Big fish are like the boss fish in the ocean or lakes. They are the largest and strongest fish that swim around in the water. They can sometimes be hard to catch because they are really good at swimming away from fishermen or hiding in the water.
It's like when you play a game and the boss is really hard to defeat because they have lots of power and abilities. The big fish are like that, too. They have big muscles and can swim really fast so they are hard to catch.
Some big fish, like sharks, have really sharp teeth and can eat other fish. But not all big fish are mean. Some, like whales, eat tiny animals in the water instead.
People like to catch big fish because it's a really fun and exciting challenge. But we also have to take care of them because they are important for the balance of the underwater world. Plus, they're pretty cool to look at and learn about!