Too much food can make a fish sick. It isn’t that the creatures eat themselves to death. What they actually do is drown in their leftovers.
Your fish may spend its entire life in 10 or 20 gallons of water, so the quality of that water dictates, to a large degree, whether – and for how long – they will survive. Overfeed them, and their uneaten food and/or excessive nitrogenous waste production can literally poison them to death.
How Much is Too Much
As a general rule, your fish should be fed no more than what they can eat in three minutes; in most cases, a single daily feeding is adequate. There are exceptions to this guideline, especially when you consider very young fish (fry), which usually need to be fed several times a day.
If you want to get technical, researchers have a come up with a way to calculate how much food each fish requires. Tropical ornamental fish (small cichlids, for example, or moonlight gouramis, neon tetras or zebra danios) generally must consume between 1.0 and 2.5 percent of their body weight in food each day. Thus, an aquarium with 20 neon tetras (0.2 g/fish), 10 leopard danios (0.4 g/fish) and two moonlight gouramis (6.0 g/fish) would contain 20 grams of fish with an estimated daily feed requirement of between 200 and 500 milligrams (approx. 1/50th of an ounce).
The easiest way to kill a fish by overfeeding is to introduce the “good neighbor syndrome.” The scenario is all too common: You’re going away on vacation and ask a neighbor to take care of the aquarium. Eager to keep the fish happy, they put too much food in the aquarium, thus developing a negative feedback loop: Ammonia levels rise, the fish turn anorexic, the neighbor gets nervous, more food goes into the tank. The fish suffer.
How do you avoid the problem? Feed the fish well a day or two before you leave and let them fend for themselves until you return. Most aquarium and pond fish can easily survive seven to 10 days without supplemental food (natural foods, such as insect larvae, algae and zooplankton are frequently available).
When the Meal’s Too Big
If there’s too much food in the tank, the remedy is quite simple. You can use a fine net to “scoop out” uneaten flakes and pellets; a siphon hose will vacuum up smaller particles. If the fish don’t seem to want to eat, change 25 percent of the water once a day for at least four days. If overfeeding becomes a chronic problem, you can install an automatic feeder (available at most pet stores), which will provide a steady, consistent food supply.