Fish: Tropical fish

Little tropical fish can look very appealing as they sparkle and dart around mock chateaux and through fronds of weed. Big fish have a certain dignity, as they swim in a stately, leisured way. Fish seem to have simple lives and promise us endless evenings of unwinding from stress. achieve this goal, you need to think about how to create a healthy environment. and which fish you put in it.

Setting up a fish tank

The fish themselves are actually quite cheap compared to the cost of setting up a decent-sized tank with heater and thermostat, thermometer, filter system, gravel, and lid with light. It is worth investing in a good-quality system, since it will be less prone to failure. Ideally, you should have a back-up heater, in case your heater breaks down outside shopping hours. A water testing system is useful, as is a net for catching fish, an algae scraper and a 'hoover' type apparatus or detritus sucker, for removing floaty brown bits of decayed matter that collect on the bottom .

Running costs for an aquarium are quite cheap. You may need a lot of plugs, but actual electricity consumption for a tank 70cm to around a metre long is low. Dried flaked fish food lasts a long time because it should be used very sparingly, no more than can be eaten in ten minutes. Some fish like chopped worms, which are of course free. You can breed other live food, like water fleas. You do need to budget some time to clean the tank every week.

It is tempting to go into a tropical fish shop the same day you buy the tank and buy 'five of these' and 'five of those', populating the tank before it is ready, and ending up with more fish than your tank can comfortably hold. The fish are more likely to survive if you are patient. So, set the tank up, put plants in, and leave it all to settle for a couple of days. Tap water contains chlorine which evaporates, so there will be changes in the water chemistry, making it friendlier to fish.

Check how big the fish are likely to grow. Most fish shops sell mainly juveniles, which can double or treble their length over a year or two. You can calculate how much a tank will hold in terms of 1cm fish per 1 litre water, as a rough guide.

Test the water you are using for hardness and acidity so that you know what you are offering your future guests. Limestone rocks will leach lime and make water harder, so check that any rocks you add are suitable for the type of fish you want. You can collect rain water if you want soft water.

Heat rises, so the heater is best placed near the bottom of the tank, and the thermometer will measure a higher temperature at the bottom than at the top. It may take a while before you work out how to adjust the heater for the temperature you want.

It's a good idea to connect your light to a timer which changes the fishes' lights whether or not you are at home, and doesn't stress them with an extended day just because you happen to go out drinking and arrive back too relaxed to remember to turn them off. A twelve-hour day can be set on the timer. There is less variation between daytime over the seasons in tropical countries, so this setting can be maintained over the year. It is kinder to cover the side of the aquarium if you decide to keep your room lights on and party until three, since the fish may want to get some sleep.

Choosing fish

Fish vary in terms of the termperature range they prefer, and the water type they prefer . Some like hard water, others soft, some like alkaline water, and others acidic, and there are a few species which are undemanding. Guides to species usually include this information, which should be among the criteria you use when selecting fish. It is easier to keep fish healthy if you choose a selection which like similar conditions.

You can choose to specialise in one particular type of fish, or set up a community tank. The specialist route is relatively simple, so long as the fish are of a type that tend to shoal, rather than fight each other, or you just keep one.

Creating a community tank involves thought, and impulse buying is dangerous! That interesting looking catfish that adds an exotic touch might come out at night and chomp on its sleeping neighbours' tails. Tiger barbs are notorious for nipping bits out of their neighbours. Zebra danios, in their pin-stripe suits, may be considered too ordinary by some fishkeepers, but, they are among the gentlemen of the fish world, and will not commit such crimes.

Some fish are happy living a solitary existence, and do not bother other species, while others need to live in a shoal to thrive. Shoals can also be more entertaining, since the fish interact and dance with each other. Guppies, cheap and cheerful fish with tails like silk scarves, can be especially entertaining in their shoals.

There are a few species which need more space than the average tank can offer, especially fast-mving large species that like to live in shoals. Silver sharks are an example, though they are a temptation since they are such beautiful fish. Wait until you can afford to cover an entire wall with tanks for these!

Nocturnal fish are generally less entertaining since you only see a vague outline of the fish after the light is out.

Fish live at different levels, with some darting near the surface, and others keeping near the bottom. A mix of top-swimmers and bottom-dwellers means that there will be interesting things happening in different parts of the tank.

So, go to the fish shop, and look, but think hard before you buy!

See also:

         Care of pond fish

          News and Research: Fish and Marine Invertebrates, General

News and Research: Fish and Marine Invertebrates, Health, disease and physiology

Reviews of books on fish:

Fish on stamps:


Fish: Pond fish

There is a wide range of fish that can survive outdoors through frost and snow, but remember that you want to be able to see the fish, and dark, mottled, or black fish are less visible. You can go the hassle-free route and just pick the healthiest-looking goldfish or golden orfe you can find (free from white spots, fungus or damaged scales) or go the whole hog and read up on Koi carp, though these fish can be very expensive.

Setting up the pond

Generally it is a good idea to have a fairly deep pond, so that your fish can escape more easily from predators, like cats and herons, and are less vulnerable if the surface ices over. The fish will need to be able to hide away under plants (water lilies provide surface shelter, as well as looking pretty) and need water weed to browse on and for oxygen. You can build little caves for your fish, though make sure that the caves are stable, and the fish are not likely to damage themselves by dislodging rocks. Small fountains and other moving water features are useful for helping to aerate the water in summer, though they are not necessary if your pond is large and partly shaded. It is important not to overstock your pond. You need at least 30 sq cm per 2.5 cm of fish, from mouth to tail tip. Koi carp, which can grow up a to metre long, need ponds at least 1.5 metres deep.

Fish being transferred from aquaria are best transferred in summer, when the water is warmer, so it is less of a shock for them. Give new ponds a month or so to stabilise before you put the fish in. You can get fish used to the pond water before putting them into the pond by mixing it with the water they arrive in, in a bucket or other container, placed in a shaded spot, and leaving the fish for half an hour or so. Some people advise floating the bags fish are bought in for an hour on the pond surface, to equalise the temperature. This may not be a good idea if it means keeping a fish in the bag in a small amount of water on the sunlit surface of a pool. The fish may not have enough water for its needs, and will probably only start to relax once it can dart away and hide somewhere.

Keep the pond free of falling leaves and other debris, which can lead to methane-producing silt if left unchecked for long periods. Some types of weed also have to be kept in check so that they don't clog up the pond, leaving the fish little space for swimming. Canadian pond weed can be fast-growing, for example.


There is a wide range of fish food available, but use it sparingly. There is more risk of overfeeding the fish than letting them starve, especially for smaller goldfish in a pond. If the fish move away and there is still uneaten food, cut down what you give them.


Pond fish are less likely to suffer from infectious diseases like whitespot if they are given enough space. You can try treating infected fish with various preparations. It is also a good idea to isolate infected fish, and to put new fish in a quarantine tank or pond for a fortnight or so, before letting them join existing fish. Wash all new weed thoroughly to help prevent infection.

Leeches, dragonfly larvae, and frogs can cause problems for pond fish. Check weed for leeches before putting it in the pond, because it takes a long time to clean a pond once they establish their presence. Dragonfly larvae are nasty, vicious, carnivorous creatures without the grace of the adult, and should be removed if spotted. Frogs can get carried away and try to mate with goldfish, so are best kept separately. You can set up a separate pond for frogs, or try to find them another home.

Cats and herons are a bane for pond fish lovers, and you have no option but to cover your pond with a strong mesh if these are a problem. Locating the pond near your house will help to deter herons, though it does not deter cats. Large fish in relatively shallow ponds have 'dinner' written on them in neon lights, so give your fish plenty of depth to escape into, and hidey holes, like clay plant pots on their side, or other artificial caves. You may not always be able to see them as easily, but they'll be around for longer for you to enjoy them!

See also:

          Care of tropical fish

          News and Research: Fish and Marine Invertebrates, General

News and Research: Fish and Marine Invertebrates, Health, disease and physiology

Reviews of books on fish:

Fish on stamps: