Both wrasse and lumpfish eat fouling organisms off salmon cage nets, but they are very different animals with different strengths. Farms choosing biological control need to match the species to their site conditions.
Ballan wrasse (Labrus bergylta) are the original cleaner fish in European salmon farming. They are territorial, long-lived (up to 20 years), and graze actively on hydroids, small mussels, and crustaceans. Goldsinny wrasse (Ctenolabrus rupestris) are smaller and focus more on sea lice than fouling, but contribute to both. Wrasse work best in warmer waters — they feed actively above 8-10°C and become sluggish below that. In Norwegian and Scottish farms, wrasse feeding drops off sharply from October through March.
Lumpfish (Cyclopterus lumpus) are cold-water specialists. They tolerate temperatures down to 4°C and keep feeding through winter when wrasse shut down. Lumpfish are also easier and cheaper to breed in captivity — hatchery production has scaled rapidly since 2015. The downside: lumpfish are short-lived (typically deployed for one production cycle) and grow fast, eventually becoming too large for effective cleaning behaviour.
Feeding behaviour differs. Wrasse pick individual organisms off the net surface — a slow, thorough grazing pattern that works well on sparse fouling. Lumpfish tend to rasp and suction, better suited to biofilm and soft fouling but less effective on hard-shelled barnacles. Neither species can remove cemented adult barnacles or calcareous tubeworms.
Stocking density matters. The industry standard is 4-5% of salmon numbers for wrasse, slightly higher for lumpfish. Too few cleaner fish and the fouling effect is negligible. Too many and competition for supplementary feed creates welfare problems.
Mortality is a concern for both species but worse for wrasse. Wild-caught wrasse suffer high transport and acclimation mortality (30-50% losses are not unusual). Captive-bred lumpfish adapt better to cage conditions but are susceptible to bacterial infections. Both species need shelter structures — kelp hides, pipes, or purpose-built hides — inside the cage to reduce stress and provide feeding territory.
The trend in the industry: farms in colder waters (northern Norway, Shetland, Iceland) favour lumpfish for their winter activity. Farms in warmer southern Norwegian and Scottish waters use wrasse, sometimes mixing both species. Neither replaces mechanical cleaning — they supplement it. Compare all approaches in the anti-fouling methods comparison.