Salmon cage farming faces the widest range of fouling organisms of any aquaculture sector. Cages sit in open water for 18-24 month production cycles, and the nets provide an enormous surface area for colonisation.
The fouling community on a salmon cage net develops in waves. Hydroids arrive first — Ectopleura and Obelia colonies can cover a net panel within two weeks. Filamentous algae follow, trapping sediment and adding to the organic layer. Then come the heavy hitters: blue mussels in northern waters, Mediterranean mussels in the south, barnacles nearly everywhere. If left unchecked, a single cage net can accumulate 5-10 tonnes of fouling biomass over a summer season.
The impact on fish inside the pen is indirect but measurable. Fouled nets restrict water flow, cutting oxygen supply and trapping waste products. Bloecher, Olsen, and Guenther (Biofouling, 2013) measured 60% reductions in water exchange through heavily fouled nets. Fish in those pens ate less, grew slower, and showed higher size variation at harvest.
Most salmon farms manage fouling through mechanical cleaning — in-situ disc cleaners or ROVs that run along the net panel while fish remain inside. The typical schedule is every one to three weeks during the fouling season. Copper-alloy nets, silicone coatings, and cleaner fish provide complementary control.
The critical factor is timing. Cleaning at the hydroid and early mussel stage (before organisms cement hard) takes less time, causes less net damage, and releases less debris than waiting until heavy fouling has built up. Check the fouling season calendar for your region and use the cost calculator to budget fouling management expenses.