octopus
鮹 centers on the octopus, a sea creature with a soft body and eight arms.
鮹 combines 魚 (fish) with 肖, which likely contributes the sound. The character was created to represent the octopus as a fish-like sea creature.
The left side 魚 means fish, and the right side 肖 looks like a small body with arms. Picture a fish-like creature with many arms: an octopus.
For ショウ, imagine a show where an octopus performs tricks: show -> ショウ, and the octopus is the star of the show.