Prawn farming effluent nitrogen is a potential polluter of coastal waterways. Consequently, environmental regulators are placing increasingly stringent discharge limitations on farmers, fuelling research into the development of cost-effective effluent treatment options. One such treatment option involves the cultivation of secondary, often detritivorous, crops (fish, prawns) in the presence of vertically deployed artificial substrates. Secondary crops could valuably assimilate effluent nutrients while the artificial substrate should improve bacterial effluent remediation processes, such as denitrification and nitrogen assimilation. Artificial substrates may also improve water quality and detritivore growth in systems containing detritivores. Furthermore, detritivorous secondary crops may improve substrate associated nutrient removal processes. The combination of substrates and secondary crops therefore, may enhance nutrient removal relative to their singular effects. The investigations outlined in this thesis have provided new knowledge regarding the cultivation of secondary crops in prawn farm effluent treatment systems containing artificial substrates. Detritivorous mullet assimilated effluent nutrients, and, artificial substrates improved both water quality and fish growth. At optimised C:N ratios, banana prawns were found to stimulate nitrogen assimilation and mullet enhanced substrate biofilm denitrification. Both grey mullet and banana prawns showed the potential to stimulate bacterial effluent remediation by increasing bacterial growth rates. The herbivorous S. Nebulosus, and to a lesser degree M. cephalus, showed they could be effective at harvesting, and assimilating, opportunistic macroalgae during effluent treatment.
Submitted in fulfillment of the requirements of the degree of Doctor of Philosophy, University of the Sunshine Coast, 2004.