These fish commonly include significant amounts of algae in their diet—in fact, the word “tang,” which is applied to smaller members of the group, is an abbreviation of the German Seetang, meaning “seaweed.” Just like land herbivores, these fish have beneficial populations of bacteria in their alimentary tracts to assist the breakdown of plant matter.
[Ebook] Encyclopedia of Aquarium & Pond Fish – Introduction to Marine Fish – Illness and treatment – Health concerns
Most marine aquarium fish are natural inhabitants of coral reefs, which are among the most stable and unchanging of all ecosystems on the planet. Many of the health problems suffered by marine aquarium fish therefore stem from fluctuations in water quality in the home tank. Maintaining suitable water conditions will keep the fish in the best condition to repel pathogens and parasites.