Fast then refeed: compensatory growth is real in fish
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
Leaving for three days with no one to feed the tank worries almost every beginner. What fish nutrition research shows, on the other hand, is that a brief fast followed by normal refeeding usually leaves no trace on growth: the fish makes up the lost ground. Our feeding guidance is gathered in the fish food section.
Compensatory growth measured across repeated cycles
Urbinati, Sarmiento and Takahashi published in 2014, in the journal Aquaculture, a study on matrinxã (Brycon amazonicus), an Amazonian fish farmed commercially, subjected to short, repeated cycles of feed deprivation followed by refeeding (see the study). Fish that went through these cycles reached, by the end of the experiment, a final weight comparable to fish fed without interruption: full compensatory growth, driven by a temporary surge in appetite and better feed efficiency once meals resumed.
This mechanism — transient hyperphagia and more efficient digestion after a restriction — is documented in several fish species, though the outcome depends heavily on how long and how severe the fast is: a brief, isolated stop is made up far more readily than a prolonged or repeated restriction over the long term, which can instead permanently slow growth.
What this means for a home aquarium
- A weekend or a few days without feeding is not a nutritional disaster for a healthy adult fish: normal feeding resumed afterwards is generally enough to close the gap.
- An automatic feeder or a holiday feeding block stays useful for convenience and to keep water quality from degrading while you're away, not because a brief fast would threaten growth — see our guide on the holiday feeding block.
- Avoid overcompensating on return: feeding one massive ration in a single sitting to "make up" for the fast is unnecessary and mainly risks polluting the water; it's better to resume the normal routine from the first meal onward.
- The rule differs for fry and juveniles, whose rapid growth tolerates interruption less well; vigilance needs to stay stricter for them.
Frequently asked questions
Does this also apply to a sick or elderly fish?
No: the study covers healthy juvenile fish. A weakened, sick or elderly fish has smaller energy reserves and copes less well with a feeding gap, even a brief one.
How long a fast stays consequence-free?
The study tests short, repeated cycles rather than a single very long fast; it does not set a universal threshold in days. It remains sensible to size an absence to the species and its age rather than generalise a single number.
Is deliberately cycling fasts a good idea?
That isn't what the study shows — it looks at tolerance to a one-off constraint, not a benefit from choosing to fast. For balanced everyday feeding, see our article on varying fish food and the risk of deficiency. Find all our guides on the fishkeeping hub.
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This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.