How long can goldfish go without food?

In an emergency scenario, you may need to let your goldfish go without food. This is not the same as fasting, which should never be attempted without veterinary supervision, and is not an excuse for vacation care. But, when the situation occurs, how long can goldfish go without food?

Temperature Considerations

Remember that almost all pet fish are ectothermic, meaning, their body temperature is almost the same as their water temperature. When the water is warmer, their metabolism will burn faster, their immune function is optimal and they are getting ready to make more baby fishes. Goldfish, not being tropical fish, do well in a wide temperature range between 60-80F (15-27C). At the colder end of this spectrum, their metabolism will be much slower than at the higher end. Depending on the emergency situation you currently face, your tank temperature may be at the higher or lower end. If you can, try to bring down your water temperature, very slowly. This will decrease your fish’s metabolism and decrease their energy demands. As long as the water is not frozen, your fish will be okay.

Here are some tips to decrease your water temperature:

• Move your tank to a lower floor of your home, preferably your basement. Don’t forget the light!
• Add ice to your tank in small amounts. Don’t forget to add water conditioner! Frozen water bottles can be reused.
• In outdoor ponds, add shade structures such as umbrellas, plants or tarps at least 1′ off the surface with side ventilation.
• Have your aeration pull colder air if you are able to put it in the flow from an air conditioner.

If you are in an emergency situation where your tank is getting too cold, check out this list of tips.

What is your goldfish eating?

Your goldfish’s diet directly impacts your water chemistry. If you are not able to feed your fish, I doubt you’re able to keep up with your regular maintenance. In order to decrease the ammonia output from your fish, select a diet that has lower dietary protein. Most goldfish should be eating around 30% protein regardless of their situation unless they are show fish. Again, the colder your fish’s tank, the lower their metabolic demands, so less food or fewer feedings will help them out.

Goldfish Body Condition

Unlike cats and dogs, fish body condition can be hard to assess. Body condition is a visual evaluation of a fish’s fitness vs. obesity vs. emaciation. Given the variety of goldfish body types, it is very hard to compare various breeds. But, a better body condition, with adequate muscle and fat storage, will be able to withstand temporary periods of non-feeding better than emaciated fish.

So, how long can goldfish go without food?

The answer to this question comes down to your tank or pond temperature, how well you can maintain it, and your fish’s weight and body condition prior to stopping food:

These are general guidelines only! They are not prescribed fasting intervals. Only withhold food in an emergency situation or under an aquatic veterinarian’s direct orders.

Conclusion

In summary, you should never withhold food from your goldfish unless in an emergency or under direction from an aquatic veterinarian. Withholding food because the “internet told you too” is not beneficial to species that require energy to constantly swim.

References

Clarke A, Fraser KPP. Why does metabolism scale with temperature? Functional Ecology. 2004;18(2):243-251.

Clarke A, Johnston NM. Scaling of metabolic rate with body mass and temperature in teleost fish. Journal of Animal Ecology. 1999;68(5):893-905.

van den Thillart G, Smit H. Carbohydrate metabolism of goldfish (Carassius auratus L.). J Comp Physiol B. 1984;154(5):477-486.