anchovy
鱄 centers on a specific small fish: the anchovy. The meaning is narrow and concrete, with no clear abstract extensions.
鱄 combines 魚 (fish) with 專, which likely contributes the sound. The character was created to name a specific fish, the anchovy.
The left side is a fish 魚, and the right side 專 looks like a specialized tool. Imagine a fish so specialized it's only used for anchovies.
For セン, picture a thousand (千, せん) tiny anchovies swimming together: 千 -> セン, and the fish radical reminds you it's a fish.