A few months ago, we went on a family holiday to Noumea. While snorkelling, I noticed some fascinating fish behaviour. Unfortunately, I didn’t have a camera to capture the action. This is my report:
Several members of the wrasse family (Labridae) have been observed striking bivalves on rocks in order to break the shells and eat the flesh. These include the yellowhead wrasse Halichoeres garnoti in Florida, U.S.A. (Coyer, 1995), blackspot tuskﬁsh Choerodon schoenleinii on the Great Barrier Reef, Australia (Jones et al., 2011) and orange-dotted tuskfish Choerodon anchorago in Palau (Bernardi, 2012).
Wrasses have also been observed striking other food items on rocks. Species include the sixbar wrasse Thalassoma hardwicke striking food pellets in an aquarium (Pasko, 2010), the California sheephead Semicossyphus pulcher striking purple urchins Strongylocentrotus purpuratus in California, U.S.A. (Dunn, 2016) and the blue tuskﬁsh Choerodon cyanodus striking a juvenile green turtle Chelonia mydas on the Great Barrier Reef, Australia (Harborne, 2016). The behaviour has been described as tool use because the rock has been used as an anvil (Brown, 2012).
This report describes similar behaviour in another wrasse, the graphic tuskfish Choerodon graphicus (De Vis 1885) in a new location, New Caledonia. It extends the behaviour spatially, as well as taxonomically.
On 12th July 2017 at 1130 hours, on shallow reef flats, we heard a loud cracking sound. A C. graphicus approximately 35 cm in length was hovering above a single flat rock approximately 30 cm in diameter which was attached to the ocean floor and surrounded by sand and a collection of broken shells (midden). The fish was holding a bivalve approximately 4 cm in diameter in its mouth. It suddenly rotated its body to the left then struck the bivalve forcefully on the rock. The fish repeated this action three more times at intervals of 5-6 s. It adjusted the bivalve in its mouth after each strike. The strikes made a hole in the middle of one shell. The fish darted at several smaller fishes which were watching from 1-2 m away then swam away with the bivalve in its mouth.
The fish swam approximately 8 m to a space under a group of corals (0.6-0.8 m wide). It struck the bivalve three times on a dead coral head on the ocean floor. Pieces of shell fell off the bivalve. The fish and a smaller scrounger fish (12 cm in length) pulled the flesh from these pieces and ate it. A shell midden was observed at the site of the dead coral head.
Approximately 20 m farther on, we observed a second C. graphicus (we cannot rule out the possibility that it was the first fish) approximately 35 cm in length. This fish hovered above a single flat rock approximately 30 cm in diameter, suddenly rotated its body to the left then struck a bivalve on the rock. It repeated this action four times. One shell shattered into three pieces, each of which had flesh attached to it. The C. graphicus and two smaller scrounger fishes (10-15 cm in length) pulled the flesh from the pieces and ate it. A shell midden was located at the site of the rock.
The presence of this behaviour in C. graphicus supports the hypotheses that tool use may be particularly common in the Choerodon genus (Harborne, 2016) and may be a deep-seated behavioural trait in wrasses (Bernardi, 2012). The behaviour we observed mirrors behaviour described by other authors (Coyer, 1995, Jones et al., 2011), lending weight to the argument that it is a deep-seated behavioural trait in wrasses. The observation of this behaviour in a new location suggests that anvil use in wrasses is widespread and may even be universal.
Bernardi, G. (2012). The use of tools by wrasses (Labridae). Coral Reefs 31, 39. doi: 10.1007/ s00338-011-0823-6
Brown, C. (2012). Tool use in fishes. Fish and Fisheries 13(1), 105-115. doi: 10.1111/j.1467-2979.2011.00451.x
Coyer, J. A. (1995). Use of a rock as an anvil for breaking scallops by the yellowhead wrasse Halichoeres garnoti (Labridae). Bulletin of Marine Science 57 (2), 548–549
Dunn, R. P. (2016). Tool use by a temperate wrasse, California sheephead Semicossyphus pulcher. Journal of Fish Biology 88 (2), 805-810. doi: 10.1111/jfb.12856
Harborne, A. R. (2016). Tool use by Choerodon cyanodus when handling vertebrate prey. Coral Reefs 35, 1069. doi: 10.1007/s00338-016-1448-6
Jones, A. M., Brown, C., & Gardner, S. (2011). Tool use in the tuskﬁsh Choerodon schoenleinii? Coral Reefs 30, 865. doi: 10.1007/s00338-011-0790-y
Pasko, L. (2010). Tool-like behavior in the sixbar wrasse, Thalassoma hardwicke (Bennett, 1830). Zoo Biology 29, 767–773. doi: 10.1002/zoo.20307