How to Choose Easy Fish for an Aquarium

For those who hate noisy pets, fish make an excellent choice
For those who hate noisy pets, fish make an excellent choice (Image: rasbora image by pearlguy from

When starting off as an aquarist (one who keeps live fish), you want to begin with hardy fish that will not die easily, fish that are not finicky about what they eat and pets that can live in varying water conditions. Cold-water freshwater fish make excellent starters, as tropical fish are far more delicate. Make sure you have a reliable fish retailer near you and remember that the size and number of fish you keep in your tank depends largely on the size of the tank.

Things You'll Need

  • Tape measure in centimeter gradients
  • Calculator
  • Nearby pet or retail fish store

Decide how many fish your aquarium can accommodate. To determine this, measure the length and width of your tank in inches and multiply the numbers to determine the number of square inches of surface area. For slender fish (such as guppies, usually about an inch long), plan for one inch of fish for every 12 square inches surface area; for wider fish (such as goldfish, generally 1½ to two inches long), make it one fish for every 20 square inches surface area. (For instance, for a tank measuring 14 by 24 inches, the surface area is 336 inches. If you choose guppies for your tank, divide 336 by 12 and the result is 28 inches of fish, or 28 guppies. If you want to populate your tank with gold fish, divide 336 by 20 for a result of 16.8--or round up to 17--inches of goldfish; divide this by two inches per fish for a safety factor and the result is eight or nine goldfish.)

Start by populating your tank with smaller schooling fish. To insure normal behavior and avoid having shy fish that perpetually hide, have a minimum of six of each species you choose. Danios, guppies, tetras, goldfish and rasboras are among the most popular varieties and provide a nice mix of sizes and colors.

Select fish that school in different regions of the tank. While tetras and guppies prefer the top waters of aquariums, danios and rasboras will patrol the middle regions and catfish will stay near the bottom.

Buy at least one algae-eater to keep your tank clean. The plecostomus is an excellent and popular choice for this task.

Build up your schools gradually. When buying schooling fish, choose only a couple of each species at a time and add to the number every few days to each week. Otherwise, poisonous levels of ammonia from the fish excrement can kill the fish before the tank can build up healthy levels of beneficial bacteria to metabolize the ammonia.

Be consistent with the level of aggressiveness in the fish you select. If you wish to mix aggressive with non-aggressive fish, start with peaceful fish and make sure that the more aggressive fishes are smaller than their placid cousins are. One of the most beautiful midsized peaceful fish is the betta, or Japanese “fighting” fish. While having more than one in your tank will lead to interspecies fights, alone they are quite docile.

Choose hardy species for your tank. Delicate fish can die with little provocation. Some of the more rugged schooling fish species that make excellent starter fish include danios, cherry barbs, corydoras catfish and rasboras.

Tips & Warnings

  • Inspect the fish you buy for spots or sores that may indicate disease. Do not buy fish that appear to be struggling in the pet store. Start with a small tank and buy a bigger aquarium once you find that you can maintain the smaller one without killing your fish unintentionally.
  • Because the surface area of an aquarium determines the amount of oxygen and carbon dioxide exchange between the water and the air, the surface area of a fish tank matters more than the gallon capacity of the aquarium when determining how many fish your tank can hold.
  • You can keep more fish in your tank than the guidelines permit (surface area divided by either 12 or 20), provided you exchange the water in the aquarium twice a week or more and use an activated charcoal filter to help remove ammonia from the water.
  • Wider fish excrete more ammonia than narrow body fish do. This explains why, when calculating how many fish your tank can hold, you divide the surface area by a larger number for wide body fish.

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