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(Gobius ophiocephalus), a fish of the family Gobiidae. The laterally compressed body measures up to 25 cm in length and weighs up to 75 g. The grass goby is distributed in the Mediterranean and Black seas, in the Sea of Azov, and in the Atlantic Ocean, near the Strait of Gibraltar. It lives in thickets of green algae. The fish, which attains sexual maturity in the second year of life, spawns in the spring. The male builds a nest of algae, into which five to ten females deposit their eggs, which the male, after fertilization, guards. The fecundity is 9,000 to 52,000 eggs. The grass goby feeds on invertebrates and small fishes. It is of commercial importance.