Why does a Caribbean angelfish sometimes resemble its Indo-Pacific cousin, even though they have never lived in the same ocean? Why do coral reefs harbour such a wide range of stripes, spots and patterns? A study conducted by theUniversity of Liège y reveals that this explosion of colour patterns is not the result of chance. The more species a reef is home to, the more varied the patterns, and fish from different oceans often end up looking alike, guided by the same deep biological constraints.
Coral reef fish are among the most colourful animals on the planet. Horizontal or vertical stripes, round or eye-shaped spots, saddle or labyrinthine patterns... their visual diversity is breathtaking. But this explosion of patterns and colours is not the result of chance. For a long time, scientists wondered about the origin of this diversity, asking themselves whether it was the result of local ecological pressures (each ocean shaping its own diversity of pigmentation patterns) or whether it followed more universal evolutionary laws.
To answer this question, Bruno Frédérich and his colleagues analysed the pigmentation patterns of 918 species belonging to six large families of reef fish: surgeonfish ( Acanthuridae ), butterflyfish ( Chaetodontidae ), snappers ( Lutjanidae ), mullets ( Mullidae ), angelfish ( Pomacanthidae ) and damselfish ( Pomacentridae ). By systematically coding thirty different pattern types on photos of each species, the researchers compiled a unique database covering the five major biogeographic regions of the globe: the Atlantic, the Western Indian Ocean, the Central Indo-Pacific, the Central Pacific and the tropical Eastern Pacific.
The more species there are, the more varied the colour patterns
"The most striking initial finding is that we were able to link colour pattern diversity to the number of species present in a region," explains Bruno Frédérich, an evolutionary biologist at ULiège . The more species an ocean is home to, the more different patterns it contains. This finding suggests that speciation—the process by which new species appear —and the importance of visual recognition of conspecifics play a major role in the diversification of patterns, more so than local environmental conditions."
But the most surprising result obtained by the scientific team concerns the evolutionary dynamics of these patterns. "They evolve very quickly, but within a limited space," says the researcher. In other words, reef fish quickly explore the available decorative possibilities, but these possibilities are constrained by the biological mechanisms that produce colours and patterns. This combination of speed and constraint explains why species that are not closely related, living in different oceans, sometimes end up sporting visually similar motifs. This is called evolutionary convergence."
Patterns shaped from within
How can these evolutionary constraints be explained? Researchers point to cellular and developmental processes that govern the formation of pigmentation patterns. Patterns are not only shaped by the environment or predators, but also by biological 'internal rules' that limit the range of possible forms. Thus, across the oceans, reef fish converge on the same visual solutions, not because they are subject to exactly the same external pressures, but because they share similar developmental mechanisms.
This work is in line with research conducted by the ULiège's Laboratory of Evolutionary Ecology, which had already explored the evolution of colour patterns in clownfish . It opens up new perspectives for understanding the underlying mechanisms that generate and structure this visually striking facet of biodiversity. By mapping the pigmentation pattern diversity of nearly a thousand species on a global scale, this study provides an important answer: the colour patterns of reef fish are not simply a reflection of their local environment, they tell an evolutionary story shaped by speciation, convergence and deep biological constraints.
BMC Biology
Rapid and repeated evolution of pigmentation patterns in reef fishes
23-Feb-2026