Now that you have selected you tank, cycled it, and it is ready for fish, you need to go fish shopping! Browse through the assortment of fish and decide what kind of fish you would like to have. Once you find the fish you are looking for, observe the entire tank very carefully. The last thing you want to do is bring home a disease, infection, or parasite that you will have to treat.
Here are some things to watch out for:

Ich (ichthyopthiriasis) is a common parasite that causes little white spots on the fin or body of any fish in the tank. Inspect ALL of the fish in the tank. If you see any signs of this, do not buy a fish from this tank and alert the store owner of the problem.

Black or red splotches, stringy growths, missing fins, bumps, and missing scales are all warning signs of disease. Don’t buy from a tank with these symptoms.

Inactivity can be misleading. Some species of fish are active by nature; most catfish are inactive during the day. If the fish is floating, leaning to one side, or does not appear to be alert, then stay away from those fish.

Rescuing fish that are constantly being picked on is a bad idea. Those fish may be getting picked on because of an internal parasite.

Once you have found the perfect healthy fish, you need to be careful when you are adding it to your tank. You did all the research, you know what type of water and what temperature your fish needs. Now, introduce them to their new home easily.

Now that your water is just right, prepare to add them to your tank. Keep the bag sealed and float it in your tank for about 20 minutes. This helps to equalize the water temperature without shocking your fish. Next, open the bag, discard about 1/3 of the water from the bag, and replace it with water from your tank. Do this every 10 minutes for about an hour. This will help your fish acclimate to the water quality of your tank without shocking it. Next, tip the bag over and allow your fish to swim freely. congratulations! You are now the proud keeper of a hungry mouth!