Yes, it’s true! Parrotfish really do create islands with their poop! But this family reaches even crazier realms of the bizarre…
Parrotfish are extremely diverse globally and vary morphologically, behaviourally, reproductively and developmentally according to geographic location.
They’re renowned for their characteristic dentition, which distinguishes them from other Labrids. Their teeth are arranged externally to their jaw, forming a beak-like structure, which they use to remove algae and detritus from substratum, for example coral, creating the definitive ‘crunch’ you can often hear whilst diving in parrotfish biomes. The parrotfish then absorb the nutrients they need from the coral and the remaining waste is excreted as fine sand, which helps to build islands!
Parrotfish are found primarily in shallow, sub tropical/tropical areas, adjacent to coral reefs. We can see plenty at Dibba Rock! Nonetheless, some species are also found in sea grasses and rocky substrates, these species are known for their free imbricate (overlapping) teeth and modified dental and muscular structures, allowing them to feed on rocky substrates.
Most species of parrotfish are very colourful, furthermore some species exhibit sexual dichromatism (displaying two distinct colour phases). Distinct colour phases were often considered as different individual species rather than a singular species, but we now recognise these fish as dichromatic individuals. These changes in coloration are also linked with changes in size, shape and sometimes gender!
Complex socio-sexual systems have been observed in particular genera of parrotfish, whereby juveniles may be dull colours, until they mature displaying vibrant colours during an ‘initial phase’, prior to maturing into a ‘terminal phase’ male, exhibiting bright colours presenting their dominant reproductive activity. Some monchromatic (single coloured) species metamorphose (from juvenile to adult) as female and change sex when necessary! Changes of sex from male to female is known as protandry and are less common than the change from female to male, known as protogyny.
However to make matters even more interesting parrotfish have been known to display colour changes associated with behaviour, such as excitement to diurnal rhythm (internal processes). Although this is not yet fully understood, it has been suggested these changes could be linked to body length. The change throughout growth stages was predicted to be accompanied by an activation and an inactivation of genes.
So there we have it! Colour changing, sex changing, crazy dental set-ups and sand pooping fish!