They need blue coin doors as well, or a special magic for them, or just some sort of use for them, as of now all I see them as is compensation if you fail on a minigame.
I found a glitch! If you get the MK II Booster, with max fuel and a chainsaw(heavy weights help) you can use the booster to get below 300. The booster is faster than the pull up. I managed to get the Glowing Shrimp and the Giant Plankton, but you also need a lantern. And the Bored Gamer fish runs away.