What happens to a goldfish that is left in the dark?

Goldfish, like many other animals, have an internal clock or circadian rhythm, which is based on a 24-hour cycle and helps them regulate their activity and other physiological processes. These processes are heavily influenced by light.

If a goldfish is kept in complete darkness for an extended period (several days or more), its circadian rhythm can become disrupted. This disturbance can cause several effects on the goldfish:

Impaired activity patterns: Goldfish may lose their normal pattern of activity and rest, becoming less active during the day and more active at night, or showing irregular patterns of sleep and wakefulness.

Feeding issues: The disruption of the circadian rhythm can affect the goldfish's feeding habits. It may start to lose its appetite or eat at irregular times.

Breeding disruptions: In goldfish bred for reproduction, constant darkness can interfere with their breeding behavior and reduce the chances of successful spawning.

Health problems: Long-term lack of light can also result in a weakened immune system, making the goldfish more susceptible to illnesses and diseases.

It's important to note that goldfish still need a natural day/night cycle, even if they are kept indoors. Providing adequate lighting with periods of light and darkness helps regulate their biorhythms and overall well-being.