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Buying fish right: tips for safe shopping and mail-ordering

It’s often said by experienced hobbyists that the riskiest part of looking after tropical fish is the first few days immediately after purchase. Fish that are otherwise hardy and adaptable over the long term can be delicate at first and need to be looked after especially carefully if they are to survive. The classic examples are the L-number plecs, many of which can be expected to live for many years, even decades, once they have settled into aquarium life, but immediately after import can suffer quite high mortality if not cared for correctly. In this article we’ll review the important issues behind purchasing fish from picking out livestock through to acclimating them to your water conditions and ensuring that they are feeding properly. Not to be overlooked is the value of a quarantine tank, a place to keep delicate fish apart from other species for a couple of weeks while you check it is feeding properly and keep an eye on its health.

Before you buy

Before you buy any fishes, you should buy a good fish book. Nothing beats the value of a compact encyclopaedia of fish that lets you check up on the requirements of any fish you see on your travels. It’s all too easy to buy something small and cute in the shop that turns out to be big and aggressive when fully grown. Many of the most popular fishes have their own foibles, and without making sure you can work around them, buying fishes is a risky business. Pufferfish are cute, but can nip the fins of their tankmates. Angelfish make excellent community fish, but will eat smaller fish. Yellow tangs are hardy and colourful, but they need lots of greens in their diet. Damselfish are among the best marines for beginners, but they can be aggressive.

On the freshwater side of the hobby, few books are as universally praised as the Baensch Aquarium Atlas series. Volume one, which you can buy here, covers pretty much all main species as well as a few oddballs, and covers each species in great depth. Additional volumes cover less commonly seen species, and there are also volumes dedicated to catfish and cichlids. Marine aquarists have books aimed at both the fish-only and reef-tank specialisations; with marine aquaria being so dependent on the right hardware and potentially fraught with problems, reading up on the subject before even setting up the tank is perhaps even more critical than it is with a freshwater aquarium.

Now choose your fish

There are two ways to buy aquarium fish, from a retailer or by mail order. Each method has distinct advantages. Shopping at your retailer obviously has the benefit of instant gratification, but being able to browse through the displays also gives you the chance to find new species you’ve not heard of before that might make great additions to your fish collection. By watching the fishes you can decide if they have the right temperament for your community, and you can also take into account things like size and colour. On the other hand, mail-ordering fish can give the aquarist access to a much wider range of the species than those offered by their local retailers. For aquarists interested in particular niches of the hobby, such as killifish or catfish, mail-ordering may be the only way to get hold of unusual or expensive species that retailers just don’t tend to carry.

When shopping in a tropical fish shop, it pays to choose only healthy stock. Good retailers are usually easy to recognise. The tanks will be clean, not too densely stocked, and any sick fish will be treated and dead fish removed. A shop with overcrowded tanks filled with grime and algae is a bad sign, and dead fish being eaten by the other fish in the tank is a very bad sign indeed. Health problems like whitespot will occur in even the best stores, but look to see that the stricken tanks are quarantined; if not, then buying fishes from this store is an invitation to bring problems home with you. When you’re picking out fish, look for specimens that are lively, alert, and clearly well fed. With plecs, for example, avoid specimens with sunken eyes and hollow bellies. If you’re shopping for fish with special needs, ask the retailer about their care to confirm that it has been quarantined and is feeding properly.

Mail-ordering fish is less problematical in some ways because good suppliers will ensure that healthy specimens are boxed and sent out in bags containing lots of oxygen. Some suppliers offer "dead on arrival" guarantees, and that’s usually a good sign that they have confidence in the quality of their livestock and their methods of delivery. The other nice thing about mail order shopping is you can review their online stocklists against your aquarium books or favourite fish information web site (like the database on this web site).

Regardless of which mode of shopping you select, talking things over with the retailer or shipper before making a purchase is a good idea if you are unsure about a certain fish. Let them know your water chemistry, level of experience, and what else is the tank already. If your tank contains a community of adult, territorial fish, such as damsels or mbuna, adding new fish may even be impossible. Sometimes, re-arranging the rockwork breaks up the territories allowing you to add new fish, but if in doubt, discuss with your retailer before purchasing livestock.

The quarantine tank

Having a second aquarium ready for quarantining fish is one of the wisest things any aquarist can do. In most instances, even a tank as small as 10 gallons will do, certainly for small community tropicals or dwarf cichlids. A quarantine tank doesn’t need to be anything fancy in terms of equipment or decor. It doesn’t need lights, and the substrate need only be a layer of sand or gravel that can be easily cleaned between uses. A flowerpot and some plastic plants work nicely as shelter for the fish and are easily cleaned as well. Filtration can be provided by using something as simple as an air-powered box filter stuffed with ammonia remover (zeolite) in the case of freshwater aquaria. Don’t use carbon in the filter, because carbon removes medications.

The job of a quarantine tank is to give your fish somewhere to recuperate and if required be treated before they are introduced to the community aquarium. Within a week or two of purchase any illnesses such as whitespot will be apparent and can be easily treated, and a quarantining period of two weeks is probably the shortest practical period. In many cases, a quarantine tank will also provide a peaceful environment where wild-caught fish can recover from capture and transport more effectively than elsewhere, and you can ensure that they are feeding properly before forcing them to compete with the other fish in a community tank. In the case of specialist feeders, it also gives you a chance to figure out what foods the new stock prefers. This is especially important with fish that aren’t very competitive at feeding time, such as gobies. With L-number plecs, quarantining is also the time to quickly build up their fat reserves, as in many cases they will not have eaten properly for weeks, many species being notoriously poor travelers. Quarantining also protects your existing fish, by ensuring that the new livestock is free of pathogens and parasites before it is put into the community aquarium.

A quarantine tank can also be used as a hospital tank and a breeding tank, so any money spent on setting one up is never wasted. Between uses, the tank should be cleaned to get rid of any lingering germs (there are commercial products for safely sterilising fishkeeping equipment, though DIY alternatives like concentrated salt solutions can be used as well). Sterilising kills off filter bacteria, which is one reason why zeolite is favoured in freshwater quarantine tanks. In marine quarantine tanks, you’ll need to add filter media from an established tank when setting it up.

Obviously a quarantine tank is redundant if your fish are all kept in separate, single-species aquaria.

Doing without a quarantine tank

Not everyone has a second aquarium, and not everyone quarantines their fish. Can you do without a quarantine tank? Yes, but you have to be aware of the risks and try to minimise them accordingly. Both the fish and the water it is bagged in can carry pathogens such as whitespot. Only putting the fish into the tank but none of the water it was bagged in reduces the risk of contaminating your aquarium but it doesn’t eliminate it. Many fish settle into a busy aquarium very quickly, especially if there are already others of their kind there. So adding five neons to a tank that already has a school of ten of them should work out very well, with the new fish immediately settling down and eating whatever the others are eating. But this isn’t always the case. Territorial fish, such as cichlids, may view new members of their species with a certain degree of hostility, especially if the tank is rather small, and there is likely to be (at the very least) a certain amount of squabbling as each fish tries to figure out the revised territorial boundaries. Remember, just because certain species are sold as distinct varieties doesn’t mean the fish will respect those differences. For example, blue and yellow gouramis are the same species, Trichogaster trichopterus, and the males of this species can be very waspish towards one another regardless of their colour.

Even in the best of circumstances, the new fish will have to learn to accept the food you are offering, figure out which fish are best left alone, and where it is safe to rest without impinging on another’s territory. Nocturnal feeders like spiny eels may not even feed at all during the day, at least not to begin with, so providing them with food at night is important. Under such circumstances, it can be difficult to know they are feeding if there are other nocturnal fish like catfish and loaches in the tank. So while you certainly can add new fish to your community tank without quarantining them, it does increase the workload.

Acclimating fish to your water conditions

Whether you’re introducing fish to your main tank or a quarantine tank, the basic process should always be the same: expose the fish to as gradual a change in water chemistry as possible. A few fish have evolved to handle big changes in water chemistry (brackish water fishes, for example) but most react very badly to sudden changes in pH, hardness, salinity, and temperature. Whether the fish is going from worse to better water conditions is irrelevant here, so don’t assume the fish will be happy to get out of the dirty water in the bag and into a proper aquarium because it doesn’t work quite like that. Fish adapt over time to even bad conditions, and will need to re-adapt to the better conditions in your aquarium.

The traditional way to introduce new fish into the aquarium is to place the bag containing the new fish into the aquarium unopened and leave it floating for 20-30 minutes so that the temperature inside the bag matches that of the water in the aquarium. The bag can then be opened and the fish gently poured into the aquarium. The problem with this method is that while it eliminates the problems of temperature change, it does nothing about water chemistry. So a common solution is to use a needle to pierce the unopened bag half a dozen times while it is floating it in the tank. Water will diffuse in and out of the bag, gently changing the water chemistry inside the bag to that of the water in the aquarium. This approach can work very well, but the downside is that water from the bag gets into the aquarium, dumping the load of ammonium that accumulated while the fish was being transported and potentially allowing in any swimming parasites that were in the retailer’s tanks, such as whitespot.

A cleaner method is to half-fill a bucket with water from the aquarium and float the pierced bag in that. This will allow the fish to adapt to changes in water chemistry and temperature safely, while keeping the dirty water in the bag isolated from the aquarium itself. After acclimation, the fish can then be netted out and put in the aquarium, and the water in the bucket discarded.

Some aquatic organisms are more sensitive to water chemistry changes than others, and for the most delicate species, particularly marine fish and invertebrates, the "drip method" is particularly favoured. If you are shopping for fishes likely to need this technique, it’s a good idea to ask your retailer to pack them in an oversized bag with as much water as possible. This is because you will pour the contents of the bag -- water and livestock -- into a clean bucket, and if there isn’t enough water in there, the livestock may be exposed or unable to swim properly. If there isn’t enough water in the bag, use the pierced-bag technique to add the minimum amount of aquarium water to the bucket to safely cover the livestock. Either way, release the livestock into the bucket and discard the bag. The trick now is to drip in tiny amounts of water over a long period so that the water chemistry gradually changes over time. Airline tubing and plastic regulator valves work perfectly and are very inexpensive and can be easily bought at any aquarium shop. You’ll also need some type of attachment device to hold the tubing onto the tank; again, inexpensive clips and suckers can be purchased to do the job, or else DIY solutions using adhesive tape will work just as well. Either way, use the tubing as a siphon, placing the valve at the end to control the flow so that nothing more than a drip at a time comes out. When the water in the bucket has doubled, scoop out a cupful and throw it way, and then allow the level to rise again. Do this once or twice more. The whole process should probably take about an hour, and in that time the fishes or invertebrates will have slowly and safely acclimated to the new conditions. They can then be carefully removed from the bucket and put in the aquarium.

A word about moving fish and invertebrates. Most fishes are fine exposed to air for a short while, but pufferfish can pump themselves up with air and find themselves unable to deflate themselves properly, and many invertebrates, such as sponges and sea urchins will die if bubbles of air get trapped inside their bodies. When moving such delicate animals, scoop them out of the bucket using a suitably sized container that keeps them underwater at all times. A clean jam jar or ice cream carton is ideal for this. Using plastic or glass containers instead of nets also works very well with spiny fish such as catfish that tend to get tangled up in nets. Damage to the skin following attempts to untangle them can make them vulnerable to fungal and bacterial infections. Also bear in mind that some fish and invertebrates have stings, so when transporting them, take special care to avoid touching them. Among the species known to have stings are lionfish, stonefish, waspfish, scats, numerous catfish, some sea urchins, and certain corals. Surgeonfish and spiny eels aren’t venomous but they are equipped with sharp spines they will readily use when stressed, so handle them with care as well.


On the whole plants tolerate changes in water chemistry very well, but almost always being uprooted causes some degree of shock, and most plants will shed a few leaves after they are planted in your aquarium. It usually takes a few weeks for plants to settle down, but assuming the conditions are within their range of tolerances, most plants recover from the ordeal of being uprooted and transplanted without problems. The chief exceptions are among the marine algae: most need to be acclimated to a new aquarium in the same way as delicate marine invertebrates, using the drip method. Further exceptions are among the mangroves. While most mangrove propagules ("pods") can be transported easily between fresh, brackish, or salt water conditions, once the propagule has developed leaves or roots it must be kept at whatever water conditions it was germinated under, so a salt water adapted mangrove plant can’t be added to a brackish water vivarium, or vice versa.

A unique issue with plants is the introduction of snails as unwanted pests. Of course, in tanks containing snail-eating fish such as loaches and pufferfish this isn’t so much a problem as a source of live food, but for the average planted tank, cleaning the plants before adding them is a very good idea. Various DIY methods using bleach or potassium permanganate exist, but one of the safest and easiest solutions is to use an commercially-formulated anti-snail remedy in a bucket of water. Leave the plants in there overnight, rinse the plants off thoroughly, and then put in the aquarium. Killing the snails when they are in the aquarium is much less attractive because the dead snails pollute the tank.

Preparing the aquarium for newcomers

The other side of the issue when adding new livestock is to make sure the aquarium is prepared properly. An old trick that works well is to switch off the lights for a while. This tends to calm fish down, and many territorial species, such as cichlids and damselfish, will return to their lairs. Once the new fish are added to the tank, leave the lights off for an hour or two so they will have to explore their surroundings and calm down before the other fish start badgering them.

After the lights are turned back on, adding some food to the tank can help to get things back to normal by distracting the resident fish from being too curious about the newcomers. A trick that works with territorial fishes is to re-arrange the rockwork and bogwood, forcing the fishes to re-assert their claims, putting residents and newcomers on a level playing field as far as territories go. But in the average community tank with schooling or non-territorial fishes, things should settle down quickly.

All done!

Some fishes will eat food immediately after being introduced to an aquarium, in particular small schooling species like tetras and barbs. Other fish will take hours or even days to settle in. If the fish have been quarantined, this shouldn’t be a problem because you will have already fattened them up a little. Corals and other marine invertebrates very often look off-colour for a while, and it may be several days before they return to their former glory, but assuming you’ve acclimated them carefully and that the aquarium is suitable for them in all regards, they will eventually settle down. At this point the aquarist should be looking for signs of whitespot and other opportunistic infections that might have come home with the new livestock. Examine the fins of fishes for the tell-tale small white cysts that reveal whitespot and treat accordingly. Dosing the tank proactively isn’t a good idea because the copper-based medications are known to stress certain types of fish, but making sure you have a pot of anti-whitespot potion to hand just in case is sensible.

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