Saltwater aquaculture
Marine Finfish
Marine finfish farming is a developing industry in NSW. Currently production and research focuses on a small number of species mulloway (Argyrosomus japonicus), yellowtail kingfish (Seriola lalandi) and southern bluefin tuna (Thunnus maccoyii). Mortalities have been reported, in both juvenile and adult marine finfish, which have been associated with organisms such as ciliated protozoan and monogenean trematodes. Heavily infested fish may lose appetite, flash or rub their bodies on tank surfaces, swim slowly, lose their flight response when attempts are made to catch them and show rapid or laboured gill movement. Heavy mortality can occur if diseases are left untreated, particularly at times of stress.
Nodavirus in Australian Bass
Nodaviruses have caused mortalities in a range of wild, farmed and ornamental marine fish worldwide. The first detected incidence of nodavirus in NSW occurred in Australian bass* at the Port Stephens Fisheries Institute (PSFI) Marine Fish Hatchery in 2004. This was the first time nodavirus had been detected in this species and the initial outbreak caused large losses of Australian bass fingerlings at PSFI.
The detection of nodavirus in Australian bass has had considerable implications for fish stockings in NSW. In order to allow continuation of stocking activities, whilst safeguarding the aquatic environment from the potential transmission of disease, a technical working group of national aquatic health experts was convened to assist policy development.
With support from the Recreational Fishing Trust and recreational fishing groups, NSW DPI is working with private and government hatcheries to develop a clearer understanding of the prevalence of the virus in Australian bass in NSW. All hatcheries producing Australian bass for stocking into public waters are required to undertake testing for presence of nodavirus prior to stocking permits being issued. Hatcheries are provided with the required equipment and training for preparation and submission of samples. The testing requirements for hatcheries have evolved since 2004 with considerable advances in testing availability and capacity. Since 2007, a real time polymerase chain reaction (PCR) has been used to test larvae for the presence of nodavirus.
In addition to this testing program, researchers are undertaking a comprehensive survey of wild Australian bass populations to assess the presence/prevalence of nodavirus in wild populations to better inform future management decisions.
Further research will enhance hatchery management of the disease and improve the understanding of impacts of nodavirus in the wild. Such information will continue to be adapted into risk based biosecurity policies.
*Australian bass is a euryhaline species, which means these fish are found in both freshwater and estuarine environments.