Inappropriate Feeding—Not Just Overfeeding—Kills Marine Fish

Everyone knows it's feeding time in the aquarium!

Everyone knows it’s feeding time in the aquarium!

“We lose a lot more fish to overfeeding than we do to underfeeding.”

I’ve read or written that sentence—or some variation upon it—more times than I can recollect. While I still consider this statement to be true on balance, I think placing undue emphasis on overfeeding versus other forms of inappropriate feeding can lead to some false conclusions.

Among them:
  1. Fish have uniform needs when it comes to the volume and frequency of feedings.
  2. Good water quality takes precedence over keeping fish properly fed.
  3. Fish are secondary to corals in a reef system.
  4. Quantity/frequency of feeding is a more important consideration than the types of food offered.
  5. The risks to our fishes’ health are greater with overfeeding than with other forms of inappropriate feeding.

Let’s take these points one by one and briefly examine where they go wrong:

1) Fish have uniform needs when it comes to the volume and frequency of feedings

Nothing could be further from the truth. There’s no one-size-fits-all regimen with respect to feeding frequency and volume. For example, larger predators, such as lionfishes, typically require one heavier feeding every few days or so; zooplanktivores, such as anthias, require multiple small feedings each day; and grazers, including many tangs, need a steady supply of algae to nibble throughout the day.

2) Good water quality takes precedence over keeping fish properly fed

One of the primary reasons we place so much emphasis on overfeeding in this hobby is that doing so can cause water quality to crash very quickly. But it’s important to keep in mind that ensuring fish get enough of the proper foods to eat and maintaining good water quality aren’t mutually exclusive goals. You have to do both, and sometimes that entails stepping up water changes, protein skimming, and other forms of nutrient export to accommodate the needs of fish that are messier or more frequent feeders. (PaulB may have some thoughts to add on this subject.)

3) Fish are secondary to corals in a reef system

This point builds on the previous one. Because exceptional water quality is essential to success with sessile invertebrates, especially the more demanding SPS corals, it’s tempting to underfeed piscine tank inhabitants in order to minimize the level of dissolved pollutants in a reef tank. But fish kept in reef systems have the same nutritional needs as those kept in fish-only tanks. We can’t shortchange our fish nutritionally for the sake of keeping our corals healthy. It’s better to limit the number and size of the fish in our reefs than to underfeed the ones we have.

4) Quantity/frequency of feeding is a more important consideration than the types of food offered

Placing too much emphasis on the quantity/frequency of food offered to fish downplays the importance of offering the right types of foods based on each species’ individualized needs. It then becomes all too easy to think, “My queen angelfish gets plenty to eat. I feed it krill three times a day.” Never mind that a regular diet of krill would be terrible for this fish even if the frequency of feeding is appropriate for the species.

5) The risks to our fishes’ health are greater with overfeeding than with other forms of inappropriate feeding

Overfeeding fish is most assuredly bad for their health. Just ask any lionfish afflicted with fatty liver disease. But I think we tend to underestimate how many of our fish succumb to gradual starvation or nutritional deficiencies due to underfeeding or offering nutritionally inadequate foods. Because starving/malnourished specimens can cling to life for many months—or even years in some cases—it’s easy to attribute their deaths to other causes or dismiss them as “mysterious.”

The bottom line is, we must research the dietary requirements of the specimens in our care and make every effort to provide them the proper foods in appropriate quantities. Their nutritional needs don’t change based on factors such as the size or type of system we put them in, whether or not we provide adequate nutrient export, or how much energy we have for tank maintenance.


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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. Paul Baldassano says

    Fish in the sea rarely, if ever get the chance to over eat, Unless they live under a pier and there is a McDonalds above it. They normally eat minute bits of food all day long. There is just to much competition for them to fill their bellies. But what they do normally eat is fresh fish, shrimp or plankton often just snagging a tiny bit of this food after something else takes the first bite. We don’t have time to feed fish all day long as Jeff does but he sleeps on a hammock suspended over his tank. We normally feed once a day, sometimes twice. I like to visit my tank sometime in the morning and shoot a bit of live blackworms in the tank. The fish go nuts but they all get a couple of live worms which I think of as a vitamin pill because live worms are a complete food with all the guts along with stomach bacteria that is still live, unlike it would be in frozen food. Lately I have been thinking this live gut bacteria helps keep their immune system in tune but that is just supposition and I could be completely wrong as I have been once or twice . OK quite a few times.
    But I feel that morning feeding of worms greatly increases the fishes health because they were not designed to go all day without eating. Their next meal is mostly clams, maybe mysis or part of a Happy meal. Jeff is correct water quality is important but we should not let the fish go on a diet just to preserve the water. Change the water if you must, but feed the fish “correctly”. Flakes is not a correct food but it can be sometimes be used as a supplement if we don’t have the time because we are dating a Supermodel and she wants us to drive her to the mall.

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