Symbiosis
Different strains of Epulopiscium have been isolated in most surgeonfish species around the world, and scientists have been unable to culture Epulopiscium outside of its natural habitat, meaning that the relationship between the two is probably mutually beneficial and symbiotic.
The daily life cycle of Epulopiscium exhibits a correlation with the daily activities of the surgeonfish. During the day, when the surgeonfish feed on algae, the bacteria's compact, spherical nucleoids migrate to the poles of the cell and begin to elongate. As the day goes on, the average length of the cells increase, until the nucleoids make up a large percentage of the parent cell volume, and the sporulation process begins in the late afternoons and evenings, when these nucleoids reach a maximum of approximately 50–75% of the length of the parent cells. The pH of the surgeonfish's gut also shows a correlation with the daily life cycle of the bacteria, showing that they suppress it during the day.
Although the exact biochemical nature of the symbiosis remains unclear, it is safe to assume that the bacteria assist the fish in breaking down algal nutrients. Many bacteria of the genus Clostridia are gut symbionts in a variety of other species, including humans, usually involved in breaking down complex carbohydrates.
Read more about this topic: Epulopiscium Fishelsoni