This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮼 is a rare character combining 魚 (fish) with a phonetic component (⿱⿰ヨ又冖). The exact historical development is uncertain.
Since the meaning is unclear, picture a mysterious fish (魚) with an unusual shape on the right, like a fish that defies easy description.
For シン, imagine a rare fish with a shiny (シン) scale pattern: shiny -> シン, and the fish (魚) sparkles.