Ten Misconceptions and Fallacies about Fish Keeping

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Updated: March 5, 2006

Here are ten misconceptions that I frequently encounter. The explanations of why these ideas are misconceptions should add enjoyment and success to keeping fish in aquariums.

  1. "Keeping fish is hard work!"

    It needn't be. You do have to obey a few simple rules:

    • Never put soap, hand lotions or paints anywhere near an aquarium
    • Anything you use in or with your aquarium such as buckets and cleaning accessories should be used ONLY for the aquarium and not for washing the car, mixing cement, etc.
    • You need to supply clean, well-oxygenated water of the right temperature and possibly of particular chemical composition (saltiness, pH) depending on the species you choose to keep
    • You must be prepared to do some weekly or at worst bi-weekly maintenance besides feeding your fish. Feeding can typically be done daily.

    There are many, many species of fish that can be successfully kept and even bred with a minimum of effort, where weekly maintenance consists of removing an inch or two of water and replacing it with fresh-water. There are also numerous species which have much more specialized conditions and should you wish to keep those species, you must be prepared to meet their requirements.

  2. "I'll start with a small tank, and if I like it, I'll get a larger one later."

    This seems to make sense but in fact is probably the principle reason why people give up on keeping fish. Why? Because, a 10 gallon tank is much harder to maintain than a 20 gallon tank. The reason is simple: there is so little space and water in a 10 gallon tank that if anything goes wrong, there is no buffer.

    This applies in particular to water quality: a little uneaten food can quickly foul the water in a small tank, whereas it would have no effect in a larger tank. Larger tanks require less frequent maintenance and are much more "self-sustaining" than small tanks.

    Small tanks also cause difficulty when people try to put too many fish in too small a space, or when one of the fish in a small tank becomes aggressive: there is no place to hide in a 10 gallon tank.

    There are some species of fish that do quite well in a 10 gallon tank, but many do not. Ten gallon tanks are also very useful for specific tasks like raising fry, and breeding certain species of fishes, but unless you have a specific reason for wanting a 10 gallon tank, I highly recommend you start with at least a 20 gallon tank.

    The difference in cost between a 10 gallon setup and a 20 gallon setup is barely noticeable in the long run. You can use, and in fact need, all the same equipment to run both sizes of tank, so you might as well get the larger tank and enjoy it. In fact, if you can, start with a 30, 40 or 50 gallon tank and you will be much happier in the long run.

  3. "One type of filter is better than another."

    Each of the many kinds of filtration has its pros and cons. Some are more suitable for some kinds of aquariums, others are more suitable for other setups. For example, a sponge filter is great for a small aquarium in which you breed cichlids. It keeps the water clear, it won't suck up babies, it is easy to maintain, it is relatively inexpensive and it lasts for years. However, it may be less suitable in a tank with larger fish for the simple reason that the large fish may chew it to pieces. I have one large pike cichlid who regularly tears apart sponge filters. Also, you may not like the look of a sponge filter sitting inside a tank. Similarly, each of the other kinds of filtration has pros and cons so investigate carefully what kind of tank you want (e.g. ,Central American cichlids; South American catfish; South East Asian community tank, etc) before deciding on a filtration system.

  4. "You need to buy all sorts of chemicals to add to the water."

    I use chemical additives very sparingly. Some types of aquarium setups require specific chemicals (for example, East African cichlids require hard alkaline water), but be careful and educated in their use. Dumping in a bunch of medicines or water treatments may not solve problems, but in fact may create new problems.

    Similarly, the role of charcoal is highly debatable. Water quality is maintained by your filtration system (whatever it may be) by two basic means: mechanical filtration and biological filtration. Mechanical filtration means getting the big chunks of stuff out. Biological filtration refers to the actions of tiny bacteria that break down fish waste and uneaten food into harmless by-products. The best way to promote biological filtration is to provide lots of surface area for the bacteria to grow, which is why sponge filters, trickle filters and wet-dry filters all work so well. These bacteria need a flow of well-oxygenated water to do their work and each of these filtration types attempts to create those conditions.

    We used to think that charcoal in itself removed toxins from the water, and in fact it does. What is debateable, however, is how long it continues to do so after being put in the filter. Exact numbers depend on many, many factors but it may be a matter of days or even less. The charcoal does provide lots of surfaces for the growth of bacteria and this is probably charcoal's primary usefulness; however, we now have better alternatives for that function. The bottom line: I never use charcoal and haven't for years. It is messy, expensive, and in my opinion of negligible help in maintaining water quality.

  5. "I can't afford a heater right now, so I'll start without one"

    Don't do this. If you are keeping tropical fish, you need an electric aquarium heater, unless you are prepared to keep your room temperature above 80oF all the time (which is what people who keep a large number of tanks do). Tropical fish come from warm water that does not get cold. Cold water kills them. Sometimes they die right away, but more likely they become much more susceptible to infections and other illnesses.

    Similarly, all heaters are not created equally. Is the most expensive heater necessarily the best? Not necessarily, but a very cheap heater is probably exactly that: a very cheap heater. It may work most of the time, but it may also "stick" meaning it stays on and in a matter of hours cooks your fish. Personally, I use Ebo-Jager heaters in my tanks and have done so for almost 15 years. They last for many years and are well-worth the investment.

  6. "I know this species gets large, but I'll just keep it for awhile and then trade it in or give it to a public aquarium"

    This is irresponsible. If you cannot keep a fish when it reaches adult size, do not get it in the first place. The person selling you the fish should warn you if you are buying something that "gets big". Common fishes that fall into this category are red tail catfish, arowanas, some pike cichlids, pacus (relatives of the piranha), snakeheads, lionfish and certain plecostomus catfish.

    Red tail catfish grow to several feet in length as do arowanas, pacus and snakeheads. In addition, many fish grow much faster than you might think. An oscar can reach adult size of over a foot in under a year.

    You must also consider the quantity of food that a large fish eats. An adult lionfish (a beautiful marine species of fish) can easily consume dozens of goldfish a week. This can really add up in cost. Many people buy baby Wolf cichlids (Parachromis dovii). The wolf cichlid is a large predatory Central American cichlid. They are a fascinating fish, but adult males are 2 feet in length and eat a lot.

    Finally, public aquariums are inundated with overgrown red-tail catfish and snakeheads and they don't want more, nor are they obligated to take them from you. Nor for that matter is the pet store where you bought the fish when it was small. They may do so, and I applaud stores that do this, but understand that they are doing you a real favor.

  7. "If I keep a fish in a small tank, it won't grow large."

    There is a tiny bit of truth to this. When fish live in a confined body of water like an aquarium, the waste products which they produce tend to stunt or slow their growth. So, yes, a fish will not grow as fast in a small aquarium as it will in a large aquarium. However, unless the fish becomes extremely stunted it will eventually outgrow a small tank if it is normally a large species. Some fishes, snakeheads in particular, are more immune than others to the growth suppression effects of a small tank, and grow large, quickly, in spite of being kept in small tanks. Snakeheads can quickly reach two or more feet in length and will grow so large that they cannot even turn around in their tank.

  8. "When my fish gets large, I'll release it into a local river or lake"

    Do not do this under any circumstances! The introduction of exotic fishes into local waters can cause all sorts of problems for native fishes, and is highly illegal. You are not helping your fish either. If it is a tropical species, it will die when the water gets cold. In the meantime it will compete against naturally occurring species for food, space, etc, harming local populations. Aquarium fishes may also introduce diseases to local fishes.

    The release of aquarium fishes is the number one problem created by the aquarium hobby and is the reason why many species are banned in certain States/Provinces, i.e., because their release would likely have serious consequences. This is a real shame because some of the banned fishes, e.g., freshwater stingrays are banned in California, are interesting animals that serious aquarists would love to keep.

    Once again, the actions of a few irresponsible people are harming many others, intended or not.

  9. "Large fish eat live food."

    Not necessarily. Too often people assume that just because a fish is large it must be fed live food. The best example I know of is the tendency for people to feed live goldfish to Red Devils, a common Central American cichlid. This doesn't hurt the red devils but it certainly isn't necessary. Red devils do quite fine on trout chow pellets.

    Other large fish are definitely piscivorous (meaning they eat only other fish) and should be fed appropriately. The bottom line here is that the size of a fish does not tell you a whole lot about what it eats, although it does tell you something about how much it eats.

  10. "Species x can/cannot be kept with species y"

    The assumption here is that all individuals of a given species behave in exactly the same way all the time. This is absolutely not true (and in fact what I study for a living, so I'm not just making this up).

    Yes you can make some predictions about the likelihood of certain species getting along. For example, if you put a neon tetra (a tiny South American schooling fish) in with a Jack Dempsey (a species of Central American cichlid of moderate size), odds are the neon is going to be lunch for the Jack Dempsey. But just because a fish is named "Jack Dempsey" doesn't mean that it is going to fight every other fish it encounters, all the time.

    Behavior of fishes, and of cichlids in particular, is highly dependent on context. For cichlids, breeding status explains a lot of what we see. Cichlids are excellent parents, and that means keeping all potential predators away from the nesting area and babies. Any fish that remains nearby must be driven away or killed. In the confines of an aquarium, where the former is not possible, the latter is the typical result. Cichlids are particularly prone to being aggressive most of the time because they are prone to being reproductive, either actively caring for kids, or trying to obtain a mate to breed, most of the time.

    It is often a good idea to keep fishes from similar parts of the world together and not to mix fishes from different parts of the world. Fishes from the same part of the world typically require the same water conditions. This does not mean that you are safe to put two species together just because they come from the same locality: you should also consider the diet of each of the species to ensure that it does not include one of the other species!

In sum, examining and thinking about each of these ten misconceptions should help you to be a better aquarist.


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