Mytilus edulis has a smooth, elongated shell that ranges from dark blue to black, reaching 50–80 mm in length at maturity. The animal anchors itself using byssal threads — tough protein fibres secreted by a gland in the foot — which grip nylon netting, polyethylene rope, and steel equally well. Blue mussels are distributed throughout the North Atlantic, from the Norwegian coast south to the Bay of Biscay, and they thrive in the 4–18 °C range that characterises most northern European farm sites.
Dense mussel fouling is among the most expensive problems a salmon or trout farm can face. Aggregations regularly exceed 20 kg per square metre on untreated nets, enough to distort cage geometry and reduce enclosed volume by 10–15 %. The added weight strains mooring systems and can cause anchor drag during storms. Mussels also harbour sea lice larvae and other parasites between their shells, creating a reservoir of infection close to caged fish. Use the cost calculator to estimate how mussel fouling affects your site’s bottom line.
Settlement peaks between April and July in Scandinavian waters, with a secondary pulse in early autumn. Spat as small as 0.5 mm attach to biofilm-covered surfaces and grow roughly 1–2 mm per week in summer. Air-drying for 24–48 hours kills juveniles, but established adults survive extended exposure. Copper-alloy mesh prevents attachment entirely, though at 3–5 times the cost of nylon — compare methods here. The closely related Mediterranean mussel presents similar challenges in warmer waters. For seasonal timing details, check the fouling season calendar.
Control Methods
Manual removal Air-drying Copper-alloy mesh Freshwater immersion