So you’re at the pet shop choosing your new freshwater tropical fish, you’ve found the ones you’d like, and are ready to purchase. Before buying, check that the shop you are planning to buy from look after their fish properly. Tropical fish get very stressed when they are moved around, and this makes them susceptible to disease, so any reputable shop will quarantine new fish for a couple of weeks after they receive delivery. I personally always like to check that the dealer has quarantine tanks set aside for this purpose, and if they don’t, do ask what their policy is regarding new fish.
Secondly, check the conditions inside the fish tanks. If they look dirty and uncared for, or you see a few dead fish around the place, I would recommend not buying from this shop, the chances are that the fish you buy from them will not live long.
If you are happy with the shop you are at, watch carefully the fish that are caught for you. You want to have healthy specimens, and this you can usually see at a glance. The top fin should be standing tall, and the fish should have a good shape, i.e. nicely rounded underneath, not concave. Check also that it swims straight and streamlined. If you are looking to breed your fish, check that you know what sex the fish is, if possible. In livebearers, which are the easiest to breed, it is usually obvious by the dorsal fin, but egg-layers are not often easy, and sometimes, depending on the species, they can be impossible to tell apart.
At this point the shop with almost certainly put the freshwater tropical fish in plastic bags that they will tie up tight with as much air as possible left inside the bag. To ensure you give your fish as little stress as possible, it is advisable to put the plastic bag inside a thick paper bag, to keep the tropical fish in the dark as much as possible.
Now, get the fish home as gently and as quickly as you can, and float the plastic bags on top of the aquarium for twenty minutes or so. This will allow the fish to calm down, and the water temperature in the bag to match the temperature in the aquarium. After the twenty minutes is up, cut open the bag and release the fish, with as little of the dirt from the water as possible. If you have a brand new aquarium you can release your fish straight in to it, otherwise I would recommend using a small quarantine tank for a few days just so you can protect the rest of your tropical fish.