Cleaner fish are potential super-spreaders

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Abstract [Related publication]:

Cleaning symbiosis is critical for maintaining healthy biological communities in tropical marine ecosystems. However, potential negative impacts of mutualism, such as the transmission of pathogens and parasites during cleaning interactions, have rarely been evaluated. Here, we investigated whether the dedicated bluestreak cleaner wrasse Labroides dimidiatus, is susceptible to, and can transmit generalist ectoparasites between client fish. In laboratory experiments, L. dimidiatus were exposed to infective stages of three generalist ectoparasite species with contrasting life-histories. Labroides dimidiatus were susceptible to infection by the gnathiid isopod, Gnathia aureamaculosa, but significantly less susceptible to the ciliate protozoan, Cryptocaryon irritans, and the monogenean flatworm, Neobenedenia girellae, compared to control host species (Coris batuensis or Lates calcarifer). The potential for parasite transmission from a client fish to the cleaner fish was simulated using experimentally transplanted mobile adult (i.e., egg-producing) monogenean flatworms on L. dimidiatus. Parasites remained attached to cleaners for an average of two days, during which parasite egg production continued, but was reduced compared to control fish. Over this timespan, a wild cleaner may engage in several thousand cleaning interactions, providing numerous opportunities for mobile parasites to exploit cleaners as vectors. Our study provides the first experimental evidence that L. dimidiatus exhibits resistance to infective stages of some parasites yet has the potential to temporarily transport adult parasites. We propose that some parasites that evade being eaten by cleaner fish could exploit cleaning interactions as a mechanism for transmission and spread.

Data methods:

In laboratory experiments, we first test the susceptibility of L. dimidiatus to three generalist parasites with contrasting life-histories. To do so, we exposed 20 L. dimidiatus and 20 control individuals (Coris batuensis or Lates calcarifer) to infective stages of a species of gnathiid isopod Gnathia aureamaculosa, a species of monogenean flatworm Neobenedenia girellae and a species of ciliate protozoan Cryptocaryon irritans. We then test whether adult N. girellae remained attached and produced viable eggs when transferred to the skin of live Lab. dimidiatus by manually transplanted adult N. girellae from a donor host to L. dimidiatus. Finally, we test for how long adult N. girellae could survive on L. dimidiatus after being manually transplanted. All data analyses were performed in R version 4.0.2 (R Core Team 2020)
The full methodology is available in the publication shown in the Related Publication link below.

Software/equipment used to create/collect the data: Excel version 2205

Software/equipment used to manipulate/analyse the data: R Studio 2021.09.0