This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鰙 combines 魚 (fish) with 若, which likely contributes the sound. The exact historical development is uncertain.
The left side is a fish 魚, and the right side is 若. Since the meaning is unclear, picture a rare, mysterious fish that looks young and fresh like the 若 component suggests.
For ハヤ, imagine a fast-swimming fish darting through the water with a sharp 'haya!' sound: haya -> ハヤ.