In any aquarium, regardless of its actual dimensions and volume, you should understand that the maximum number of fishes kept is in this descending order: tropical freshwater, coldwater freshwater, tropical marine. The following illustration shows the typical maximums for a 90 cm X 38 cm X 30 cm (30in. X 15in. X 12 in.) tank.

Applying the guides:
- Tropical (freshwater) fish 30cm2 per 1cm length of fish.
- Coldwater (freshwater) fish 60cm2 per 1 cm length of fish.
- Tropical (marine) fish 120cm2 per 1cm length of fish.

The comparative total fish stocks that can be held in each tank, depending on type of fish kept, are:
- Tropical (freshwater): 90 cm (36″) total fish length.
- Coldwater (freshwater): 45 cm (18″) total fish length.
- Tropical (marine): 22.5 cm (9″) total fish length.

Incidentally, when measuring a fish, only measure the standard length (SL) from snout tip to end of body – don’t include the tail.

For the newcomer to the hobby, there are excellent easy entry-level systems available from the aquatic dealer. Best described as ‘fill up and go’ aquariums, each comes complete with lighting and filtration systems and it really is a case of furnish the tank, fill up with water, plug into the electric supply and you’re up and running. Introducing the fish comes a little later once the tank has settled down.

Reading about the separate components – and their functions – that make up the whole aquarium form will not only give you a better understanding of how the aquarium actually works but it will also provide a firm basis upon which you may want to go on to plan your own, larger, aquarium in years to come.

There are also other factors to take into consideration when choosing an aquarium. Size, we have already dealt with. Most aquariums supplied for sale nowadays have to comply with certain construction standards and usually bear some kind of trade-agreed label or sticker to this effect. This is important and should not be disregarded.

Water exerts a tremendous pressure upon the glass walls of the tank. In long aquariums, the front and back panels can easily bow outwards under such pressure and to prevent this there are usually bracing straps across the top of the tank from front to back. As the volume of the tank increases, so should the thickness of the glass used in its construction; again agreed thickness recommendations are in place for aquariums made by reputable companies.

Small acrylic tanks are often aimed at the children’s market but these are usually too small for long-term fishkeeping success.

The choice between glass and acrylic is a personal one, the main perceived drawback being that acrylic scratches more easily during cleaning. However, providing the correct cleaning pad is used, there should be minimal damage caused and acrylic’s ‘formed-all-in-one-process’ does allow for some remarkable aquarium designs.

Although you should always choose the largest aquarium you can afford (for the sake of the fish, you understand), you should also ensure that it doesn’t take up every inch of its allocated space -make sure that there is enough room around, above and beneath the aquarium for regular, trouble-free maintenance tasks.

In general, most aquarium fish offered for sale will survive in domestic tap water but for those species that are a little more ‘delicate’ the fishkeeper should know something of how water quality may be defined.

Basically, all natural fresh waters originate as rain but absorb ‘contaminants’ as they fall through the atmosphere, permeate through various soils or flow over differing substrates. These dissolved materials make the water either acid or alkaline, hard or soft.

Moving a fish from an environment with one particular quality of water into another too abruptly will cause it to become stressed and therefore liable to contract disease. A typical example of this is where you may buy a fish in an area using one supply of tap water and take it home where your supply is quite different.

The point was made earlier that freshwater fishes are fairly tolerant to change but this only holds good as long as the change is very gradual, so that the fish can be acclimatized to the new conditions as slowly as possible.

pH levels and water hardness

Acidity and alkalinity form the two ‘halves’ of the pH scale. The whole range is numbered from 0 to 14: 0-7 is acid, 7-14 alkaline, with each unit being ten times the preceding one. Fish from jungle streams generally prefer acidic water as their natural home is full of fallen vegetation which decomposes in the water to give an acidic reaction. Alkaline waters usually turn out to be harder in nature. Jungle waters are likely to be soft, with few dissolved minerals. Central American fish, such as the popular livebearers are found in more alkaline waters as are fishes in Africa’s Rift Valley Lakes, which are just enormous water-filled rocky clefts.

Turning back to domestic supplies, the quality of water from the tap depends on the water’s source which may be many miles away from its eventual distribution point. Water from mountains and lakes is likely to be soft whilst water draining off chalky soils will be much harder.

Altering the condition of water is not too difficult in respect of ‘hardness’; simply diluting hard water with a quantity of known softer water (clear rainwater for instance) will bring down the overall hardness quite easily. Should it be necessary to harden the water more, then using a calcareous (calcium-rich) substrate will do the job gradually without killing the fish in the process. Changing the pH is slightly more difficult, as the degree of water’s inbuilt resistance to pH changes (known as buffering) will obviously vary due to differing basic water qualities from locality to locality, but it can be done. You must ensure that all changes to water quality are made as gradually and over as long a period as possible to avoid stressing the fish.

The importance of researching any fish’s needs before buying it will be reiterated many times. However, you can be caught out as many fish are commercially-bred thousands of miles away from their original, natural habitats. In these cases, the water requirements for the wild fish may not be the same as for the same fish that have been bred for the aquarium. Furthermore, the water parameters at your dealer’s premises are likely to be different again – so, whilst research is all well and good you have to be aware of these possible anomalies.

Lighting is essential as it stimulates all life and, of course, we want to be able to see into the aquarium. The usual light source for aquariums is fluorescent tube. Although traditional tungsten lamps (now thought outdated and inefficient) still work and have their adherents, they produce too much heat within the aquarium hood which, in turn, often shortens the life of such lamps.

The lighting fitted ‘as standard’ is adequate for fish-watching but an increase in light intensity will be needed for better plant growth in freshwater tanks and coral growth in marine aquariums. Fit more tubes, if there is room in the hood, or make better use of the light you have already got by fitting clip-on light-enhancing reflectors to the tube.

However much light you have, it won’t do any good if it doesn’t penetrate down into the aquarium. Keep the cover glass clean! Murky water will also cut down the beneficial light so make sure a filtration system is not only fitted but also maintained regularly.

You can buy different fluorescent tubes for different purposes: to enhance colors of the fish or to encourage better plant growth for instance.

Modern ‘luminaires’ – fittings which clip on to each side of the aquarium – do away with the traditional aquarium hood. These can be fitted with normal-sized fluorescent T8 tubes or the latest slimmer (and brighter) T5 tubes.

High-intensity metal halide lamps (housed in a pendant fitting) over an open-topped tank are best for large, deep tanks. You will still need a cover glass to prevent damage to the lamps from water splashes.

Keep the lights on for around 10-12 hours each day, as this is what the fish get in nature.

Too much light will result in rampant algae growth. Cut down the amount of light (either intensity and/or duration), plant more plants or introduce some algae-eating fish!

Lamps do not last forever, a fact easy to ignore. Renewing fluorescent tubes every year will ensure that your aquarium never loses its visual appeal.

Always follow the manufacturer’s instructions as accurately as possible. You will need to know the exact water volume capacity of the hospital tank (or tank to be treated). Never be tempted to add a bit more medication ‘to be on the safe side’; over-dosing can be lethal, whilst under-dosing can be ineffective.

Never go on to a different treatment immediately (if the first remedy tried failed to work) without returning the water conditions in the hospital tank to normal first. This is to avoid an accumulation of remedies in the tank, as they may react together to create a toxic situation. A further reason for this is that should a subsequent remedy prove to work, how can you be sure it was the last used remedy or a combination of all remedies you may have used?

Make sure that all equipment used in and around the hospital tank never comes into contact with any equipment used for other tanks. This will reduce the risk of cross-infections.

Should the worst happen
The fishkeeper’s responsibility to the environment also includes disposing of any dead fish. Flushing down the toilet is not acceptable as pathogens could re-enter the native water system. Incineration is preferred with burial another alternative.

Also in mind the possibilities of contaminating the water system when disposing of water during routine maintenance, should any fish in the aquarium appear diseased. Scattering the water over a wide area in the garden should ensure it ‘degrades’ as fast as possible before it seeps through the soil to find its natural way back to the water system.

Velvet
A similar disease to White Spot is Velvet. Caused by the parasite Oodinium (now Piscinoodinium) pillularis, the symptomatic spots on the fish’s body are far smaller, giving the impression of being ‘dusty’. Again the fish’s attempts to alleviate the disease are scratching, increased breathing and maybe some rusty patches of color appearing.

Treatment is to use a salt bath in a darkened tank (the parasitic spores often photosynthesize) coupled with a few degrees rise in temperature, if the fish can tolerate it. Trypaflavine is another alternative remedy, again with an increase in temperature. Amyloodinium ocellatum is responsible for Marine Velvet. Treatments include copper and freshwater dips.

Gill and skin flukes
These, literally, irritating ailments are caused by two separate, yet remarkably similar-sounding worm parasites – Dactylogyrus and Gyrodactylus. These creatures are armed with hooks by which they attach themselves to their unfortunate hosts which are soon debilitated by their blood-sucking attentions. Listlessness, loss of energy, faded color and difficulties in breathing are all symptomatic of an attack by these parasites.

Initial treatment in the hospital tank should involve a 25 per cent water change before moving on to recognized remedies such as formalin and organophophorus-based treatments, both of which should be handled with care.

Fin Rot
Not so much a disease as rather a secondary illness. Where a fin becomes split, it provides an excellent location for disease to invade. It is usually in poorly-maintained aquariums where water conditions are well below what is recommended and the tank’s overall hygiene has been neglected that such secondary diseases flourish. Transferring the fish to better surroundings usually affects a cure.

Fungus
Caused by the fungal mould Saprolegnia, Fungus is again a secondary invader after the fish has been attacked by a parasite, has an open wound and is being kept in less than perfect water conditions. The disease looks like tufts of greyish cotton wool attending the affected area. Salt baths are beneficial as are proprietary treatments allied to improved aquarium hygiene.

Mouth Fungus
Although apparently sharing similar visible description to Fungus, this particular ailment is not caused by the same fungal mould but by a bacterium Flavobacterium columnare (formerly Flexibacter columnaris). Enouraged by poor aquarium conditions, the disease should respond to treatment with antibacterial remedies.

Neon Tetra Disease
Named after the Neon Tetra in which it was first found, it is caused by Pleistophora hyphessobryconis. Symptoms are fading of color on the fish together with subsequent wastage of muscles and loss of swimming ability with death being the inevitable outcome. All affected fish should be removed and destroyed as there is no reliable remedy.

Dropsy
This debilitating disease is not a pretty sight. The scales stand out almost at right angles from the body which has become distended through the build up of fluid internally. Gouramies seem particularly prone but there is no consensus as to the actual cause or whether it is as contagious as some believe. Affected fish should be removed for risk that other fish may eat their dead bodies and so contract the disease. Possible effective treatments include anti-internal bacterial remedies. Experimental drawing off of the bodily fluid with a syringe is not to be recommended.

Hole-in-the-Head
Unfortunately, this disease is as distressing as its name implies with tiny holes appearing on the head and along the lateral line (where it is called Lateral Line Erosion). Certain Cichlids, such as Discus and Uaru, seem prone to this as are many marine fish. The cause is a parasite, Hexamita, but there are many opinions as to what triggers an attack from blaming poor conditions, stress and even carbon in filter. Remedies containing Metronidazole are said to be effective.

Shimmying
Sometimes you see a fish, especially Mollies, standing on the spot and gently swaying from side to side. According to some, this is not a disease, or anything affecting their balance, but merely their reaction to cool temperatures as raising the water temperature usually makes them stop doing it. Other sources feel that this may be the onset of symptoms caused by a massive invasion of many pathogens and bacteria, requiring at least a salt bath and perhaps the use of a proprietary remedy.

Swimming Disorder
Where a fish cannot maintain a definite position in the water, for instance, bobbing up or down, or tumbling head over heels when swimming then this is due to a malfunction with the swim-bladder. It is not an uncommon ailment in Fancy Goldfish, where the internal organs have been forced into restricted space due to the desire for a certain body shape on the part of the fish breeder.

Sometimes other internal disorders such as indigestion, can have a knock-on effect on the swim-bladder. Here, the remedy is to feed a wide and varied diet (including live foods) and to add a light laxative, such as Epsom Salts, to the food to clear any digestive tract congestion.

There are several extensions to the Goldfish theme for, although only consisting of one variety, Carassius auratus, many years of aquarium breeding have produced several different strains. The London and Bristol Snubunkins are the two most basic ‘improvements’. The London has a shorter tail against the Bristol’s well-developed broad-lobed tail but it is in the color development where the attraction lies. Pigmentation under the skin produces violets, blues and reds which, coupled with the non-reflectivity of the scales produce a wide range of colorations quite distinct from the single red/orange color of the metallic-scaled Common Goldfish.

The Comet, another metallic fish, has a large forked tail almost as long as the body. This specie can swim at high speed but only for short periods.

All of the varieties are suitable for both aquarium and pond culture. They are known as ‘singletails’ as the tail fin comprises a single unit. The following varieties have double tails and are known as ‘twin-tails’.

From here on, the traditional Goldfish body shape has undergone further development and has become more and more egg-shaped. By further selective breeding, more flowing fins have been added, in some cases the dorsal fin lost, eyes have become telescopic and tails flattened and curved almost horizontally.

These varieties form the bulk of the Fancy Goldfish interest and include all the colorations and scale patterns. There is even a jet black Goldfish called the Moor.

Typical Fancy varieties are Fantail, Veiltail, Jikin, Ranchu, Ryukin, Wakin, Oranda, Lionhead, Celestial, Bubble-eye and Tosakin and each variety has its own characteristic qualities.

Most of these varieties are not suitable for pond culture and will have lost much of their swimming prowess. Their internal organs will have become cramped through the shaping of the body with the result that some will develop swimming or balance abnormalities.

Other coldwater fishes
Whilst there are many other species of coldwater fish suitable for aquarium culture, recent legislation has made the importing, selling and keeping of such fishes much more difficult, especially those fishes imported from other countries. The reason for this is quite simple: because the fish share the same water conditions in their country that exists here, any imported fish that is set free into our native waters could seriously affect our own native fish stocks, either by predating on them or by breeding at such a fast rate that they are outcompeted for natural food.

At the time of writing, licences are required to be held by both the vendor and purchaser in respect of non-native fishes. Those fishes most affected are many found naturally in North American waters; these include Pimephales, Cyprinella, Lepomis, Notropis, and Umbra, all very attractive aquarium subjects.

Cichlids come in diverse shapes, sizes and colors originating in Central and South America, Africa and Asia. Central American species are generally the tough guys; South America offers the highly-colored Apistogramma genus, the stately Discus and everyone’s favorite, the Angelfish. Not to be outdone, Africa holds its own with the dazzling colors of its Rift Valley fishes, many of which are endemic to each particular lake. For a region so normally blessed with fishes, Asia is a poor third with only two or three Cichlids native to its waters.

So there’s an ample choice to attract you, but the real attraction for most fishkeepers is that these fish are parents par excellence. All cichlids are egg-depositors, females laying their eggs on a firm surface for the male to fertilize, but there are variations on this basic premise. The majority are happy to prepare a spawning site in open water, then fertilize and defend their hatching eggs against all-comers. For the fishkeeper, this makes a very watchable process.

Taking parental care a little further, some species get very secretive about their breeding and prefer to do it in the privacy of a rocky cave, a flowerpot or even a vacant large shell, well away from their owner’s prying eyes.

Others, some African Lake species, only just make it into the egg-depositing category; in these cases, the female does lay eggs (usually in a depression in the substrate) but then as the male fertilizes them she picks up the eggs and incubates them in her throat cavity until the young fish are developed enough to swim free. Even then, her task is not over for, at the slightest threat, the fry all dash back into her mouth for safety.

Another feature of Cichlids, is that the fry of Discus is noted for finding its first food in the mucus covering of its parents’ skin. When one parent has had enough of being a feeding station the fry are flicked towards the other to continue their meal.

Caring for Cichlids is both straightforward and complicated, depending on which species you choose. Central American and African Lake species are hard water loving, whilst South American fish are better suited to soft water; Discus require more stringent water management than most.

Feeding is no problem as most are omnivorous although some African Lake species will need green matter in their diet as they normally graze on algae-covered rocks in their natural home.

As you can appreciate, tenancy of territory plays a strong role in these fishes’ life style, so any aquarium destined for Cichlid inhabitants (and they occupy all levels) must be large enough to give each fish their allotted space – or there will be constant skirmishes between rival house-hunters.