1. Plankton: Moorish idol fish primarily feed on planktonic organisms, including zooplankton (small animals) and phytoplankton (tiny algae). They swim with their mouths open, filtering these plankton out of the water.
2. Algae: They also graze on algae that grow on coral reefs and rocks. They use their small, brush-like teeth to scrape algae off the surface of these structures.
3. Small invertebrates: The Moorish idol fish also consumes small invertebrates, such as crustaceans (shrimp, crabs) and mollusks. They use their pointed snouts to probe crevices and holes in the reef in search of these prey items.
4. Coral: Moorish idols have been known to nibble on coral polyps, although it's not a significant part of their diet. They mainly feed on the mucus and algae that cover the surface of corals rather than the coral itself.
5. Detritus: In addition to the above, the Moorish idol fish may also feed on detritus, which consists of organic matter and particles suspended in the water column.
The Moorish idol fish plays an essential role in maintaining the health of coral reef ecosystems. By consuming algae and plankton, they help to control their populations and prevent overgrowth that could smother and damage the corals. Their diet also contributes to nutrient cycling within the reef environment.