australia

Richard Walsh, Tyler Dornan , Sanjina Upadhyay, Hamish Brookes, Matthew Hipsey, Mark Laws, Phillip Cassey, Justin Brookes

Abstract

Context: The common carp, an invasive pest in Australia's Murray-Darling Basin, is targeted for population control via the potential biocontrol agent, cyprinid herpesvirus (CyHV-3). The long-term ecological benefits are clear, but immediate environmental impacts from mass fish mortality are less understood. Aim: This research aimed to understand the effect of a mass fish mortality event on water quality. Methods: Experiments of increasing scale (bucket, mesocosm, and wetland experiments) were conducted to assess how decomposing carp carcasses alter DO and nutrient concentrations in water. Key results: Dead carp added to mesocosms decayed more rapidly at 18°C than 12°C, yielding oxygen demands of 1.022±0.029 mg/kg/min and 0.496±0.239 mg/kg/min, respectively. As these carp decayed, they released phosphorus yielding 2,106.7±180.98 mg/kg. In the wetland experiment, carp addition of 2,400 kg/ha resulted in anoxic conditions over the following two weeks. The release of dissolved organic carbon and lipids led to a peak biological oxygen demand of 95.3 mg/L. Conclusions: Carp decomposition considerably contributes to BOD and algal growth through nutrient enrichment and is strongly influenced by carp density. Implications: The finding highlights key factors to consider before using biocontrol agents causing mass carp mortality, including hypoxia, anoxia and increased risk of harmful algal blooms.

MF24183  Accepted 12 December 2024

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