Size-dependent feeding association of two wrasses (genusPseudolabrus) with the morwong,Goniistius zonatus

While foraging on the substrate, two closely-related wrasses,Pseudolabrus eoethinus andP. sieboldi, which occur sympatrically in the Uwa Sea, Shikoku Island, Japan, often accompanied the morwong,Goniistius zonatus, eating benthic invertebrates flushed out by the latter's feeding activities. Both wrasses tended to feed more frequently in such an association than when solitary.Pseudolabrus eoethinus (9–17 cm TL) accompaniedG. zonatus more frequently than the smallerP. sieboldi (7.5–12 cm TL), large individuals of the former attending the host more often than smaller ones. This tendency was not apparent inP. sieboldi. The size-dependent association frequency was determined by 1) the chances of encountering a host, and 2) interference among the wrasses. The frequency of encounter of wrasses with a host depended on the home range size of the former, such being positively correlated with body size. Interference among the wrasses resulted in smaller individuals being repelled by larger ones, irrespective of species, when they were approaching or attending a host.