Small reef fish with “eye” spots on their rear fins use these spots to escape predators, according to Australian researchers with the ARC Center of Excellence for Coral Reef Studies. The scientists say that Ambon damselfish (Pomacentrus amboinensis) grow a larger false eye spot on their rear fins and then reduce the size of their real eyes in an effort to potentially confuse predators by looking as if they are swimming in the opposite direction, according to Arc Center researchers.
Their research, published in the journal Nature and led by Oona M. Lonnstedt, shows that the juvenile Ambon damselfish that have large spots on their rear fins have a survival rate that is five times higher than that of fish with a normal spot. They conducted their study on the reef as well as in the laboratory. The juvenile damselfish were placed in a specially built tank where they could see and smell a dusky dottyback (Pseudochromis fuscus), a fish known to prey on the juvenile Ambon damselfish. When this occurred, the damselfish grew its eyespot bigger while shrinking its actual eyes. When subjected to the white-barred goby (Amblygobius phalaena), a herbivorous fish, there was no such enlargement of the eye spots.
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On the reef, the fish were placed on a patch reef, away from the main reef with Pocillopora damicornis corals, a coral in which the fish were known to settle. They were then observed twice each day for a total of four days and were assumed caught by predators when they went missing from the patch reef. The researchers also implemented cage controls that enabled fish to swim away and found that there was no movement from the patches, suggesting that there was no migration to the larger nearby reefs. The scientists speculate that not only does the eye spot confuse the predator fish, it also leads any potential attack away from the head area and to the tail.
The full report, “Predator-induced changes in the growth of eyes and false eyespots” can be found here. The authors of the report are Oona M. Lönnstedt, Mark I. McCormick, and Douglas P. Chivers.