Inappropriate Feeding—Not Just Overfeeding—Kills Marine Fish

“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.