In the weird and wonderful world of bacteria, it sometimes seems best to expect the unexpected. Take their size, for instance.
Most bacteria are only a few micrometers, or millionths of a meter, long.
But in the warm waters of the Red Sea, and off the coast of Australia, the largest bacteria ever seen have been discovered in the guts of a fish. Epulopiscium fischelsoni is a bacterium of mammoth proportions. It can sometimes grow as large five hundred micrometers, or as about the size of the period at the end of this sentence, which is a remarkable size for bacteria. These surgeonfish live in and around coral reefs, feeding on the algae and plants that grow there. When researchers studying the fish looked into their guts, they found tens of thousands of these bacteria there.