Their distinctive orange and white colours make clownfish one of the most recognisable marine species, but new research has found the bright hues may also be a mechanism to keep younger individuals out of trouble.
The youngest and smallest fish appear brighter under ultraviolet light than mature, more dominant fish.
"To our eye, we won't pick up on this because we're not ultraviolet sensors but to these fish — we were able to calculate this — this would be fairly conspicuous," Laurie Mitchell, a researcher from the University of Queensland, said.
Dr Mitchell was part of a team that studied the colouration of a population of Great Barrier Reef anemonefish from Dyiigurra (Lizard Island) off the coast of far north Queensland.
The research, published this month in the journal Behavioral Ecology, analysed the behaviour of fish in aquarium chambers with and without filters that block the UV-reflection of the anemonefish skin.
Pitting the fish against one another in contests using different filters, the researchers were able to establish the more reflective fish were treated as subordinate while the less reflective individuals were viewed as dominant.
It is one of very few studies into the function and purpose of the clownfish colour pattern.
Vulnerable fish risk 'death sentence'
Also known as anemonefish because they live symbiotically with stinging sea anemones, clownfish exist in what Dr Mitchell described as a "strict social hierarchy based on body size".
"If they are not accepted, it could be essentially a death sentence for them if they get evicted from the anemone," Dr Mitchell said.
"There are a lot of reef predators around and a little anemonefish makes quite an easy snack."
Dr Mitchell said conflict between clownfish is quite rare but can occur when an individual attempts to move into an anemone that is already home to a group of fish.
If the new arrival is sufficiently subordinate, the adult fish will allow them to stay and have shelter.
"That's where it's really important for [the new fish] to be able to communicate effectively that they are submissive and are not trying to challenge the status quo," he said.
"At least not yet."
Despite the findings of the study, scientists still have other hypotheses about the function and purpose of the distinctive skin, and more research is needed to be definitive.
The explanations probably aren't mutually exclusive.
The colouring may help the 28 different species of anemonefish distinguish between one another, for instance, or even act as a warning.
"The anemone has a toxic sting and, pair that together with the anemonefish's colours, it could be quite a good warning colouration for predators to learn to avoid," Dr Mitchell said.
"But in terms of actually testing these ideas, there hasn't really been many [studies]."
