Here are a few possibilities, depending on your interpretation:
* Direct Opposite (Sound): There isn't a direct opposite sound to "aye-aye". It's a specific phrase, not a singular sound.
* Opposite Meaning (Affirmation): The opposite of "aye-aye" (meaning "yes" or "affirmative") would be "nay" or "no".
* Opposite Animal: "Aye-aye" refers to a specific lemur species. Its opposite could be any other animal, depending on the criteria you're using to define "opposite" (e.g., size, habitat, behavior, etc.).
Could you please clarify what you're looking for?