During underwater marine fish biodiversity surveys from December 2021 to January 2022, on Red Sea coastal coral reefs north of Jeddah, Saudi Arabia, we observed a unique feeding behavior association between blackeye thicklip wrasse (Hemigymnus melapterus) and lyretail hogfish (Bodianus anthioides) at depths between 7 and 20 m. Observations occurred on > 20 separate dives during daytime hours (10h00 to 15h30).

When the two species co-occurred, a lyretail hogfish was always closely following a blackeye thicklip wrasse while the latter was feeding (Fig. 1a). The blackeye thicklip wrasse, in its typical foraging behavior, takes a mouthful of sand and gravel from the substratum and swims upward, streaming sand from the gill openings (Randall 2013). Whenever this occurred, the associated lyretail hogfish would catch any remaining food as it fell from the gill openings of the blackeye thicklip wrasse (Fig. 1b). The blackeye thicklip wrasse processed the fossorial (i.e., benthic) prey within its mouth and pharynx for a few moments and then forcefully ejected the remaining fragments from its mouth. At this point, the lyretail hogfish would move to feed on those ejected particles (Fig 1c). Lyretail hogfish would also aggressively defend their position as the sole associated fish with the blackeye thicklip wrasse from other lyretail hogfish individuals. Based on our observations, blackeye thicklip wrasse feeding behavior appeared unchanged by the lyretail hogfish feeding association (Fig. 1 d and e). Conversely, when the lyretail hogfish was alone, it changed its feeding behavior to blowing at the benthos to uncover prey among the substrate (Fig. 1f). (Videos of all behaviors depicted in Fig. 1 are provided in Supplemental File 1.) The blackeye thicklip wrasse appeared to process substantially more substrate than the lyretail hogfish on their own. Therefore, this interspecific feeding behavior might be unilaterally beneficial to lyretail hogfish by increasing its feeding efficiency with no notable impact on feeding the blackeye thicklip wrasse.

Fig. 1
figure 1

Associated feeding behavior between blackeye thicklip wrasse (Hemigymnus melapterus) and lyretail hogfish (Bodianus anthioides): lyretail hogfish closely following a blackeye thicklip wrasse (a); lyretail hogfish trying to catch the food particles from the sand stream from the blackeye thicklip wrasse’s gills (b) and particles ejected from the mouth (c). Individual feeding behavior of the blackeye thicklip wrasse (d and e) and of the lyretail hogfish without the associated blackeye thicklip wrasse (f). All photos were adjusted to improve the exposure; original, unedited photos and videos depicting these behaviors are available in Supplemental File 1

Given the large and overlapping distributions of these two species throughout the Indo-Pacific region (Gomon 2006; Randall 2013), further observations in a larger geographic scope could confirm whether this interspecific feeding behavior association appears elsewhere. Investigations of gut contents could reveal whether the feeding association influences dietary composition for the lyretail hogfish. More broadly, comparing populations with and without the presence of blackeye thicklip wrasse could determine the influence of the association on the fitness of the lyretail hogfish (e.g., using individual fitness metrics or population densities).