Goldfish are not orange guppies with a three-second memory.
While goldfish are often heralded for having short memories and small brains, they are surprisingly smart. They can be trained, and studies have shown they can retain lessons for up to three months.
Additionally, they come in all colors, sizes, and shapes. If you take really good care of them, they can even be your companion for half a human lifetime.
Goldfish can breed with koi, but the offspring will be sterile. (Like a horse and donkey making a mule.) If you are breeding goldfish, remove the eggs when they are laid or the parents will eat them!
Goldfish can live in colder temperatures than most other aquarium fish but prefer their water at 50 to 76 degrees Fahrenheit. They are omnivores so feed them plants and insects, maybe even small fish.
The average life span is six to eight years but they can live up to 40 years old!
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Goldfish size can be restricted by tank size and poor water quality. They can actually grow to one foot and seven pounds!
During breeding season, sex can be differentiated. Males get spots on their gills whereas a female's belly swells. The shape of a vent near the anal fin also distinguishes males from females.
The shape of a goldfish varies among species. Some have bulging eyes and flowing tails.
They can see color better than humans! For this reason, they should not be kept in a dark room.
An individual's scale coloration can change in night and day. The scales are brightest in natural light.
Not all goldfish are orange. They can also be gray, white, black or olive green including a mixture of colors and spotted patterns as well.