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So, How Much Space Does My Fish Need?

Aquarium Dimensions and Space Necessary for Fish

(The First Tank Guide)

The most common consideration people give when determining the population of their fish tank, or whether a tank is a suitable home for a particular fish is the volume of the aquarium in question. However, this is not the only concern when determining what is suitable housing for your fish.

Space for the Fish to Move

A very important factor to consider when determining whether a fish can safely be housed in your home aquarium is the adult size of the fish when compared to the dimensions of the tank.

A 48" Arowana, for example, may be able to have enough oxygen and have his waste efficiently processed in a 50 gallon tank, but if the tank is only 12" deep and 30" wide, the fish does not have room to move around. This will cause unnecessary stress and suffering.

Make sure that the minimum dimension of the fish tank (in length (that's side-to-side) and depth (that's front-to-back)) is at least 80% of the normal healthy adult length of the fish. If the fish is a particularly inflexible fish, this minimum dimension may need to be as much as twice the adult length of the fish to insure that the fish can comfortably turn around without problems.

The other dimension (probably the length) of the fish tank should be 7-12 times the healthy, mature adult length of the fish. This should give the fish plenty of room to swim back and forth.

Also check that the height of the tank is at least twice the height of the adult fish. This means from the bottom tip of the anal fin (the one single fin on the fish's belly) to the top tip of the dorsal fin (the fin in the middle of the fish's back). That dimension is going to be a little harder to track down since most fish books don't bother to list that length... In most fish it will be quite a bit smaller than the length of the fish, and usually this just isn't an issue since usually a tank that meets the length and depth requirements (see above) will be more than tall enough for the fish. However, there are fish like Discus and Sevrums which are nearly round, and even more extreme are fresh water angel fish, where the height of the fish can be four times their length or more!

Fish Behavior and Necessary Aquarium Space

It is also important to remember the fish's behavior when determining whether it will fit in your tank or not.

A very active fish, like a Zebra Danio or a Pictus Catfish, will need more swimming space than a less active fish, like a Lionhead Goldfish or a Tiger Oscar. Make sure that the length of your fish tank is sufficient that your more active fish can have plenty of "run" (room to just swim without having to turn around), and will be able to do something other than just pester the other fish in the tank.

Another consideration related to physical space and fish behavior is territoriality. Some fish are territorial, while others are not. Territorial fish may only defend their territory from members of the same species or similar species, while others will chase any fish out of their territory. many fish will stake out smaller territories in an aquarium than they would in the wild, but some will not. It is important to know whether the fish you are selecting will be territorial or not, and if so, how much of your fish tank is that fish going to stake out and defend from intruders. Making sure that your tank is large enough for any territorial fish to mark their own spaces and do so without overly interfering with each other will be important to maintaining a healthy aquarium.

It is important to provide each fish with enough space to reach a healthy, normal adult size. Your tank will be easier to care for and your fish will stay healthier if you provide enough room in the tank for the fish to properly mature. Providing quality maintenance of the tank, including regular water changes and the necessary care for the filter, will reduce the risks of keeping a fish in a tank that is too small, however, the only solution to this problem is to be sure that your tank has enough space for the fish that you are keeping.

"What a great site! Thank you so much, it has been very helpful. I just set up an aquarium for our kids, and I really had no idea what I was doing. I wish I had found your site first. "
February 19, 2008
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"I simply wanted to thank you for putting up this stuff as it really helped me to set up my first aquarium. I've been to different sites but nothing like this. Nice work, keep it up."
August 20, 2008
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