The Deipnosophists (1.11)

But Phanias says that Philoxenus of Cythera, a poet, being exceedingly fond of eating, once when he was supping with Dionysius, and saw a large mullet put before him and a small one before himself, took his up in his hands and put it to his ear; and, when Dionysius asked him why he did so, Philoxenus said that he was writing Galatea, and so he wished to ask the fish some of the news in the kingdom of Nereus; and that the fish which he was asking said that he knew nothing about it, as he had been caught young; but that the one which was set before Dionysius was older, and was well acquainted with everything which he wished to know. On which Dionysius laughed, and sent him the mullet which had been set before himself. And Dionysius was very fond of drinking with Philoxenus, but when he detected him in trying to seduce Galatea, whom he himself was in love with, he threw him into the stone quarries; and while there he wrote the Cyclops, constructing the fable with reference to what had happened to himself; representing Dionysius as the Cyclops, and the flute-player as Galatea, and himself as Ulysses.