Gobioid fishes commonly feed on invertebrates. Epiben-thic species feed on crustaceans, small worms, and insect larvae associated with the benthos. Some coral-dwelling gobies, such as gobiodontines, feed on the polyps of the corals on which they live. Nektonic species living in the water column, such as the glass goby (Gobiopterus chuno) from fresh and brackish waters of Asia, feed on plankton. Large eleotrid gobies may feed on other, smaller fish. Various gobioid fish species are specialized for grazing on algae. Sicydiine gobies, such as oopo alamoo have rows of fine teeth that are ideal for scraping algae off rock surfaces. Some algal feeders have
elongate, elaborately coiled guts to assist in the digestion of the tough algal material, e.g., species of Chlamydogobius from Australia and Kelloggella from the Western Pacific. "Cleaner" gobies, such as the seven-spine, gobiosomine gobies (e.g., Go-biosoma genie and the neon goby Elacatinus oceanops) are specialized feeders that pick parasites off the scales and skin of other fish, sometimes entering the mouth and gills to extract food items. Another seven-spine goby, the nineline goby (Ginsburgellus novemlineatus) shelters on rocks beneath the test, or outer skeleton, of the sea urchin (Echinometra locunter) and feeds on the tube feet of the urchin.
The small size of many gobioid species allows them to exploit meiobenthic food resources that are too small for other species. The small size of the gobies might also put them below the threshold for attack by some large, predatory fishes. However, the small size also places the fish at risk from a variety of other predators. For example, coral-dwelling gobiid species of Eviota less than 1.2 in (30 mm) long may be eaten by slightly larger coral-dwelling cardinalfishes 1.8-2.1 in (45-53 mm) long. The nineline goby, which hides under sea urchins, can fall prey to long-snouted predators like trum-petfishes, that can delve between the spines of the urchin. Large invertebrates, such as shrimps, can overpower small fishes, and there is a reported case of a small goby being ingested by the nemertean worm Lineus longissimus. Small reef-dwelling gobies regularly fall prey to piscivorous mollusks of the genus Conus. Freshwater gobioids are regularly preyed upon by water snakes and fish-eating birds.
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