A Roman mosaic depicting a fish. You can find more on fishes here: fauces mosaic, sea monster fauces mosaic, marine style vessel, fish and squid, an ugly fish from Ostia, marine fresco, fish mosaic from the baths of Caracalla, a dophin from Ostia.
"Auguries are also derived from this department of Nature, and fishes afford presages of coming events. While Augustus was walking on the sea-shore, during the time of the Sicilian war, a fish leapt out of the sea, and fell at his feet. The diviners, who were consulted, stated that this was a proof that those would fall beneath the feet of Cæsar who at that moment were in possession of the seas-it was just at this time that Sextus Pompeius had adopted2 Neptune as his father, so elated was he with his successes by sea."
Pliny the Elder - Naturalis Historia (the Natural History) IX.22
Translated by John Bostock, H.T. Riley