Indonesia houses some of the most biodiverse reefs in the world, with thousands of species of fish for scientists to study and observe. With such a huge variety of species populating the reef, it’s little wonder that some of them might exhibit bizarre and amazing behaviour.

One such species is the convict blenny or engineer goby (Pholidichthys leucotaenia), an eel-like fish that gains its name from its distinctive black and white stripes. The stripes are only sported by the juveniles, while the adults look so different that they almost resemble an entirely different species altogether. Long, dark and eel-like, the adults are very reclusive and spend all their time hidden in burrows under the sand.

For a long time the adults’ food source remained a mystery and it was suspected that they survived by cannibalism on the young. But then juveniles were seen to swim in and out of the adults mouths unharmed, so the study continued until it discovered the bizarre truth. When the stripy juveniles leave the burrow to feed in huge swarms, they return at night to suspend themselves from the ceiling by mucous threads extending out from pores in their heads. Whilst dangling, the juveniles then regurgitate partially digested plankton to the adults – the very opposite of bird feeding behaviour.

As if that wasn’t bizarre enough, the juvenile convicts have also been observed mimicking the much more dangerous and venomous striped catfish (Plotosus lineatus). Known as “Batesian Mimicry”, this type of impersonation is a very useful ploy by harmless species to gain protection from would-be predators by pretending to be much more harmful than they really are.

Thank you for reading this week's edition of FIN ('Fascinating Ichthyological Nugget'): the easiest way to propel your aquatic knowledge! We sincerely hope that you'll find these of interest and want to share them with your friends…