blowfish
鯸 centers on the blowfish, a specific type of fish. The meaning is narrow and refers directly to that animal.
鯸 combines 魚 (fish) with 侯, which likely provides the sound. The character was created to name the blowfish specifically.
The left side 魚 means fish, and the right side 侯 looks like a puffed-up nobleman. Picture a blowfish puffing itself up like an arrogant lord.
For コウ, imagine a blowfish puffing up and letting out a loud 'koh!' sound as it inflates: koh -> コウ.