They swim differently than humans do. They breathe under water. And most of them neglect their young ones.
I’m talking about fish.
Just like people, fish come in all shapes and sizes. While some may think fish appear flat, a few species can actually become wide or long and shape shift to deflect predators. For instance, the porcupine fish can be both flat and round: when deflated, it is flat, but when it feels threatened, it swallows water and inflates to two or three times its normal size.
The porcupine fish will never be as large as the whale shark, however, which grows up to 45 feet long. Smaller fish who are unable to use their size to scare away predators often use their colors or swim in groups to confuse their enemies, instead.
Unlike humans, fish swim all of the time. They swim more fluidly through water by twisting their backbone, whipping their heads to the side, and flipping their tails. Humans swim differently than fish do, and primarily stay above the water's surface by moving their arms and legs.
All living things—including fish—need to breathe oxygen. People breathe through their mouths and noses. However, fish get their air another way: through their gills, which are on the side of their bodies. Gills filter oxygen so that fish can breathe under water.
Humans and fish also have a number of key differences when it comes to reproduction. Humans either keep their babies and raise them or give them up for adoption, while fish leave their eggs dispersed and swim on without them. Very few fish stay with their offspring to protect them.
Fish are an unequaled species on Earth. They have needs like humans do, but they meet them in different ways.
[Source: Amazing Animal Facts]