You have purchased an aquarium with the proper equipment, cycled the tank, and now are ready to add the fish. Where do you begin? First, research the kinds of fish that are good for the beginning hobbyist. A freshwater tank is good for a start, and you can only place freshwater fish in it. Make sure they won't grow too large for your aquarium to accommodate, won't be too expensive to feed or maintain, and only stock compatible species. Start with no more than one or two in the beginning. The easiest types are bettas, platies, goldfish, mollies, and swordtails. Ask only knowledgeable fish store professionals for recommendations.
Purchase fish only from reputable fish stores. If the tanks in general have algae, discolored water, decaying plants, or sick or dead fish, do not buy fish from that store. If anything looks wrong in one of the tanks, do not buy anything from that tank. If the fish were just delivered, don't buy them; they are stressed from travel and may develop disease. Wait till they settle in and show signs of thriving before purchasing any.
In particular, look for these warning signs in the fish: cloudy eyes, torn or clamped fins, spots or sores on the body. Ich is a parasite that causes little white spots on the fin or body. Black or red splotches, stringy growths, missing fins, bumps, and missing scales are all signs of disease. If one fish has any of these problems in the tank, they are all susceptible. If the fish is inactive when it should be active, or demonstrating behavior such as floating, leaning to one side, not swimming properly, or is not alert, is sluggish, or shivering, do not buy it. See how the fish interacts with the other fish. Do not choose a bully or a loner. If it's kept alone, see how it reacts to fish in other tanks.
Finally, ask about a guarantee. Good shops will replace fish that die within the first couple of days. Once you've purchased your fish and have taken it home, quarantine it for a few days and observe its appearance and behavior before adding it to the main aquarium. If you follow all of these steps, you are much more likely to have success with keeping happy, healthy, and long-lived fish that will bring you pleasure for many years to come.