There is an urgent need to develop and commercialise treatments for the control of amoebic gill disease in the Atlantic salmon aquaculture industry in Tasmania. The cost-benefit analysis undertaken by the Aquafin CRC suggested a net present value of economic benefit of $21.6M AUD and a benefit/cost ratio of 5.3. The need for short term (even interim) solutions for the control of AGD is paramount.
This project complements and continues the advances made by previous research (FRDC 2000/266 and 2001/205) that identified potential treatments. The current project will investigate commercial feasibility of treatments previously identified while providing an opportunity for examining new potential AGD treatments at the behest of the salmon aquaculture industry. Industry representatives, in a recent meeting, (January 15, 2004 Marine Research Laboratories, Taroona TAS) iterated the need for a flexible program that would allow potential treatments and control measures to be tested in the laboratory as well as in the field. This proposal (with budgetary constraints) has been developed to provide that flexibility with clearly identified treatments that will be investigated in the first instance. The road to commercialisation of any disease control treatment is a long and complex one, this project is designed to provide the information that may lead to a change of commercial practice in the control of AGD.
A program for the development and commercialisation of disease treatments is grounded in the identification of potential treatments that are tested both in vitro and in vivo in the laboratory. Once suitable laboratory testing is complete, then small-scale field trials are required and finally the scaling up of trials for commercialisation. A program for treatment develop must operate over a minimum of a 3 year funding cycle to maximise the likelihood of success maximising the productivity and contributions of all staff (Research leaders, technicians, post-doctoral fellows and graduate students). Through this approach, the outcomes of the research can be achieved, providing tangible solutions for industry, the acquisition of knowledge and intellectual property for the CRC and the training of quality personnel (Post-docs and PhD students).
Prior to this project there had been investigations into some potential candidate amoebicides, with little success except for the possibility of oxidative disinfectants such as chloramine-T. This project has since tested a number of amoebicides using a progressive approach of in vitro toxicity, in vivo efficacy in the laboratory through to in vivo efficacy under field conditions in either semi-commercial or under full commercialised field trials.
Although the practical delivery of some of these as treatments of amoebic gill disease (AGD), such as chloramine-T bathing, appear not to be practicable, other avenues may have potential for further commercial development, such as the dietary inclusion of potential amoebicidal compounds, including bithionol and ionophore-based amoebicides. The project has explored the potential of bithionol, a registered amoebicidal drug, as an in-feed treatment, showing that AGD severity can be reduced by approximately 50%. Similarly, the project has examined the efficacy of an immunostimulant-based feed additive, Aquacite and Betabec which reduced mortality in Atlantic salmon with AGD but did not affect the intensity of infection.
This project has further characterised the effects of gill disease, in particular AGD, with respect to the metabolic cost of disease to the fish. This work has estimated that in excess of 17% of the ingested energy is likely to go to service the cost of AGD. This approach provides a useful tool to incorporate into bioeconomic models for assessing the efficacy of AGD treatments in the future.
Keywords: Amoebic gill disease, Atlantic salmon, disease treatment.