Buying new aquarium fish can be a great deal of fun, but it shouldn't be done without forethought. Choosing healthy stock appropriate to your aquarium and skill level is the only sensible way forward.  

Know your limits

Before you buy a fish, you should be reasonably sure you'll be able to keep it alive. Too many people buy fishes that have no chance of maintaining, with fatal consequences for the poor fish. If you're starting out in the hobby, then it is a good idea to stick with tried-and-trusted species eminently suitable for inexperienced aquarists. Ideal species for beginners include:

• Pearl and zebra Danios, Danio albolineatus and Danio rerio
• X-ray tetras, Pristella maxillaris
• Bronze and peppered Corydoras, Corydoras aeneus and Corydoras paleatus
• Bristlenose Plecs, Ancistrus sp.
• Platies, Xiphophorus maculatus
• Wild or feeder guppies (as opposed to fancy guppies), Poecilia reticulata
• Thick-lipped Gourami, Colisa labiosus
• Female three-spot gouramis, Trichogaster trichopterus
• Golden barbs, Puntius semifasciolatus

All of these species can be expected to survive occasional failures in maintaining water quality, and none of them place particular demands on the aquarist in terms of temperature, pH, water hardness or salinity. None are likely to cause problems in terms of social behaviour either, and on the whole these species can be completely relied upon to be good community fish.

On the other hand, try and avoid things like angelfish and fancy guppies, however pretty you think they are. It'll take you a good six months to not only stabilise the water conditions in your aquarium but also to hone your fishkeeping skills. Nothing will ruin your enjoyment of the hobby faster than having to deal with constantly sick or dying fish. Once you've succeeded in keeping your first set of fishes alive and well, then by all means stretch your wings a little and buy some of these more demanding fish; just not right now!  

Make sensible decisions

Fishkeeping is a lot easier if you select fish appropriate to the size of your aquarium and the sort of water chemistry you have; see: Freshwater Livestock.  

Picking out healthy fish

Part of the art of selecting healthy stock is knowing what to look for. Experienced hobbyists can tell at a glance whether a fish is in perfect health or not; for less experienced (or less diligent) hobbyists it is quite easy to end up with below-par livestock.

In general fish should be alert and active. Schooling fish should be reacting to one another; when schooling fish get sick, one of the most common symptoms is that they stop schooling with their tankmates. Fish like puffers and cichlids are well known for their intelligence, and this should be apparent: they should react to your presence, ideally swimming to the front of the tank to beg for food.

Look at the fins and body: these should show no signs of damage. While fish will grow new scales and fin material without much fuss, simply being damaged in the first places exposes them to secondary infections such as Finrot and Fungus. This is critically important when selecting fish like stingrays and spiny eels that are notoriously sensitive to bacteria in the water and very difficult to treat once sick.

The following table outlines most of the more popular types of fish together with key things to look out for.  

Things to have the store clerk do

Take care that the fish do not all get dumped in one small bag. A small fish bag can safely hold 3-4 guppy-sized fish for several hours without problems; a larger bag something the size of juvenile angelfish. Spiny fish should always be double-bagged in case the first bag gets punctured. All Percomorph fish (cichlids, gouramis, glassfish, etc.) are spiny, so they should definitely be double-bagged. Other fish equipped with spines include catfish, loaches and spiny eels.

The best stores "top off" the bags with oxygen instead of air. Some stores will only do so if asked: ask!

Once the bags are tied, they should be wrapped with newspaper or brown paper. This keeps the fish in darkness, calming them down. If the clerk doesn't wrap you fish, ask him to do so.  

Getting your fish home

The prime issue when transporting fish is temperature. Up to a point, fish will tolerate gradual changes in temperature quite well. This does vary though: cichlids get stressed very quickly when exposed to cold, whereas Corydoras and Danios are much more tolerant. But excessively high temperatures can cause problems too, so either way the essential thing is to try and insulate the fish away from the ambient conditions between the store and your home. On a mild day this isn't too much of a problem, and so long as you get home within an hour or so you should be fine. But on very cold or very hot days, you will need to insulate the fish bags.

The best way to do this is to place the fish inside an insulated travelling package of some sort. Polystyrene boxes are the standard items for this, and most fish are shipped in such boxes. If you have a lot of fish, or big fish like stingrays or discus, then asking your retailer for one of these boxes would be entirely appropriate.

Insulated lunch boxes and coolers can be used for smaller quantities of fish. If all else fails, putting the fish bags into a ruck sack or similar swaddled with towels or t-shirts should do the trick. Resist the temptation to open the bags or boxes on the way home: insulation works by trapping air, and every time you open them up, you'll be moving the air and reducing the degree of insulation.  

Once you get home

Ideally, new fish will be but into a quarantine tank rather than a community aquarium, but either way the fish cannot be dumped straight into the aquarium. The aim is to acclimate the fish to the temperature and water chemistry of the aquarium without any of the water from the pet store getting into the tank. The water in the bag will, by now, be laden with ammonia. It is also a potential source of disease, though realistically so is the fish, hence the need for quarantining.

The easiest way to acclimate the fish to their new home is this: Siphon water from the aquarium into a bucket, filling it to about 1/3rd full. Place the bag in the bucket, unopened, and let it sit like that for 10-15 minutes. This will bring the bag very gently to the temperature of the aquarium. Now open the bag, and very gently add half a cup of water from the bucket into the bag. Let it sit like this for about 5 minutes, and then repeat. Do this 3-4 times in total, and then gently up-end the bag so that the fish swim into the bucket. Add another cup or so of water from the aquarium into the bucket, and repeat a couple times more, spaced out by about 5 minutes. By the end of this the fish should be reasonably well acclimated to the conditions in the aquarium. It is a good idea to place a towel or lid on the bucket though this whole process: some fishes are very likely to jump out!

Now turn off the lights in the aquarium. This will calm down the community fish. Net the new fish from the bucket and place them gently into the aquarium. Take care not to drop them into the water; instead lower them gently into the water and let them swim out of the net. Keep the lights off for the next 30-60 minutes. This will encourage old and new fish alike to remain calm.  

Acclimating brackish water fish

Unlike either freshwater fish or marine fish, brackish water fish have evolved to deal with sudden changes in water chemistry. So while the aquarist certainly does need to ensure new brackish water are not exposed to big differences in temperature, the idea they need to be carefully adjusted to different salinities across days or weeks is a myth. Truly euryhaline fish such as scats, monos and mollies can be switched between freshwater and seawater (or vice versa) in less than an hour. Put them in a bucket with the water they travelled in, and then across the next hour add small amounts of water from the aquarium at periodic intervals.  

Quarantining

Quarantining freshwater fish is critically important where species intolerant of medications are being kept. Stingrays, clown loaches and Mormyrids (Elephantnoses) are the classic examples of freshwater fish that are poisoned by the medications used to treat Ick and other common parasitic infections. Most freshwater invertebrates, including shrimps, will also be killed by these medications. Any fish added to aquaria containing these species must be quarantined before introduction.

The process of quarantining freshwater fish is essentially similar to the quarantining marine livestock. A 10- to 20-gallon tank is generally adequate for quarantining small community fish; obviously larger tanks will be needed for bigger fish. The tank will need to be filtered and heated, but things like lights, plants, gravel etc. are redundant and in fact not all that useful. You want a clean, easy to maintain aquarium. Zeolite can be used to remove ammonia directly if you don't have a biological filter mature, but otherwise a simple air-powered bubble-up box filter containing some of the biological media taken from the established aquarium will do the trick nicely. The water chemistry in the quarantine tank must be identical to that of the main aquarium.

Quarantine new livestock for at least two weeks for tropical fish and at least four weeks for coldwater fish. This will give you enough time to see parasites like Ick and Velvet if they are present. There is no advantage to quarantining tropical fish for more than four weeks or coldwater fish for more than six weeks. Use this time constructively: get the fish feeding, and if necessary, wean them onto alternative food items. Herbivorous fish are often sadly underweight (critically so among the smaller Loricariids) so make sure these fish have algae and greens to graze on.

This is also the time to deal with any physical trauma following shipping and transportation. Treat for Finrot and Fungus proactively rather than waiting for symptoms: if you see tatty fins or scratched scales, treat with a suitable medication. Melafix may be adequate for this as a preventative, but if you see symptoms or are concerned about the wound being potentially serious, treat with something more high power, either an antibiotic like Maracyn or a copper-based medication such as eSHa 2000.  

Settling fish into the community tank

Once fish are placed in the community tank they should settle down at once. Schooling fish and catfish are typically no bother at all, but sometimes territorial fish, particularly cichlids, cause problems. An old and usually effective trick is to rearrange the decor of the tank when adding fish containing territorial species. This breaks up the existing "status quo" and gives everyone in the aquarium a chance to define new territories.

Of course, this approach can't work miracles and it is good advice to always add the most territorial fish last. This is especially true with things like Mbuna, which tend to be very aggressive towards newcomers even if you move all the rocks about.  

Feeding new fish

You should have determined the appropriate food items for new fish before purchase, so there shouldn't be any surprises at this point. But wild-caught fish can be fussy about their food.

Herbivores are relatively easy to deal with: Sushi Nori, cucumber skins, sliced zucchini, tinned peas and so on can all be used for them. Because these foods are low in protein they pose little risk to water quality, and it is a good idea to use them generously, at least to start with. Wild-caught Loricariids are notoriously likely to be underweight upon purchase, and once they get below a certain body mass can be very difficult to redeem.

Carnivores are a bit trickier. While very few fish traded as aquarium fish resolutely refuse to eat anything other than live fish, many fish would certainly prefer to be given live fish instead of dead or frozen foods. For these fish, your job is to find safer alternatives (live feeders being even more likely to introduce diseases into your aquarium than the new fish!). The two staples for this are earthworms and river shrimps, both of which are enjoyed by practically all carnivorous fish and carry virtually no health risks at all. Spiny eels and stingrays especially love earthworms, and these are by far the best foods to fatten them up. Once settled in they can then be adjusted to a wider range of foods items including frozen bloodworms and seafood of various types. To a degree, it is a question of teaching carnivorous fish that you the fishkeeper are a source of food: once that happens, they're more likely to sample novel food items you offer them.

Omnivorous fishes like tetras and barbs are usually no problems at all.  

Close

This careful approach to selecting and introducing new livestock will minimise your losses. Most problems with new fish come from people selecting unhealthy fish or fish inappropriate to their skill level or aquarium conditions. But how you transport the fish home and what you do once you arrive makes a difference too. While quarantining fish isn't an option for everyone, it is the ideal, and highly recommended for anyone keeping "advanced" fish species.