Salty Q&A: How Often Should Your Fish Fast?

For a zooplanktivore such as Anthias, who are frequent feeders, withholding food isn't necessarily advantageous

For a zooplanktivore such as Anthias, who are frequent feeders, withholding food isn’t necessarily advantageous


I’ve been told that it’s a good idea to avoid feeding aquarium fish on occasion, for example once every week or once every other week. I guess this stands to reason because fish in nature can’t always get a meal. Do you agree with this, and if so, how frequently do you recommend doing it?” – Submitted by Candace Brown


While I don’t have an issue with the practice of occasionally fasting fish, I’m always wary of making any sort of blanket recommendation such as “Marine fish should be fasted every X number of days.” In my opinion, a much better approach is to think in terms of feeding in a manner appropriate to the particular species—which may or may not include fasting.

For instance, some predatory species, such as groupers and moray eels, naturally take in large prey items in one sitting and then go without eating for a relatively long interval until another prey item happens along. With these fish, it may be appropriate to feed only once or a few times per week and then allow them to fast in between meals.

On the other hand, zooplanktivores and herbivores (such as anthias and many of the tangs/surgeonfishes respectively) naturally feed frequently, if not continuously, throughout the day. Thus, in an aquarium setting, it’s appropriate to provide multiple small feedings each day for zooplanktivores and continuous grazing opportunities for herbivores. In my opinion, it’s not necessarily advantageous to fast these types of fish on a routine basis, so I’ve never made a habit of doing so.

That being said, there are times when it can be beneficial to withhold meals from your fish whatever their natural feeding proclivities may be. For example, if you’re going to be out of town over the weekend and you’re concerned an aquarium sitter will overfeed your fish, consequently ruining your water quality, you can simply avoid feeding them while you’re gone. Most adult fish can easily go several days without eating with no ill consequences. Another instance in which it can be advantageous to fast a fish is when you’re transporting it in a shipping bag. By withholding food for a day or so ahead of time, the specimen will be less likely to foul the shipping water with its own waste.

Of course, these are just a few examples of when fasting is recommended. Fellow salties, if you can think of others to contribute, please feel free to do so in the comment section below.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. I would never withhold food from fish unless like said, groupers, moray eels or Great White sharks which can get along on one or two accountants a year. All other fish eat constantly and also should in a tank. We sometimes fail to realize that we are not fish. Fish do not get fat. Most fish have no “fat”. They have oil instead. We can use our fat reserves because we are warm blooded and our fat can circulate through our system. Some of us can live for months on our fat. (no one here I am sure)
    Cold blooded fish can make energy from their oil but they can’t store much as most of it is in their liver and that is only so large. Fish don’t get love handles or pot bellies for a reason. Fish also don’t have to exercise as sedentary fish seem to be as lean as energetic fish.
    When, and if, we exercise some of our solid fat will liquefy because we are hot, some of us, such as Angelina Jolie are hotter. (so to speak) And we use that for fuel. Of course we also have a flaw in our physiology which is our solid fat also gets built up in our arteries. Fish don’t have that problem because all they have is oil.
    So feed your fish every day or twice a day unless you are going on vacation, then they can eat cake.

  2. Dave Davis says

    I don’t know if this counts but I was advised by a LFS owner once when I bought a File Fish for the purpose of eating aiptasia that if I held off feeding the tank for a few days that would help force the File Fish and Peppermint Shrimp to consume the aiptasia. She had anecdotal evidence from another customer that with-holding food for three days had worked in the customers tank. So far I’ve been reluctant to try it as I’m not one to deprive an animal in my care of food.., it just seems inhumane. After all my name is not Mother Nature, that’s her job to be heartless and cruel.

    • Jeff Kurtz says

      Hi Dave! That technique can be successful and might be worth a try with your filefish. I wouldn’t worry about withholding food for just a few days. Fish can generally shrug off a handful of days sans feeding with no difficulties. Besides, it will have food available in the form of those pesky Aiptasia!

  3. Tiffany Cannon says

    We don’t withhold food but have cut back to only feeding once per day now that all our fish have grown out of their juvenile phases. We’ve also been told that some of our fish should be fasting but this hasn’t seemed feasible. We have a tank with a mixed bunch of fish. The highly energetic tangs certainly need feeding at least once per day. But we also have a miniatus grouper and snowflake eel. I have found that I can essentially fast the group and eel by not feeding predator sized food every day. The grouper won’t bother eating if I only serve frozen cubes and the eel can’t see well enough to find it before the fish have eaten everything of substance. Every few days we cut up squid, shrimp or fish and feed the big boys.

  4. I have 3 different wrasses, 2 tangs, and a magnificent fox face; I feed them 3 – 5 small meals per day. These types of fish are constantly hunting for food and algae. Our reefs typically become barren of these foods in a short time so I feel it is important to feed my fish regularly and also for their enjoyment. They are stuck in a glass box for our enjoyment so the best I can do is keep them well fed and aquascape my reef with plenty of caves and hiding areas to keep it interesting for them. They love it when I add new coral colonies for them to inspect.

  5. I would never withhold food from fish. I have bought a new automatic fish feeder machine, it works brilliantly when we are not at a home or traveling to some short trip. So, my fish never often fasting. The timer of the fish feeder is fixed when they need they have it.

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