The phrase "dominion over the fish of the sea" is a metaphorical expression that means having power, control or authority over something. In this context, it refers to God's ability and rightful ownership over all the creatures living in the ocean, including fish. The phrase comes from the Bible verse Psalm 89:10 which states "You have loved righteousness and hated wickedness; therefore God, your God, has anointed you with the oil of gladness beyond your companions."