Anvil use by three wrasse species: Halichoeres hortulanus , Thalassoma jansenii, and Thalassoma lunare

Over the past few decades, tool use has been described in a variety of animals across taxa. However, there are relatively limited reports and studies of tool use in marine environments. Among marine fish though, labrids have been reported to be proficient at using tools. Here, we describe the first observations of tool use in two species of tropical wrasses— Halichoeres hortulanus (checkerboard wrasse) and Thalassoma jansenii (Jansen’s wrasse)—and the first report of tool use from the wild for the wrasse Thalassoma lunare (Moon wrasse). These observations were made incidentally as part of size-specific predation assays for a small burrow-dwelling sea urchin (Echinostrephus molaris) in the Lakshadweep Archipelago, Indian Ocean. We documented multiple instances of anvil use by the wrasses H. hortulanus , and T. jansenii , and one instance of anvil use by T. lunare . All three species were recorded carrying the assay urchins to a nearby coral or benthic substrate and striking them repeatedly to break off their spines and crack their tests before consuming them. The behaviour was observed multiple times in different wrasse individuals. Also, sea urchin test size was a good predictor of the size of the fish that preyed on them. As naturalists spend more time observing fish in their natural environment, records of tool use in fish are increasing. Often these observations are incidental, yet documenting them carefully is critical, so we can ask larger questions about the evolution and development of animal intelligence. This study adds to observations of predation-associated tool use by fishes expanding reports of this behaviour taxonomically as well as geographically.