This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮾 combines 魚 (fish) with 妥, but the exact historical development is uncertain. It may be a phono-semantic compound, but the original meaning and component roles are unclear.
The left side is a fish 魚 and the right side is 妥, which suggests settling or peace. Without a clear meaning, picture a fish that has settled to the bottom, perhaps spoiled or rotten, hinting at the kun-reading くさ.る (to rot).
For ダイ, imagine a fish 魚 that has died and is rotting: die -> ダイ, tying the sound to the decay idea.