Labroides dimidiatus is a well-known species of cleaner fish, while there are not many observation records on cleaning behavior of Plotosus japonicus. In this study, cleaning behavior of P. japonicus and L. dimidiatus was observed in a large aquarium tank (approximately 1000 m3 in capacity) at the Enoshima Aquarium to examine the relationship between their cleaning behavior and client fishes’ requesting behavior. P. japonicus was observed to perform cleaning behavior on 32 client species, some of which (17 species) displayed requesting behavior to P. japonicus. A total of 53 client species were recorded for L. dimidiatus, many of which (26 species) displayed requesting behavior to L. dimidiatus. We confirmed that in addition to L. dimidiatus, P. japonicus and some client species also developed their relationship through symbiotic coactions.
