Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Fish keeping myths busted

Longnosed hawkfish
Longnosed hawkfish


With so many people now having the ability to 'advise' others and pass on information which only used to be available in books lots of myths have been born. These myths sometimes have the potential to be quite harmful and so here are some of the top myths exposed.

The salt myth

Adding salt to the aquarium will stop the fish getting any diseases and make them more comfortable.

There are more myths about the use of salt in the aquarium than almost anything else. Does it act as a tonic, should it be added routinely as a preventative medication or does it do more harm than good?
Going back to the days of the goldfish bowl before the Nitrogen Cycle was really understood by most fish keepers the fish kept in a bowl were probably subjected to high levels of Nitrite on a fairly regular basis. Salt does counter the toxic effect of the Nitrite and so fish which had salt added to their water generally survived longer than fish which were exposed to Nitrite and left effectively untreated.
No one really knew why but adding salt seemed to help the fish stay healthy and so began the myth that adding salt helped the fish.

Salt does have its uses and it can be relied upon for the treatment of White Spot, Hydra, Leeches, Nitrite poisoning to name but a few. But it should not be added to a fresh water aquarium for any other reason. It will place the fish under stress and it performs no useful function.

Some fish like Mollies (not guppies, swordtails or platys) are really brackish water fish even though they are sold as community fish and they DO need some salt adding if they are to be at their best.
Fresh water fish have evolved to live in fresh water and they have a different physiology from fish which have evolved in brackish or salt water if they are forced to live in conditions which don't suit them it could lead to problems and premature death.

Fish which come from soft acidic water have bodies which are designed to hold on to salts in their bodily fluids which contain more salt than the surrounding water. To achieve this their kidneys produce lots of very dilute urine so they are able to get rid of excess water and keep hold of the salt. Water is absorbed through osmosis because a weak solution will always try to dilute a strong solution. If they are placed in water which has a higher salt level than their bodies then water will leave their body through osmosis and they will effectively dehydrate. Although they can adapt and cope with a certain level of salt their bodies are being made to do something which they weren't meant to do. The more salt there is in the water the more stress the fish will be under, and if the level of salt is high enough it will cause the eventual death of the fish.

Marine fish and fish from brackish water have bodies which work in an entirely different way. Their bodies are designed to hang on to water and expel salt, in order to do this they have to drink large amounts of water and they pass very small amounts of very concentrated urine in order to keep the salt levels of their bodily fluids less than that of the surrounding water. If such a fish (like a Molly) is put in soft fresh water it could take on to much fluid and end up suffering from Dropsy like symptoms.
Fish which have lived for hundreds of thousands of years in fresh water do not need salt adding to their water.

If you need to add salt for brackish water fish then use marine salt because it contains all the buffers to raise the pH and vital trace elements but none of the other additives that salt intended for human consumption contains.

If you need salt for a treatment use salt from the pet store which is free from harmful additives and is just pure sodium chloride.

Salt meant for human consumption is safe for humans and it is safe for fish.

The fish growth myth

Fish will only grow to suit the size of tank they are kept in.

If the fish are kept in old water month after month their growth will be stunted. This has nothing to do with the size of the tank and everything to do with

  • Very high nitrates will reduce the overall health and vigour of the fish and reduce its growth rate.

  • Fish release a growth inhibiting pheromone (an hormone which acts externally) which helps prevents them from overcrowding small pools or ponds in the wild. If this is allowed to build up in the aquarium it will slow their growth.

  • Biologically important minor and trace elements need constant replenishment or they'll become exhausted. These also have an important role on the fishes overall health and vigour.
    Making regular partial water changes will keep the nitrates and other pollutants at a very low and harmless level, and trace elements will be replenished. This along with a good balanced diet will keep the fish healthy and vigorous and GROWING regardless of tank size.

The overfeeding myth

If you over feed your fish they will eat so much that their stomachs will pop and then they'll die.

Over feeding is dangerous but not for the above reason, no fish will overeat to that extent. But overfeeding will cause food to pass through the fish only partially digested which is wasteful in itself but it could also over load the biological filters causing the ammonia level to rise and that really could kill the fish.

The fishes memory myth

Fish only have a memory which lasts for four seconds.

I don't know where this one came from, but anyone who keeps fish knows that it is wrong. Fish soon learn the tell tale signs that they are about to be fed and they remember it. They will gather under the spot where they know the food is about to arrive. they also know what a net is even if they haven't seen one in months.

The livebearers hybridisation myth

Guppies, platys, swordtails and mollies will all interbreed.

Platys and swordtails are closely related enough to be able to cross breed but none of the others are. Even though guppies and mollies are both members of the same genus they cannot produce fry together.
swordtails and platys have been hybridised for many years and the many colourful fancy Swordtail hybrids are a result of such crosses.

The in the wild myths

How often do we hear the argument that "no one does that for them in the wild". Comparing fish in an aquarium to fish in their natural habitat is pointless. Fish in an aquarium are stocked at a rate several thousands of times more heavily than in the wild. The conditions are more stable. Diseases are fewer and further apart. The food is fresher and packed full of natural vitamins. For a population of fish to remain stable each pair of adults only has to produce two fry which grow to become breeding adults, in their entire life.
The list is endless, the fact is that in order to keep fish alive in an aquarium a whole rang of life support equipment and additives is needed. Comparing this to a wild situation means nothing.

The livebearers sex change myth

In the absence of any males, female livebearers can change sex.

Some female livebearers like Swordtails take on the appearance of a male once their reproductive days are coming to an end. This could be natures way of making sure that only young fertile females are courted and bred. Simply seeing the once female Swordtail develop a sword is enough to convince some people but imagine this scenario -
There is a community tank of various small fish, among those fish are 4 female swordtails and no males, in fact there has never been a male in the tank at all, then one day the tanks owner notices that one of the female Swordtails is developing a sword and over a few weeks the transition takes place until a full sword is developed.
Then a few weeks later one of the unchanged females produces a brood of fry, this to most novice fish keepers would prove beyond any doubt that the fish had changed sex and become a fully functioning male.
By the time it came to be written in various forums and slightly "altered" Chinese whispers style, a new myth is born.

There are two possible explanations:

  • The female is which changed is actually still a female even though she appears more like a male. Internally she still has only female reproductive parts and is incapable of fertilizing another female. The fry can easily be explained because it is well known that Xiphophorus will store sperm and they can produce six or more broods from a single mating so unless the females have been kept in isolation from males from a very early age the chances are that most female Livebearers are pregnant almost all the time. Broods can even be delayed until conditions are favourable.

  • The other possibility especially with Swordtails is that the fish actually is a male but a slow developing one.
    Unlike most fish male Swordtails don't all start to develop their swords at a certain age, some develop quite quickly whilst they are still relatively small but others don't develop until the fish is full adult size. Incidentally the people who breed Swordtails seriously for showing ect always say that the later developing males are far superior fish yet if you watch people buying them in the LFS the young fish with the largest sword is always the one that they want.
    I have several really good books about Livebearers and this phenomenon has been very closely studied many times by many different scientist and they all state that not a single example of proven sex change has taken place which can be scientifically confirmed.

Studies have shown that in Swordtails there is an extra chromosome. In simple terms this means that some fish are born with the ability to become either sex.
Fish which appear female can indeed become active males but a fish which has ovaries and is an active female cannot under any circumstances become a male.

The Plec myths

  1. All sucker mouthed Catfish are Plecs.

    Only one fish is correctly referred to as a Plec - Hypostomus plecostomus and this fish has been given the name Plecostomus, (shortened to Plec) for obvious reasons.
    Using the same name for other species leads to confusion and possibly misinformation

  2. Plecs are algae eaters.

    They are actually omnivores, and need an omnivore diet to survive. Young fish will eat algae as a part of their balanced diet whilst older fish tend to over look algae in favour of higher quality food.

  3. Plecs only grow to suit the tank they are kept in.

    Plecs can grow to 20 inches under good conditions. Being fed a good diet and being kept in clean water with regular partial water changes will allow them to reach their potential regardless of tank size.

Myths surrounding euthanasia

Placing the sick or injured fish in the freezer allows it to drift off to sleep peacefully and painlessly.

Nothing could be further from the truth. This method was probably invented by someone who wanted to make things easier for the person carrying out the operation rather than the fish.

Slowly freezing a fish is:

  1. It is very slow, taking many minutes before death occurs.

  2. It is very stressful, it is open to argument as to whether fish feel pain but they will certainly experience a great deal of stress by being slowly cooled very much beyond the temperature that they have evolved to.

  3. Fish may or may not experience pain in the same way that we do, but when we experience pain a stress hormone is released into our blood. Scientific tests have shown that the same response is present in fish. If fish do feel pain then freezing to death is a painful way to go.

  4. Terms like "the fish slowly and peacefully drifts off to sleep" are meaningless and are once again aimed at making the squeamish fishkeeper feel better.

This is one of the most widely spread and quoted of all myths and unfortunately it leads to a lot of unnecessary suffering. See Euthanasia

The fish need a friend myth

How often do you see people going to their local shop for some fish and buying two of everything, so that the fish will have a friend.

Some fish are confirmed loners and seeing another of their own species simply antagonises them. Even some fish which are generally regarded as being good community fish can fall into this category. Gouramis generally don't like other gouramis regardless of sex. They only come together in order to breed and if the female isn't ready or is unwilling to breed she is regarded as a competitor and not a friend.
Do some research before buying any fish, try to avoid projecting human feelings on to fish because they don't have them. Only shoaling species need to be kept with others of their kind.

The Betta Myths

Siamese Fighters have to be kept alone.

Simply not true. Siamese Fighters make great community fish with gentler tank mates.
Contrary to popular opinion it is often the Betta in need of protection from fin-nippers rather than the other way round. Siamese fighters dislike the company of other Betta regardless of sex but other fish are tolerated very well.
Keeping them in a tiny unheated, unfiltered tank either in sight of other Betta or with a mirror back plate is not the way these fish should be treated

Siamese fighters can live in polluted water

Siamese fighters cannot live in polluted water any more easily than any other fish. They are every bit as susceptible to the effects of nitrite and ammonia as are any other fish.
They can however live in water with a low oxygen level because they are able to breathe directly from the atmosphere.

Siamese fighters live in puddles in the wild

They actually live in ponds, rivers, lakes paddy fields and ditches mostly amongst heavy vegetation.

A temporary puddle cannot house a permanent population of Siamese fighters because if  it ever dried up the population would be gone.

Siamese fighter live in very warm places they work at their best when kept at the higher end of the tropical temp range around 27C.
Although very tolerant their lives will be shortened if kept at constantly low temperatures in an unheated tank for example