Haemulon

Haemulon, commonly called scaled-fin grunts, is a genus within the grunt family. Its members are mostly native to the western Atlantic, though a handful of species live in the eastern Pacific. In Brazil, this genus is regarded as especially significant to coral reef ecosystems, both because of its commercial importance and its essential ecological functions.

Description

The genus contains roughly 23 species. These fish have an oblong body shape and a large mouth.

A distinctive feature is the presence of scales covering the rays of the second dorsal and anal fins, and the second spine in the anal fin is longer than the third. The interior of the mouth is typically bright red. While juvenile Haemulon look very similar across species, adults vary greatly in appearance.

Diet

Most Haemulon species feed on small prey found on the seabed, though some eat plankton in open water. Like other grunts, they are nocturnal: around sunset, they leave the shelter of the reef in schools to hunt. The schools break apart as individuals forage, then reform near dawn to return to the reef.

Behaviour

These fish are common in shallow reef communities. Their schools can number in the hundreds or thousands and include both adults and juveniles. Schools often contain multiple Haemulon species—for instance, H. squamipinna and H. aurolineatum may mix together. Haemulon have also been observed schooling with grunts from other genera, such as Anisotremus virginicus, and with fish from other families, including the snapper Lutjanus alexandrei, the goatfish Pseudupeneus maculatus, and the jack Carangoides bartholomaei.

Other fish join large Haemulon schools for protection. Some simply benefit from the safety of a large group, but others engage in protective mimicry: unrelated fish that resemble Haemulon in color, size, and shape join the school to evade predators, copying the swimming style, movements, and postures of the grunts. Examples include the goatfish Mulloidichthys martinicus, the parrotfish Sparisoma axillare, and the herring Harengula clupeola. M. martinicus, in particular, stays with its own kind while sheltering in the reef, but when it moves into open water where it is more visible to predators, it tends to join schools of Haemulon chrysargyreum, which it closely resembles, adopting the grunt’s posture to blend in.