I’m sure you’ve heard of some people being described as “swimming like a fish.” It might surprise you to learn that some fish don’t swim well at all.
Why would some fish be poor swimmers? The simple answer is they don’t need to swim well.
For example, if the pufferfish (also called blowfish) is chased, it doesn’t have to swim fast to escape. It simply swallows a lot of water and inflates to be so large, and in some cases so spiky, that it can’t be eaten. Pufferfish are also toxic with no known antidote.
Blob sculpins (also called blobfish or fathead sculpins) live as deep as 4,000 feet off the Australian coast. They don’t have any muscle mass, which makes them less dense than the depths they live in, which is why they are able to survive deep-sea pressures. They simply lie still and eat whatever happens by on the seafloor.
Seahorses are always fun to watch, but their unique bodies make them some of the slowest swimmers in the ocean. They make up for it by being incredibly fast predators, as long as the waters around them are still. They eat copepods, tiny crustaceans that can flee in as little as two milliseconds. But a seahorse can strike in one millisecond.
So you don’t have to swim well to survive in the ocean. That is, as long as your energy can be used for other successful survival mechanisms.
For more detail, see “Why Some Fish Are Really Bad At Swimming” by Liz Langley (https://www.nationalgeographic.com/animals/article/fish-behavior-swimming-blobfish-seahorse-news?).