At the moment, Aquaculture's Jellyfish does not have a use. Perhaps add a recipe that uses Jellyfish in it? Harvestcraft crafts Slime from Jellyfish, so that's a potential recipe.

That does sound interesting, and would add some compatibility. Perhaps add a brewing recipe to make potions of poison from jellyfish?

I like these ideas.

Furnace + Jellyfish > Slime Ball
Brewed Jellyfish > Poison (Effectively Spider Eye Replacement)

On that note, I think Leeches atm are combined with Water Bottles to make Healing Potions. We should move that to brewing when we do this.

Partially adressed in 69a481c