JOHN READER / SCIENCE PHOTO LIBRARY JOHN READER / SCIENCE PHOTO LIBRARY
Territorial fish. Two male fish (Tilapia grahami or Oreochromis alcalicus grahami) posturing in a territorial display in a lake. They are using open-mouthed threat postures, possibly generating pressure waves to defend their 40-centimetre-wide territories. These fish are a type of cichlid that inhabit warm, alkaline freshwater lakes in eastern central Africa. They breed there all year round and the males are fiercely territorial. They feed actively in the evening on invertebrates at the surface, reaching sizes of around 20 centimetres in length.
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