This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鯘 combines 魚 (fish) with 委, which likely contributes the sound. The exact historical development is uncertain.
The left side is a fish 魚, and the right side is 委. Without a clear meaning, picture a fish that has been entrusted (委) to someone, but its purpose is unknown.
For ダイ, imagine a fish that is entrusted to a diver (ダイバー): diver -> ダイ, and the fish is passed along.