Passage 10.9.4
καὶ ὁ μὲν δῆλα τοῖς ἐν τῇ πόλει Κορκυραίοις ἐποίησεν· οἱ δὲ---ἑλεῖν γὰρ τοὺς θύννους προαιρούμενοι τὴν ἄλλως ταλαιπωρίαν εἶχον---θεωροὺς ἀποστέλλουσιν ἐς Δελφούς· καὶ οὕτω Ποσειδῶνί τε ἐκεῖνον θύουσι τὸν ταῦρον καὶ αὐτίκα μετὰ τὴν θυσίαν αἱροῦσι τοὺς ἰχθῦς, καί σφισι τὸ ἀνάθημα ἐν Ὀλυμπίᾳ τε καὶ ἐν Δελφοῖς ἐστιν ἡ δεκάτη τῆς ἄγρας.
And he thus made his power clear to the inhabitants of the city of Corcyra. They, preferring above all else to catch the tunny fish but facing difficulties beforehand, sent envoys to consult the oracle at Delphi. Afterward, they sacrificed that specific bull to Poseidon, and immediately following the sacrifice they successfully caught the fish. In both Olympia and Delphi they dedicated a tithe of their catch as an offering.