Rensefisk

Rensefisk is a Danish term that refers to fish that engage in cleaning symbiosis, removing ectoparasites, dead tissue, and detritus from other fish. This behavior occurs in many tropical, subtropical, and temperate marine ecosystems, and is most commonly observed among cleaner wrasses and cleaner gobies. In natural habitats, client fish visit cleaning stations where they allow cleaners to pick parasites and neglected tissue; in return, cleaners receive a meal.

The cleaning interaction is highly specialized. Cleaners and clients often communicate through color patterns, specific movements, and tactile signals that indicate willingness to clean and readiness to be serviced. These relationships are typically mutualistic: clients benefit from reduced parasite loads and improved condition, while cleaners gain nutrition and sometimes protection within their home station.

In aquaculture and fisheries, rensefisk refers to certain species kept to control external parasites on farmed fish, such as salmon and trout. Common examples in European contexts include the ballan wrasse (Labrus bergylta) and the goldsinny wrasse (Ctenolabrus rupestris). The use of rensefisk can reduce the need for chemical treatments, but it requires careful management to ensure the fish survive, effectively reduce parasites, and do not introduce new disease risks to farmed stocks.

Ecology and management considerations include the impact of stress, pollution, and habitat degradation on cleaning interactions, as well as the welfare and compatibility of rensefisk in both wild and farmed environments. In aquarium settings, providing appropriate cleaning stations and compatible tank mates supports healthy rensefisk populations.