In Jellyfish Hunter, it's hinted that there are about 4 million jellyfish. SpongeBob and the other jellyfishers have caught 3,999,999 (and let them go), but could not catch one jellyfish they named No Name. When the Jellyfish Race in the Fields was running low, the sign that says Jellyfish Fields now crossed off the word million making the sign look like: Jellyfish Population: 4 when the original sign was Jellyfish Fields: Pop. 4 Million. The 1st main appearance of the entire Jellyfish population was in the episode Jellyfish Hunter.