Just go to eldrich zone on crystal isles and look for big bubbles that have some black clams/oysters inside of them, put your angler fish inside the bubble, harvest, and enjoy the best black pearls harvester in the entire game, super easy, rank up for people to see this.
You can find these easily in the space biome on Genesis 2. Wait until the biome has dark grey/black asteroids with big light green/pink balls floating around (ignore the colour bit cos I kinda forgot what colour they are, but you get the idea) . You should find some little balls on the ground, which you pick up. They will give mostly black pearls and sometimes mutagel.
If you’re on ragnarok, go to the sunken ship with a spino that has a couple points into weight and damage , then farm the eurypterids that spawn there for insane black pearls. Since they spawn so often, you can keep going there are get way more black pearls that you’ll need
So apparantly corrupted creatures give black pearls, anglergel and stuff luke that when they die, i found this out while on ark, (had super high drop rates so on officail its probly super rare) also corrupt rexes drop the most i find.