Once you have allowed your new freshwater aquarium to run for several weeks without any fish in it to allow the beneficial bacteria to grow and to allow the water in your tank to cycle, it's time to start thinking about adding fish. The worst mistake you can make at this point is to run down to Ye Olde Fish Shop and buy a bunch of pretty, shiney fish and throw them into your tank. It is very important for the health and well-being of your aquatic pets for you to think through the world you are creating.

Here are some important things to consider:

• Add your fish a few at a time.
  It is important not to overwhelm your tank environment by adding a bunch of fish at once. Buy 2 or 3 fish and allow your tank to recover before you add more.
• Goldfish are never a good idea.
  Unless you are creating a goldfish tank, goldfish are not a great addition. Contrary to some popular theories, they are not even a good idea to use to cycle your tank. Goldfish are coldwater creatures and they will not do well at a tropical temperature. Goldfish also create a lot of waste. They can quickly overwhelm a new tank that is establishing itself.
• Don't over load your tank.
  An easy rule of thumb is that a freshwater aquarium will support one inch of fish for each gallon of water it contains. If you have a 20 gallon aquarium, it can support a maximum of 20 inches of fish. That means the adult fish. Fish grow. Don't buy 10 2" long fish and forget the fact that each of those fish are going to grow up to be 4" long. You have just seriously overloaded your aquarium.
  
• Build a school.
  If you decide you want fish that school, then build your school a few fish at a time. If you want a community tank, build one school and then begin to build another school of a different species.
• Lonely fish turn aggressive.
  If you select a fish that lives in a school and you don't provide it with friends, it will turn aggressive and nip other fish. Provide your fish friends of the same kind and they will, for the most part, leave their tankmates alone.
• Large aggresive fish will eat their tankmates.
  If you purchase say an Oscar and provide him with a tank of little tetras, you will eventually find a fat, happy Oscar and no tetras. Make sure you are not buying fish that eat their tankmates, unless you happen to enjoy watching fish being eaten.
• Make sure the fish you buy live in the same climate.
  You want to choose fish that thrive in the same temperature and pH levels.
  
• Properly acclimate your fish.
  Don't bring your fish home from the shop and dump them into the tank. Keep them in the bag and let them adjust to the tank temperature. Then slowly transition them by removing water from the bag and replacing it with tank water.
  

By doing a little research before you buy your fish, you will create an environment in which your fish will thrive and live happily for years to come.

The first fish for your freshwater aquarium should be tolerant of a variety of water conditions.  It is not unusual for water conditions to fluctuate during the introduction of fish, and you want your aquatic pets to have the best chance of survival as you get the hang of getting and keeping your water conditions under control.

Your first fish also need to be easy to feed and accept a variety of foods.  Don't buy a finicky variety of fish that will only eat certain foods. 

Make sure that you are not buying fish that will outgrow your tank or outgrow their tankmates.  Some varieties of fish are fine as long as everyone is the same size, but if they become larger than their tankmates, they will eat them. 

The level of agression in the fish is important as well.  Some fish only become aggressive if there aren't enough of them in the tank.  Others just don't play well with others.  Agression will cause the fish to nip at each other, and the resulting wounds can kill your fish. 

Unless you are creating a single species tank, make sure all the varieties you want to have in your community tank will live well together.  They need to like the same water temperatures, pH level and general water conditions.

Here's a list of some good first fish for your freshwater aquarium.  They are hardy fish that, with a little care, will survive the startup cycle of your tank, and will help you create a healthy environment for your fish to thrive in.

• Barbs
  Cherry, Gold, Rosy, Ruby.
  
• Catfish
  Bronze or Gold Corys, Spotted Cory, Bandit Cory and Panda Cory.
• Danios
  Zebra, Leopard and Pearl.
• Rainbowfish
  Boesmans, Neon, Celebes.
• Rasboras
  Harlequin, Scissortail.
• White Cloud Mountain Minnows