When Jesus called the disciples to be “fishers of men,” he was riffing on imagery from the prophets. Yahweh fishes for Israel as He gathers exiled Jews from the sea of nations in His nets.
Isaiah 60:5 gives an additional angle on the imagery. In the parallel lines at the end of the verse the “abundance of the sea” is compared to the “wealth of nations.” Here fishing is not a return from exile but a pilgrimage of nations to Zion, nations that bring treasures to adorn and maintain the house of Yahweh.
As fishers of men, the apostles don’t simply pluck out a fish here and there. The sea is teeming with life and riches, and the apostolic mission is to gather the strength and wealth of nations, so that it can all be devoted to the glory of Christ and the edification of the church.
When Augustine and Aquinas plunder Greek thought, they are fishers of men; when Christian architects learn to adapt the basilica form to Christian worship, they are fishers of men; Constantine is a big fish at the head of a large school of fish, so when he is caught, a lot comes in with him.