Darwin in the Northern Territory, Australia, was once home to a small number of prawn farms established in the 1990’s. Nowadays, all these farms are either laying empty or have been repurposed for farming of other aquatic species. There were likely a number of contributing factors though anecdotally a common issue was the enormous abundance of wild prawns (Metapenaeus spp.) and predation by birds. On the east coast of Australia, there is a well-established and highly successful tiger prawn (Penaeus monodon) farming industry. These farms operate using semi-intensive farming methods with stocking densities in the range or 30-50 post-larvae (PL)/m2. As an alternative approach to farming tiger prawns in northern Australia, we are exploring extensive, low input farming that could be more location appropriate for the region and remote communities. This offers the potential to unlock large areas of the coastal regions of northern Australia to be used for aquaculture.
To investigate the potential challenges of farming tiger prawns in the north, we collaborated with a local farm south of Darwin. Here we carried out pond-based experiments using a stocking density of 3 PL/m2, supplemental feeding at a 50% ration, chemical treatment to exclude wild prawns and have excluded birds from one pond using netting. We also performed a controlled tank-based experiment to compare different water treatment methods and their effect on wild prawn exclusion and productivity of tiger prawns. Water treatment methods included chemical treatment prior to stocking, filtration of water through 50 um mesh screen and non-treated raw water. Results showed the presence of wild prawns significantly impacts productivity of the tiger prawns through restricting growth, reducing survival and increasing FCR (Table 1). Interestingly, the presence of wild prawns did not impact total biomass and FCR in the tanks.
Findings from these first trials have confirmed some of the challenges of farming tiger prawns in northern Australia, and solutions to common competitors and predators have been developed that will likely play a role in future extensive farming models.