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

Question

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

Answer

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.