Aquafin CRC - Southern Bluefin Tuna Aquaculture Subprogram: net fouling management to enhance water quality and southern bluefin tuna (Thunnus maccoyii) performance
Aquaculture Management Consultants Pty Ltd
For tuna ranching to continue to develop it must improve the farming environment by providing optimum water quality to the tuna. This will improve the performance of farming operations and deliver quality products to the market and ultimately maintain Australian farmed tuna’s competitive edge. Also the next major step in the industry's sustainable expansion strategy is longer term holding (eg. 15 months). The above planned outcomes of the anti-foul project are important prerequisites to successful long-term grow out. The need for this project is quite obvious. If the culture environment is improved by the use of this product, more than likely the following will occur: • Increased water flow through the nets • Reduction in weight on farming structures • Reducing the re-suspension of sediments during rough weather • Reducing surface area for potential pathogens • Improving net handling techniques • Potential to increase longevity of nets • Reduce or eliminate the need for diving to clean equipment. • Improve cage integrity. This project aims to integrate and coordinate the industries approach on anti-foul treatments and ensure this meets with regulatory requirements. Furthermore, it is necessary to find out the efficacy of anti-foul treatments by monitoring key biological and farm husbandry parameters through trials on commercial farms. As mentioned previously, the research farm identified that the product tested showed promise and this combined with the industry panel work enabled the manufacturer to make the necessary alterations to formulations and make new products to improve performance in Spencer Gulf. Economically it is important to find out how long a single treatment will provide a reduction of fouling organisms given the current operating format of the industry. The cost to treat a net is significant but if the objectives are achieved then the benefits outlined in section B3 under “Need” will outweigh the costs. This includes whether nets need to be treated every season, or whether one treatment will reduce fouling over two seasons. There is a need to provide confidence that the active constituent found in the anti-foul treatments are not absorbed by the cultured organism (in this situation being tuna), is not found in the sediments and is not taken up by other marine organisms that are located nearby. Finally, it is a clear objective to disseminate results to industry every step of the way by forming close links with industry. Further to this extension role, results will be published in the “Tuna Brief” which is a recognised printed or electronic short communication within the tuna industry for disseminating research results. In addition, results will be presented at open forum industry research meetings.
1. Document current industry knowledge and methods used to control bio-fouling on nets and associated structures (both physical and chemical means) for various marine finfish species cultured in Australia and overseas.
2. Co-ordinate the tuna industries approach in antifoul treatments.
3. Review currently available commercial antifoulant products, including the mechanisms by which they reduce fouling and the regulations involved in their use.
4. Determine efficacy (through reduction in fouling growth and impact on net integrity) of antifoulant products identified by objective 3 with net panels in the local environment where tuna are currently ranched.
5. Identify the development pattern of fouling communities on commercial tuna cages that are subject to the current standard industry practices, and relate this to oxygen levels monitored on the outside and inside of these nets.
6. Establish relationship between the percentage cover of fouling communities with water flow, net weight and net drag.
7. Enhance the dissolved oxygen diffusion model to provide predictive capacity for industry to evaluate fouling management systems.
8. Field test the most effective anti-foul treatment identified by objective 4 on a commercial tuna cage with the typical industry regime of tuna stocking density, feeding and net maintenance. Effectiveness of the antifoulant will be assessed utilising methods developed and used in objectives 4 and 5.
9. Test the chemical residue status of tuna and shellfish within the cage and the sediment beneath the net for the treated cage and compare these to tuna, shellfish and sediment of an untreated control.
10. Assess the health status of tuna in the treated cage by comparing it with that of two control/untreated cages (health status incorporates behaviour, mortality and histopathology).
11. Disseminate results to industry on a regular basis through verbal, written and electronic communication.