This proposal is fulfilling objectives of Aquafin CRC Centre Agreement and it is within the key research areas for Aquatic Animal Health Subprogram Strategic R&D Plan.
Aquafin CRC Centre Agreement:
This proposal fulfils the objective to reduce economic impact of disease in finifish farming (Program 3 Health) and provide environmentally friendly approaches to disease management (Program 3 Health). It falls within Subprogram 3B Management and control of Amoebic Gill Disease of Atlantic salmon.
Aquatic Animal Health Subprogram Strategic R&D Plan:
- aquatic animal health management
This proposal will establish AGD management on the farm
- best practice
Results of this project will contribute to the development of Regional Codes of Best Practice for Health, which is one of the priorities in the R&D Plan
- nature of disease and host-pathogen interaction (improved knowledge of the host-response to disease agent)
Parasitic protozoans are one of the priority groups for this key research area. This proposal also will contribute to evaluation of host-pathogen ineractions for intractable diseaess and identify risk factors to develop disease minimisation risk.
- training and capacity building (human capital development)
This proposal will provide training for one postdoctoral fellow and contribute to consolidation of knowledge and capability for parasitology of aquatic animals, which is one of the priorities
Need for research
There is a clear need to broaden the almost exclusive approach of managing AGD by treatment only. Identification of husbandry practices that lower disease incidence will be of immense value in curtailing the currently excessive costs of treatment. Understanding the reasons for reduced disease incidence within different salmon sub- populations at the farm level will have numerous flow of benefits to other AGD related research. In the recent AGD research survey of Tasmanian salmon producers it was stated that:
”Section role of farm management still needs some work particularly in the area of mature fish and lights. Farm observations show mature and lit fish being susceptible to infection and triploid fish having an apparent resistance to infection. We feel that study of the mechanisms involved in these examples should lead to a better understanding of the host-pathogen interaction”.
Disease outbreaks are a function of the interaction between host, pathogen and their environment. Under culture conditions it is impossible to prevent interaction between a pathogen and its host; however, the proposed study presents an opportunity to gain further knowledge, which can directly influence current industry approaches, regarding the effects of manipulating the host and its environment.
Investigation of infection in relation to these different production strategies; ie, artificial lighting, triploids and maturation will improve management of AGD and lead to reducing AGD impact on the industry. This project will provide industry with a more detailed appraisal of AGD in the field, over a longer time period, incorporating multiple treatments and seasonal changes. The advent of enhanced understanding of AGD provided by this project will provide salmon industry with alternative, environmentally friendly strategies to lower production costs of which AGD mitigation is a significant part.
Before this project our knowledge of the effects of husbandry on Amoebic Gill Disease (AGD) was limited. This project allowed on-farm assessment of effects of husbandry procedures and stock characteristics on AGD severity. Furthermore, we investigated the potential to re-use fresh water for more than one bath. Preliminary results were promising. Further trials, including some on a larger scale should be undertaken to confirm that re-use of freshwater bath has a commercial potential.
Out of season smolt subjected to artificial lighting regimes and transferred to estuarine sites, where a marked halocline is present, required earlier bathing than fish from cages where no artificial lighting was used. However the advantage of fish subjected to artificial lighting not maturing would outweigh the disadvantage of the need for an earlier bath. This is because maturing fish were more affected by AGD than non-maturing fish. Neither supplemental oxygenation nor high-energy diet affected AGD. There was no statistically significant difference between males and females with regard to AGD. There was no evidence that ploidy had an effect on AGD, however the trial was compromised by the priorities of commercial farm management. There was no significant effect of gill damage on the severity of Amoebic Gill Disease.
In conclusion, this project has not only increased our understanding of the effects of husbandry on AGD but also has enhanced our ability to investigate AGD in the future. This will ultimately lead to direct benefits for the salmon industry.
Keywords: Amoebic Gill Disease, salmon, aquaculture, freshwater bathing