If someone is described as a big fish in a small pond, they are very important or have a lot of influence but only in a small area or group.
Paul is a manager of a small company; he likes to be a big fish in a small pond.
Jane might think she has power but she's just a big fish in a small pond.
If someone is described as a cold fish, it means that are unfriendly and don't show their emotions.
Julie's a cold fish; she never speaks to anyone in the office.
Whale sharks are the world's largest fish; the longest ever recorded was over 13 metres. They are harmless filter feeders that suck in plankton and small fish. These distinctively yellow-spotted sharks are found throughout the world's oceans, preferring the warm and tropical waters around the equator.