Homologous Structures
All fish have a mucus membrane surrounding their scales. The mucus usually contains high amounts of lipids and glycoproteins; however, the family Pomacentridae (anemone fish) have a special adaptation where the mucus coating the species is a great deal thicker. Also the protective layer lacks a specific substance that triggers nematocysts (the stings of an anemone); this allows the fish immunity against the toxic stings. Little is known about the mucus except that it is a genetically inherited trait and passed through the generations of each species. In other families of fish, the mucus is used as protection against harmful bacteria, an osmotic regulator and also aids the fish in nest making. The difference in mucuses has led to the divergent path of anemone fish and other species.
Read more about this topic: Ocellaris Clownfish
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