In-Situ Net Cleaning Machine

In-situ net cleaning machines operate directly on deployed cage nets, removing fouling while fish remain inside the pen. Most systems use rotating disc heads or high-pressure water jets guided along the net surface by a diver or semi-automated frame. The operator works systematically from top to bottom, dislodging everything from slimy biofilm to heavily calcified acorn barnacles and hydroid colonies. Cleaning frequency varies — salmon farms in Norway typically run machines every 2-4 weeks during peak fouling season (May through September).

This approach has become the de facto standard across Scottish and Norwegian salmon production because it avoids chemical inputs entirely. Net mesh stays open, maintaining dissolved oxygen flow and reducing mechanical stress on moorings caused by drag on fouled panels. The tradeoff is cost: a single cleaning unit runs upwards of EUR 200,000, and each farm may need multiple units. Operational damage to nets is a real risk too — worn disc heads or excessive pressure can abrade nylon fibres, weakening panels and creating escape points. Most producers now budget net replacement into their cleaning cost calculations.

One often-overlooked issue is the fate of removed fouling material, which disperses into the water column during cleaning. In nutrient-sensitive areas, this organic loading can trigger localised oxygen depletion. Some farms mitigate this by collecting debris with suction systems or timing cleaning to coincide with strong tidal flow. For a full breakdown of how in-situ cleaning stacks up against coatings and other approaches, see the methods comparison page. The farm map also shows which CRAB project sites rely on this method as their primary fouling strategy.