Frontiers in Marine Science (Nov 2015)
The ecological significance of juvenile Diplodus sargus as ectoparasite fish cleaners in the north-eastern Atlantic
Abstract
Cleaning behaviour was recently described for the omnivorous species Diplodus sargus. Although previous studies have reported the existence of ectoparasites in the stomach contents of some individuals this commercially important fish was never considered a cleaner species. Here we make the first characterization of this behaviour based on field observations. This behaviour was exclusively performed by juvenile D. sargus and, until now, was only observed in confined or semi-confined areas such as coastal lagoons or harbours. Unexpectedly, cleaning rates and the number of individuals performing this behaviour largely exceeds the ones described for a sympatric cleaner fish (13.98 cleaning events/individual/hour compared to 5.08 in Centrolabrus exoletus). Clients belong to several fish families (e.g. Mugilidae, Sparidae and Labridae) that include some of the most common species in coastal habitats. Frequently, clients request cleaning by tilting their body or remaining motionless near the surface while being cleaned (40%) however, in most cases, the interaction ends because clients flee (46%). This could mean that D. sargus is also feeding on mucus and/or living tissue. These shifts between exploitation and cooperation have been frequently described for tropical reef species. Our results support cooperative behaviour, with a clear correlation between the number of nips per cleaning event or the number of nips to which the client reacted positively and cleaning event duration (n=552; Spearman correlation r=0.79, p<0.001; r=0.76, p<0.001, respectively). Furthermore, no correlation was detected between the number of jolts by the client fish and the cleaning event duration (n=552; Spearman correlation r=0.07, p=0.105) meaning that jolting does not increase with increased interaction time. In the future, the evaluation of the ecological importance of D. sargus as a cleaner species in the North-Eastern Atlantic, should proceed with field observations in different habitats and a detailed juvenile diet analysis. This will clarify the geographic expression of cleaning behaviour in this species and the relative importance of ectoparasites in their diet. These results are also useful to call the attention to the potential use of juvenile D. sargus as cleaners in marine temperate aquaculture fish farms.
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