10 Surprising Facts About Aquarium Fish You Probably Didn't Know
, by Michael van Wassem, 4 min reading time
Does your goldfish really only remember for three seconds? Discover 10 surprising facts about aquarium fish and what they mean for their care.
Aquarium fish may look like quiet residents of their glass world, but far more happens underwater than you see at first glance. They feel vibrations we don't notice, sometimes breathe air and see colours that are invisible to us. Here are 10 facts about aquarium fish you probably didn't know, each with what it means for their care.
1. A goldfish does not have a three-second memory
It is a persistent myth, but research shows otherwise. Fish learn, for example, at what time feeding happens and which signal goes with food, and they remember this for at least several weeks to months. So your fish really do recognise when you walk up to the tank. Fixed feeding times and calm routines therefore work well.
2. Fish "feel" their surroundings with a lateral line
Along the sides of most fish runs a row of tiny sensory cells: the lateral line. With it they detect water flow and vibrations, even in the dark or in cloudy water. This is one reason a school of fish can turn so much in sync. Tapping hard on the glass therefore feels like a real shock to them.
3. Goldfish do not have a true stomach
Goldfish and other carp relatives do not have a stomach like ours: food passes almost directly into the intestine. This means they can only process a little at a time and always seem hungry. Give a few small portions a day rather than one large one, and do not feed more than they eat in about two minutes. Suitable fish food makes portioning easier.
4. Goldfish can see ultraviolet light
Like many birds, goldfish have an extra type of colour receptor in the eye that lets them detect ultraviolet light. So they see their aquarium in colours we do not know. In practice this mainly means that daylight and aquarium lighting influence how they experience colour.
5. A betta breathes air from the water surface
Besides gills, bettas (Siamese fighting fish) have a labyrinth organ that lets them take in air. They regularly swim up briefly to "gulp" air. Make sure an air gap remains between the water and the lid, and that the air there is not ice cold.
6. Corydoras catfish partly breathe through their intestine
Corydoras catfish sometimes dart to the surface to take a gulp of air. They can absorb part of their oxygen through the intestine. Occasionally this is normal. If they do it constantly, check the water quality and oxygen level.
7. A female guppy can give birth months after mating
Guppies are livebearers: they give birth to fully developed young fish instead of laying eggs. Females can store sperm and have several broods after a single mating, sometimes months later. If you do not want unplanned offspring, choose the make-up of your group carefully and provide enough plants as hiding places.
8. Most fish have no eyelids and still sleep
Most fish cannot close their eyes. They rest with reduced activity, often near the bottom or among plants. A fixed day and night cycle with a timer on the lighting helps, and hiding places such as aquarium decoration give them rest and security.
9. Goldfish can live a very long time
With good care, goldfish often reach 10 to 20 years, and some live even longer. The best-known record is an English goldfish called Tish, said to have reached 43 years. They also grow larger than many people think and do not belong in a small bowl. A spacious aquarium with good filtration and proper water care products helps them grow old in good health.
10. The colour of your fish partly depends on what it eats
Red, orange and yellow shades come partly from pigments (carotenoids) in food, because many fish cannot make these themselves. With varied, good-quality food, colours stay more vivid. Stress or poor water quality can make colours fade, so a fish that suddenly turns paler is a reason to check your water values.
Summary
Fish learn and remember, feel vibrations through their lateral line, some breathe air, and many goldfish live longer than you would think. For you as a keeper, it comes down to fixed routines, small portions of food, good water quality and plenty of hiding places.
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