In a recent issue of the journal of Natural History, biologists from Australia and Brazil have discovered and described an instance of an octopus mimicking a fish.
Joao Krajewski and coauthors studied and recorded the interaction between the octopus Octopus insularis and the grouper Cephalopholis fulva in dives over a period of five years in the Fernando de Noronha Archipelago, about 350 km off the coast of northeast Brazil, tropical west Atlantic.
The authors recorded 39 octopus individuals being followed by 1"14 grouper individuals, of which most of the octopus (33) were followed by five or more fish and always remained in the centre of the group of fishes.
Although the octopuses remain camouflaged when resting on the bottom, they became similar in shape and colour to the fish when swimming backwards with the fishes, rendering the octopuses inconspicuous.
The authors also recorded 12 octopus individuals not followed by fishes. Again, they were camouflaged when resting on the bottom, but assumed a bicoloured pale and dark pattern similar to those displayed by foraging grouper when swimming backwards via jet propulsion.
The authors hypothesize that this pattern of beahviour and colour change in the octopus is a form of mimicry that renders it inconspicuous to visually-oriented predators.
The authors continue, dditionally, when seen from close to the bottom, a view that most benthic predatory fish (e.g. morays, snappers and grunts) have, the octopuses recorded here were even more inconspicuous because they were always in the centre of a group of fish with similar colour/contrast and shape to themselves.
For more information, see the paper: Krajewski, JP, RM Bonaldo, C Sazima and I Sazima (2009) Octopus mimicking its follower reef fish. Journal of Natural History 43: 185"190.