Cleaning mutualism in an Australian estuary: silver batfish services fish clients at cleaning stations, with a summary of brackish water cleaners

Cleaning symbiosis is one of the most iconic relationships between fishes. The cleaner picks parasites and diseased tissue from the body of so-called clients. Both parties benefit from this association: the cleaner obtains food and the client has unwanted organisms and material removed. Knowledge about cleaning interactions derives mostly from tropical and temperate reefs, although this relationship also occurs in fresh and brackish water. Cleaners and their clients in brackish water are the least known, mostly due to turbidity that precludes suitable observations. About half of the studies on brackish water cleaners come from aquarium observations, and studies in nature are scarce. I report here on cleaning by silver batfish (Monodactylus argenteus) juveniles in an Australian urban estuary. This cleaner holds stable or temporary cleaning stations and services clients as diverse as mullets, bream, pufferfish and catfish. The clients solicit the cleaner's services by grouping and posing at the cleaning stations. When not engaged in cleaning the batfish pecks at periphyton, sometimes followed by a queue of clients. In addition to the description and documentation of cleaning interactions, I summarise here the knowledge about cleaners and their clients that dwell in brackish water. Ten cleaner and 16 client species sum up the knowledge about cleaning symbiosis in brackish water to date. I suggest that more instances of cleaning in this environment will come up from potential cleaners with further observational, natural history-oriented studies in estuaries under appropriate visual conditions, or aquarium observations.