bream
鮉 centers on a specific fish: the bream. It is a narrow, concrete term without broader abstract extensions.
鮉 combines 魚 (fish) with 召, which likely contributes the sound. The character was created to name a specific fish, the bream.
The left side is a fish 魚, and the right side 召 looks like a call to summon. Imagine summoning a bream from the water: the fish answers the call.
For チョウ, picture a bream leaping out of the water and landing with a distinctive 'choh' sound, like a name: Chou the bream. Chou -> チョウ.