The yellowtail surgeonfish cannot fend off its enemies as well as its other surgeonfish cousins since the bladelike scalpels at the base of its tail are reduced to two or three bony plates with ridges running down the middle. These spines don't work as well to discourage predators and fishermen from biting them or grabbing them by the tail. Large schools of yellowtails graze on shallow reefs. They use their teeth to scrape short tufts of algae off rocks. Each tooth has small rounded cusps that help them scrape. Surgeonfish and other plant grazers in the sea keep the algae closely trimmed, like a lawn. Marine biologists have protected some rocky areas from surgeonfish by putting wire mesh over them. After a few weeks, long strands of red, brown, and green algae grow there because they are not being constantly cropped by the fish. The yellowtail surgeonfish also has a long complex intestine for digesting plant material. Recently, surgeonfish have been found with very large single-celled organisms living in their guts. These single-celled creatures probably help the surgeonfish digest the resistant walls of the plant cells the surgeonfish likes to eat.