the mullet
魛 refers specifically to the mullet, a type of fish. The meaning is narrow and concrete, centered on this particular fish species.
魛 combines 魚 (fish) with 刀 (knife), likely chosen for its sound to name the mullet. The exact historical reasoning behind this specific combination is uncertain.
A fish 魚 with a knife-like shape 刀: picture a mullet with a sleek, blade-like body cutting through the water.
For トウ, imagine a mullet leaping out of the water and landing on the toe of a fisherman: toe -> トウ, and the fish is a mullet.