Goatfish or goatfishes?11 September 2017
This is a picture of schooling goatfish. In fact, when you have a closer look it is a school of goatfishes, because there is more than one species present. The one with the blue stripes is the Indian mimic goatfish (Mulloidichthys ayliffe). This species mimics, and also aggregates with, Bluestripe snappers (Lutjanus kasmira). The Bluestripe snapper is known to aggregate with Yellowfin goatfish (M. vanicolensis), the other goatfish species in the picture.
I took this photo years ago during a dive on the east coast of South Africa. On that dive I saw that the three species mentioned above formed heterospecific shoals that either desintegrated into loose aggregations or became tight schools. Schools were formed especially when a predator (or some other threat) was around, and they prefered their own species to do so. When the danger had passed the fish fanned out again. Although the mimics did aggregate with the Bluestripe snappers, whenever schools were formed they preferred the Yellowfin goatfish to form schools with. There were also very few mimics in comparison to the snappers and certainly compared to the abundant Yellowfin goatfish.