A fish's ability to survive without food is influenced by a variety of factors, including the species of the fish, its age, size, overall health, water temperature, and whether it is in a state of hibernation in the wild or living in an aquarium.
Many healthy fish can survive for 1-2 weeks without feeding in a well-maintained aquarium. Some hardy species may be able to endure slightly longer periods without food - up to three weeks in some cases - but this generally is not recommended as it could weaken their immune system and make them more susceptible to diseases.
Especially for pet fish in an aquarium, the duration without food might be extended because of the prevailing conditions in the tank. The fish might nibble on algae, plants, or microscopic creatures in the water, which can provide them with minimal nutrition. However, fish owners should keep in mind that certain species of fish are predaceous and might start eating smaller fish in the tank if regular feeding is not maintained.
The water temperature of the tank or environment the fish is in also plays a significant role. Fish metabolism is usually slower in colder temperatures. Thus, a drop in water temperature can cause some species of fish to require less food. For instance, koi fish hibernate during the winter and can survive for months without food.
Age and size also play a role. Mature fish can usually survive without food longer than younger fish. Newborn fish or fry require constant feeding and may likely perish if not fed regularly. Similarly, smaller species of fish tend to have a faster metabolism comparing to larger ones and may not survive long periods without feeding.
For fishes in the wild, facing periods of food scarcity can be a natural occurrence, particularly during colder months. They can adjust their metabolic rate to become more energy-efficient. Furthermore, many species can survive by eating less-preferred food types or by foraging or hunting less frequently.
While it's critical to remember these factors, it's just as important, if not more so, to remember the potential risks and harmful effects of not feeding your fish. Extended periods without food can result in weakened immune systems, slowed growth, and increased susceptibility to diseases. It's possible that the fish will survive, but at the cost of their overall health and well-being.
In summary, while most fish can survive without food for 1-2 weeks, it is not recommended. The health of the fish, the type of fish, the conditions of the tank, and the availability of other food sources (natural flora or smaller fishes) can all factor into how long a fish can go without being fed. Fish owners should ensure their fish are fed regularly to maintain the fish's health and ensure a well-balanced environment.