This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鰦 combines 魚 (fish) with 茲, which likely contributes the sound. The exact historical development is uncertain.
The fish radical 魚 suggests a connection to fish, but the overall meaning is unclear. Imagine a rare, mysterious fish whose name is written with this kanji.
For シ, picture a rare fish swimming in the sea: sea -> シ, and the fish radical 魚 reminds you it's a fish.