What is how big are fish brains?

The size of fish brains varies depending on the species and their lifestyle. The brain of a small fish, such as a goldfish, can be as small as the tip of your finger. Meanwhile, some species of tuna have brains that can weigh up to approximately 4.5% of their total body weight, making them some of the largest brains in the fish world. Despite their small size, fish brains are still incredibly complex and have evolved to help them sense their environment, hunt, and avoid predators.