sturgeon
鱘 centers on a specific large fish: the sturgeon. It is a narrow, concrete term without broad abstract extensions.
鱘 combines 魚 (fish) with 尋, which likely contributes the sound シン. The character was created to name the sturgeon specifically.
The left side 魚 is a fish, and the right side 尋 looks like a hand with a measuring tool. Imagine a fisherman measuring a huge sturgeon he just caught.
For シン, picture the shiny skin of a sturgeon: shin -> シン, and the fish's gleam helps you remember the reading.