By Neale Monks, Ph.D.
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Floating fish food by Tony Terceira.
Sinking fish food by Tony Terceira.
Fish feed in a variety of different ways, so how you feed your fish will depend upon what species are being maintained.
Small community fish like tetras and livebearers should be fed once or twice per day, and need only as much food per meal as the fish can consume within a minute or so. There should never be any leftover food. Use floating fish food for surface-feeding fish and sinking fish food for species that stay close to the aquarium’s substrate.
When feeding your fish, inspect your livestock. Start by counting the fish to make sure they are all present. Check the fish for signs of damage or disease. Often the first sign of problems with fish health or aquarium water quality is odd behavior, particularly at feeding time. So, if one or more of your fish isn’t interested in its food, investigate further.
Properly fed aquarium fish should have gently rounded abdomens. Overfed fish have a bloated look and will often be lethargic. Chronically underfed fish will look emaciated, in many cases with a distinctively concave ventral profile.
Saltwater fish can be divided into four basic sorts, as far as feeding goes: bold feeders, plankton-eaters, herbivorous grazers and micropredators. Bold feeders are those saltwater fish such as damselfish that greedily swim into the open at feeding time. Feeding these fish one or two modest meals per day works well.
Plankton feeders can be trickier to feed, the key thing being that they need multiple small meals per day to do well. Anthias are the classic example of plankton-feeding fish, and because they need several meals per day, they easily starve in captivity.
Herbivorous grazers are often bold feeders, as well, but in addition to flake or frozen food, they also need green foods. Surgeonfish and saltwater angelfish are classic herbivores. They need constant access to live algae or some suitable substitute, such as nori.
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Micropredators, such as this Mandarinfish, consume small animals.
Photo by Tony Terceira
Micropredators are things like seahorses and Mandarinfish that consume small animals of various types. In mature, very large aquariums, they may be able to find sufficient numbers of copepods and other small crustaceans to do well, but relying on this has lead to the demise of countless fish. Instead, the aquarist will need to provide live or frozen alternatives at least once per day. Because of their particular needs and often rather slow feeding habits, micropredators should not be mixed with community species.
While some invertebrates will find their own food in reef aquariums, algae-eating snails for example, others need the aquarist to supply food.
Feeding nocturnal fish can be difficult because the aquarist cannot always tell if one particular fish is eating the food put out for it. This is especially the case with nocturnal predators like spiny eels and mormyrids. When maintaining these slow-feeding species, do not mix them with anything that might eat their food, such as catfish or loaches. Feed nocturnal predators around five times per week.
Large Predatory Fish
Most fish are predators, of course, but large predators fall into their own category for several reasons. First, they do not need to eat every single day. Indeed, really big predators, such as large catfish and piranhas, may only need to be fed a couple of times per week.
Second, these fish have a tendency to gorge themselves in the wild, eating one big prey item and then not eating anything else for several days afterward. It is debatable whether this is a sensible approach in the aquarium because the resulting spike in ammonia after a massive meal can cause major problems, in terms of water quality. Some predators are also prone to regurgitating undigested food if they’ve consumed too much, making things even worse. The safest approach is to offer small meals several times a week, perhaps even every day. As ever, the goal is to maintain a gently rounded rather than swollen abdomen.
Finally, there’s some anecdotal evidence that the use of live rather than dead prey makes predatory fish more aggressive. As discussed last time, feeder fish should be avoided.
Herbivores do best when given constant access to suitable green foods. Because plant material is low in protein, it has little impact on water quality.
Without exception, juvenile fish (fish under three months of age) do best when given several small meals throughout the day. In the case of very young fish (under 1 month of age), as many as six meals per day is recommended. Some of those meals can be algae that you have thoughtfully allowed to grow in the aquarium.
Feeding Fish During Vacations
For periods of up to seven days, you can easily leave a mature aquarium unfed. For longer periods, you have several options. Big fish, particularly predators, can easily go two weeks or more without food if they are healthy. Herbivores like goldfish can be given a bunch of cheap aquarium plants, such as pondweed, and left to their own devices. Community aquariums can usually be catered for using automated feeders. Reducing the rations is a good idea, of course, because you won’t be around to remove waste or perform water changes.
Asking friends to feed your fish isn’t recommended. If you must do this, divide the food into portions before you go, and hide the rest. Leave only enough for one meal every three to four days.
Neale Monks studied zoology at the University of Aberdeen in the north of Scotland and obtained his Ph.D. at the Natural History Museum in London. He's also been a marine biologist, a high school teacher, a university professor and a museum's exhibit designer. But his real love has always been tropical fish. His particular interest in brackish water fish culminated in his editing of the first encyclopaedic book on the topic, 'Brackish-Water Fishes', published by TFH in 2007. Neale regularly contributes to all the major English-language fishkeeping magazines, focusing especially on community tanks, biotopes, healthcare and water chemistry issues. After living in London and then for a while in Lincoln, Nebraska, Neale now lives in a quaint cottage in a pretty market town in Hertfordshire, England, where he divides his time between teaching and writing.