Gregory the Dialogist

Hence again, fish that do not have fins are forbidden from being eaten by the faithful people. For fish that have scale-fins are also accustomed to leap above the waters. What therefore is figured by finned fish except elect souls? These alone indeed pass into the body of the heavenly Church, who, supported by the fins of virtues, know how to leap through heavenly desire, so that they may reach toward things above through contemplation, although they fall back again into themselves from mortal flesh.

Forty Gospel Homilies, Homily 31 ↗