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Fishing king crab off the Norwegian coast using relatively small collapsible pots Mussels may control SEA LICE in salmon R King crabs are packed for live export at Norway King Crab esearchers at the University of Maine have demonstrated that the blue mussel can eat the larvae of the sea louse, a parasitic pest which can decimate farmed fi nfi sh. The fi ndings, published in the journal Aquaculture, have implications for the farmed salmon industry in Maine. If further analysis in the fi eld holds up, using mussels on salmon farms could be another strategy to reduce the infectious pressure of sea lice on a fi nfi sh farm. Microbiologist Dr Sally Molloy was one of the team who made the discovery in mid-2010. The paper has implications for developing a concept called integrated multi-trophic aquaculture (IMTA), an alternative approach to the standard mono-culture aquaculture, in Maine. IMTA is believed to reduce the environmental impacts of commercial aquaculture systems by combining the cultivation of fed species, such as salmon, with extractive species, such as mussels. "Extractive species are fi lter-feeding, so they're taking in all the phytoplankton and zooplankton and whatever's in the water column. They're also taking in excess fi sh food and faeces and removing all those organics from the water," Molloy said. "The idea is hopefully that IMTA practices reduce the lobster is exported live, but this was not always the case. Table one shows the remarkable development of the lobster fi shery in New Zealand in the 20 years between 1988, when only 15 percent of the catch was landed live and the rest was sold frozen, and 2008, when 93 percent of the catch was exported live. This 20-year period saw a remarkable 78 percent increase in export of live lobster (from 15 to 93 percent of total catch), the commercial catches were reduced by 33 percent (from 4000 tonnes to 2680 tonnes). Yet during this period, the value of the fi shery more than doubled from $72.6 to $156 million, due to optimising landed product through live exports. This remarkable success story is due to many years of industry development, focusing on the specifi c needs of international markets, sustainable catch rates, an excellent stock monitoring programme and optimal techniques for holding and shipping rock lobsters. Norway is now exporting approximately fi ve percent of its king crab catch (TACC is approximately 1200 tonnes – see table two) but hopes to emulate New Zealand's success with spiny lobsters and export the entire catch. Without even realising it, New Zealand is a role model for invertebrate capture-based aquaculture in Norway, a country with one of the most developed aquaculture industries in the world. Finally, following the recent discovery of a number of deep-water king crab species in New Zealand waters (See: King-sized feasts lurk deep in New Zealand waters, www. stuff.co.nz, June 29, 2010) it is timely to consider the potential of the king crab fi shery in New Zealand and the possibilities for post-capture aquaculture of this species. nutrients going into the ecosystem because of the fi sh farm. It's sort of a greener version of farming. There are all kinds of other benefi ts because you're diversifying your product." The sea louse feeds on the skin and tissue of its host and has a life cycle consisting of 10 stages. Most research to eradicate sea lice infestations has focused on the stages of the louse when it has already infected its host. Farmers of fi nfi sh such as salmon and trout have used a drug called SLICE against the louse, but the parasite has shown resistance to the drug. The Maine research focuses on eradicating the sea louse in its larval stage. To conduct the experiment, the researchers collected sea lice egg strings from an infected commercial salmon farm in Maine. The eggs hatched and were reared to the copepodid stage. Meanwhile, the team obtained some local mussels and placed them in a system with artifi cial seawater. After the mussels were exposed to the sea lice copepods for either 30 or 60 minutes, the contents of the mussels' stomachs were removed and DNA analysis was performed. The analysis determined the mussels had ingested the copepodids. The team will take its work out of the laboratory and into the fi eld. They will lower a mussel raft into the waters of a salmon farm on the coast of Maine to fi nd out if their results hold up on a larger scale. The populations of mussels, salmon and sea lice will be monitored for several years to determine what effect they have on each other. "In our preliminary experiments we could see the mussels were capable of eating the sea lice, but we need to get a better understanding of disease dynamics on a farm," Molloy said. Should the raft prove effective, the IMTA technique could be combined with other methods, including chemotherapeutic drugs. SEPTEMBER/OCTOBER SEPTEMBER/OCTOBER 2011 R 2011 ■ NZ AQUACULTURE AQUACULTURE ■ 9