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FEATURE

IN-SITU CLEANING Clean nets, but what about the fish?

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A biofouling specialist gives us a concise overview of the problems involved

Malachi Stone from the International Aquafeed team talks to Björgólfur Hávarðsson MSc, about his presentation at Aquaculture UK

s some of our readers will know only too well, biofouling occurs when aquatic organisms colonise underwater structures such as nets used in aquaculture. Mussels, algae, hydroids and sea squirts will attach themselves to any available space, then grow and reproduce until the nets on your farm are

thoroughly clogged. Fouling of nets in and of itself is problem enough, but it also brings additional issues. These miniature forests of algae and ascidians provide a refuge and gathering place for hordes of salmon lice and other noxious parasites, such as amoebas and bacteria - a source of physical misery for the fish and economic misery for the farmer. At Aquaculture UK in Aviemore, Scotland, International Aquafeed had the opportunity to attend a talk on this very subject, given by Björgólfur Hávarðsson MSc from Steen-Hansen. His presentation, ‘In-situ cleaning: Clean nets, but what about the fish?’ gave listeners a great deal to think about. Steen-Hansen is a privately owned Norwegian company established in 1932. The company initially focused on paints before turning its attention to the chemical impregnation of nets for aquaculture. By 1995 it was in all major aquaculture markets, and today it is a world leader in antifouling paints for the fishfarming industry. The company now boasts its own production facilities, laboratories and R&D facilities. They had a turnover approaching US$20 million in 2014, and gross profits of more than US$350,000 the same year. They currently have 23 employees. Their aquaculture products include NetCoating PLUS™, protecting nets from abrasion and UV damage, and AquaNet® antifouling, which can be adapted to different environments and net materials.

Steen-Hansen’s own specialists have also published a useful, informative, Net Care Certified booklet in collaboration with their partners, agents and cooperating universities. The Little Book on Fouling™ is non-commercial and available free of charge (order at www.bookonfouling.com). You can even order different versions, depending on where you are in the world. This makes great sense: the flora and fauna clogging nets in Chile - and the conditions they do it in - will probably be somewhat different from those in Scotland. Even around the British Isles, Mr Hávarðsson says, the species involved, the intensity of accumulation and the length of the fouling season will all vary greatly, dictated by a combination of latitude and geography. It really does matter where you set up your farm. Most of the organisms that colonise the nets have planktonic larval stages. As such, they are carried on the sea’s currents until they come into contact with a surface they are ready to settle on. Easy to see, then, why the currents around a fish farm will determine much about the annual intensity of fouling and the intensity within the site. This will lead to marked differences in the levels of fouling between one site and another. Oceanic currents can thus be seen to greatly influence the establishment and size of the colonies of fouling organisms among which fish lice and other parasites love to hide. But they also influence the dispersal of the parasites themselves. Worse, in all this, the process may even be assisted by the farmer himself. In-situ high pressure cleaning of nets is a widespread biofouling management tool in Norway. One effect of such cleaning is net abrasion, which usually manifests as greater or lesser degrees of expansion in the net fibres, or even holes. Spaces between the fibres make for an even safer haven for all kinds of parasites to hide in, and for hydroid colonies to take root. Subsequent cleaning cycles will leave the hydroid roots intact, ready to immediately start growing again - and quicker than before, as the cleaning has now removed all competing species. The cleaning

26 | July | August 2016 - International Aquafeed

JUL | AUG 2016 - International Aquafeed magazine