This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮻 combines 魚 (fish) with 夋, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is 魚 (fish), and the right side is 夋. Without a clear meaning, picture a rare, mysterious fish that scholars are still trying to identify.
For サ, imagine a scholar saying 'Sa!' in surprise when they discover this rare fish: Sa -> サ.