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the area of weed infestation. They and their enclosure can be removed once the target invasive weed has been eradicated. MPI Senior Science Adviser Andrew Bell says the recent successful trial was carried out at Waikato's Lake Karapiro treating the widespread pest weed hornwort. "This novel approach was so effective that MPI now has it in the toolbox for use should the "unwanted organism" hornwort be found in South Island lakes. Local iwi supported the project and are interested in the results and the potential to use grass carp as a biological control tool. They recognise that grass carp may have a role not only in biosecurity responses when hornwort occurs in new locations, but also as a potential invasive weed management tool in hydro dams and other sites in their areas." Grass carp have been used successfully for the control of large infestations of other invasive weeds in New Zealand lakes since they were introduced in the late 1960s from Malaysia. They are a natural aquatic weed controller and are unable to breed in the wild in New Zealand, unlike koi carp which breed well and have become a pest species. The team built six large enclosures 2.5m deep and 6m wide, and placed them within hornwort beds in Lake Karapiro. NIWA principal scientist aquatic plants, Dr John Clayton says, "The cages contained different numbers of fi sh in order to establish the most effective stocking rate required for rapid removal of nuisance weed within the enclosed area. Three to fi ve fi sh per enclosure were found to be effective and very fast, with weed in the enclosed areas removed in nine weeks." Designing enclosures that were escape- proof was particularly challenging for the NIWA team, but Dr Clayton says the end result was an innovative design that has animal ethics committee approval. NEW DIETS TO COUNTER GLOBAL WARMING Research by Skretting in Norway and Tasmania anticipates the problems that climate change will bring with warmer waters to the coast especially in summer. Work began in 2010, investigating the effects of high temperature on gut integrity. Previous investigations had demonstrated that the gut wall is more permeable at higher temperatures, making the fi sh more vulnerable to invasion by pathogens, faster metabolism of anti-oxidants and that disruption of the gut wall leads to loss of appetite. Diet modifi cations to counteract the loss of anti-oxidants by adding an appropriate anti-oxidant to the feed to help stabilse the gut, was tested in high temperature trials and scientists fount that fi sh were healthier, RESEARCH, CONSULTING AND LABORATORY ANALYSIS Aquaculture research Aquaculture impact assessments and consents Biosecurity and pest management plans Mobile: 021 259 0646 Home: 09 533 4431 Recognised and recommended by Professional Skipper magazine as one of our leading marine artists. Email: pauljilly@vodafone.co.nz Website: www.marineartgallery.net.nz SEPTEMBER/OCTOBER 2012 ■ NZ AQUACULTURE ■ 5 IANZ accredited seafood laboratory Fisheries assessments and management systems Adaptive management plans CAWTHRON INSTITUTE Ph +64 3 548 2319 info@cawthron.org.nz www.cawthron.org.nz ate more, grew better and had a lower feed conversion ratio. Skretting translated the results into commercial grower feeds for salmon in Norway and Tasmania. They found that the high protein formulations conventionally used over summer in the Australian salmon industry led to higher excretion of nitrogen. Diet modifi cations to counteract the loss of anti-oxidants by adding an appropriate anti-oxidant to the feed, with lower protein levels, was tested in high temperature trials and scientists found that fi sh were healthier, ate more, grew better and had a lower feed conversion ratio and lower nitrogen outputs. NAMIBIAN FISH FARMERS' PLEA FOR EQUIPMENT Aquaculture farmers at the Karovho Fish Farm in the Kavango Region have put out a call for equipment and transport vehicles for their underperforming fi sh farm. Employees at the farm say they are in dire need of a range of equipment to help them operate and monitor water quality in the fi shponds. They are also calling for insecticides and pesticides, and would like to upgrade the quality of the feed used. Several fi sh breeds such as Tilapia, and Three Spot and sometimes Catfi sh are bred at the farm. VIP.S86 VIPP.AC4 45