This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮷 combines 魚 (fish) with 弟, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is a fish 魚, and the right side is 弟 (younger brother). Picture a younger brother fish, but its exact meaning is uncertain.
For イ, imagine an eel (イ) that looks like a fish with a younger brother shape: eel -> イ.