Oppian who lived around the time of Marcus Aurelius wrote a poem on fish called Halieutica. Perhaps not a promising theme for a 3500 line poem and probably not the pinnacle of literature though a strangely enjoyable read. Here he shows that as now dolphins were thought to have a special relationship to men.
οἱ δ᾽ ἦ τοι πάντες μέν, ὅσοι ναίουσι θάλασσαν
ζωοτόκοι, φιλέουσι καὶ ἀμφιέπουσι γενέθλην,
δελφίνων δ᾽ οὔπω τι θεώτερον ἄλλο τέτυκται:
ὡς ἐτεὸν καὶ φῶτες ἔσαν πάρος ἠδὲ πόληας
ναῖον ὁμοῦ μερόπεσσι, Διωνύσοιο δὲ βουλῇ
πόντον ὑπημείψαντο καὶ ἰχθύας ἀμφεβάλοντο
γυίοις: ἀλλ᾽ ἄρα θυμὸς ἐναίσιμος εἰσέτι φωτῶν
ῥύεται ἀνδρομέην ἠμὲν φρόνιν ἠδὲ καὶ ἔργα.
Of all the creatures who dwell in the sea and give birth to live young and love and care for their offspring, none has been created more divine than the dolphin. In truth they were once men and lived in cities like humans but by the will of Dionysius they exchanged land for sea and they put a fish-like nature on their limbs. Yet still the righteous spirit of men keeps their thought human and their deeds also.