Scientists created the first-ever peanut butter jellyfish by blending all-natural creamy peanut butter with saltwater and adding it to the tanks of moon jellies. Aquarists at the Dallas. Goofy as the experiment was, peanut butter is a potential source of protein for jellies, fish and other aquarium residents. Worry not for the experimental jellies: They scarfed the peanut-butter protein out of their tanks and actually grew about 0.2 inches (4 millimeters) in 8 days. They also took on a brownish hue.