Goldfish are native to East Asia and are related to the carp family. In their natural habitat, goldfish eat insects, plant matter, and crustaceans. They basically feel like their stomach is a bottomless pit and can eat themselves to death. Their intestines eventually get blocked due to their overeating and they die.
The overeating also causes them to create more feces, because their body can’t digest the protein quickly enough. Goldfish can be conditioned to their environment and their behavior can be conditioned by their owners. They have social learning skills and associative learning abilities. Their acute vision allows them to differentiate humans.
They tend to act differently with their owners than with other people. For example, they will swim around their tank quickly, swim to the front of the tank, or swim to the surface when their owner is near. Upon seeing other people, goldfish will swim away and hide. After time goes by, they learn to associate their owner with food and will begin to beg for food.