While waiting the few weeks it will take to make sure that your new aquarium is running properly, spend the time looking in pet and aquarium shops for the right fish. Shop around, ask questions, and most importantly, make a couple of visits to each store to see that the fish are healthy.
Once you've made your choices, read up a little on the species you like to make certain you know their temperature, pH and dietary requirements. Your first fish should be a hardy species with few special food needs. If you are planning a community tank, find out how big each fish will get, whether they swim in schools, and whether they're aggressive. Then sit down and make a shopping list.
Your first concern is the number of fish your tank will hold, the rule being 1-inch of fish for every gallon of water. The rule applies for regular rectangular tanks – not narrow show tanks or designer tanks with little surface area. A broad 1-inch fish has to be counted as 1½ or even 2 slim fish.
While this will limit your choices, the truth is that you will find a small tank with only a couple of different species enjoyable to watch and gives you a chance to observe your fish closely while becoming comfortable with good aquarium maintenance.
Best Fish for a First Aquarium
Here are some of the best candidates for a first aquarium. These are all fish that do well in waters with a pH of around 7 and a temperature of 74 to 76 degrees Fahrenheit. All will readily take flake food.
All of the above fish, except the gouramis, are schooling fish that will be less stressed and healthier if you have four, five or six of them together. Alone or in pairs these fish tend to be nervous and shy and tend to hide. The gouramis do well in pairs (and are easy fish to breed). They will, however, take up some of your choices since they grow to 4 to 6 inches.
Some of the livebearers, such as mollies and swordtails, also make good choices for the first aquarium although they tend to be less lively and often, perhaps due to poor breeding, are the first to become sick. They also seem to be easily stressed by the activities of other fish.
Tetras, another species often recommended for first tanks, are colorful and fun to watch but are not very hardy fish.