This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮋 combines 魚 (fish) with 由, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is a fish 魚, and the right side is 由. Since the meaning is unclear, picture a fish with a reason (由) for being mysterious.
For ユウ, imagine a fish (魚) swimming in a U-shaped bend: U -> ユウ, and the fish glides through the water.