title: Delousing efficiency of farmed ballan wrasse (Labrus bergylta) against Lepeophtheirus salmonis infecting Atlantic salmon (Salmo salar) post-smolts.
abstract: BACKGROUND
  Cleaner-fish (wrasse, Labridae) are increasingly deployed within the Atlantic salmon (Salmo salar L.) industry as a biological control against sea-lice (Lepeophtheirus salmonis Krøyer). Two tank-based trials were performed to test the effect of farmed ballan wrasse (Labrus bergylta Ascanius) body mass and supplementary feeding on the delousing of Atlantic salmon post-smolts with an initial infection level of ∼12 lice salmon(-1) and a ∼5% wrasse:salmon ratio.
  
  
  RESULTS
  Sea-louse levels below 0.5 lice salmon(-1) were obtained within 84 h, and preferential preying upon larger motile stages was found. The wrasse body mass and the availability of fresh, opened blue mussels (Mytilus edulis L.) did not significantly affect delousing efficiency. The functional predator response was linear, showing no minimum prey density threshold for sea-louse foraging and no satiation plateau, in spite of the high consumption rates measured. Sea-louse infection levels declined following a one-phase exponential decay model, with a standardised decline time constant of 0.8-1.3% h(-1) for each wrasse stocked per 100 salmon.
  
  
  CONCLUSIONS
  Farmed ballan wrasse are confirmed as highly effective therapeutic and preventive biological controls against sea-lice. The study supports the current minimum hatchery size target (10 mm total length) and the use of supplementary feeding to sustain the wrasse stocks in operation. The functional predator response and the standardised decline time constant of sea-louse abundance are proposed as useful indicators of delousing efficiency.
authors.affiliation: Institute of Aquaculture, University of Stirling, Stirling, Scotland, UK.
authors.forename: Eric
authors.initials: E
authors.lastname: Leclercq
authors.forename: Andrew
authors.initials: A
authors.lastname: Davie
authors.forename: Hervé
authors.initials: H
authors.lastname: Migaud
mesh_terms: D000818:Animals; D017756:Aquaculture / Q000379:methods*; D033342:Copepoda / Q000502:physiology*; D004478:Ectoparasitic Infestations / Q000517:prevention & control*; D005247:Feeding Behavior / Q000502:physiology; D005393:Fish Diseases / Q000469:parasitology* / Q000517:prevention & control*; D010473:Perciformes / Q000502:physiology*; D010572:Pest Control, Biological / Q000379:methods*; D011235:Predatory Behavior; D020317:Salmo salar / Q000469:parasitology*
keywords: Atlantic salmon; biological control; delousing; farmed ballan wrasse; functional predator response; sea-lice