Strike a pose: Does communication by a facultative cleaner fish, the cunner wrasse (Tautogolabrus adspersus), facilitate interaction with Atlantic salmon (Salmo salar)?

Abstract

Tropical dedicated cleaner fishes communicate with client fishes to enable cooperative parasite removal, however, the ability of temperate facultative cleaner fishes to elicit cooperation through communication has yet to be fully investigated. Understanding the wider dynamics of communication in cleaning mutualism is particularly important for the salmon farming industry, because it uses temperate facultative cleaner fishes to control parasitic salmon-lice. To investigate whether cleaner-client communication might benefit parasite removal by facultative cleaners used in aquaculture, we observed interactions between cunner wrasse (n = 42) and their Atlantic salmon (n = 59) clients, which were either infected or non-infected by chalimus stage salmon-lice. We found that expression of two behavioural cues, cunners posing towards salmon and cunner making body-contact with salmon: (1) was higher when cunners were alongside infected salmon rather than non-infected salmon, (2) reduced the average distance between the cunner and trios of infected salmon, (3) increased the time cunner spent visually inspecting infected salmon, but, (4) did not decrease antagonistic interaction between the cunner and the salmon. Behavioural variation was high among individuals, nevertheless larger cunners (> 100 g) showed significantly higher rates of desirable mutualistic (e.g. inspection, pecking) and communicative (e.g. posing, contact) behaviours than smaller cunners. These findings imply this facultative cleaner wrasse displayed behavioural cues to infected clients which increased proximity and resulted in higher rates of mutualistic behaviours. If these two behavioural cues are subsequently shown to be correlated with delousing performance, then they could be used to identify high-performing elite cleaners for use in sea-farms and in selective breeding programs.