This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
魪 combines the fish radical 魚 with the phonetic component 介. The exact historical development is uncertain, but it likely represents a type of fish.
The fish radical 魚 suggests a fish, and 介 can be thought of as a shell or armor. Imagine a flatfish like a flounder that looks like it is wearing armor on the sea floor.
For カイ, picture a flatfish swimming in the Kai (カイ) sea, its body blending with the sandy bottom.