How Much Room Do Aquarium Fish Need?

It takes self-restraint to keep from filling a brand new sparkling aquarium to the brim with colorful schools of fish. A full tank projects the aura of a happy, busy and attractive looking community. But there are strict ratios to how many fish you can keep in an aquarium. The resulting less-populated aquarium may not be as beautiful to look at, but it will have happier and healthier fish.

  1. Adult Size and Fish Behavior

    • Before determining the fish capacity of your tank, take into account the various properties surrounding the individual fish you own or will be purchasing. The fish per tank ratio depends on the type of fish; both its size and behavior. It goes without saying that tanks can hold larger quantities of smaller fish as opposed to larger ones, but the adult size of a fish (though purchased small) must be taken into consideration. Ask the fish specialist at your pet store how big the fish is expected to get before buying.

      Behavioral characteristics also play a role in how much space the fish will need. Hyperactive fish such as Zebra Danio or a Pictus Catfish will need more personal space than a slower fish, such as a goldfish. Fish suffer from stress when they do not have enough space to move. This can lead to a premature death of that fish. Discuss the behavioral patterns of any fish you plan to purchase with the attendant at your fish store. She should be able to help you determine if you have room enough for it.

    Fish-Inch Per Gallon

    • Fish experts often note the "1 inch of fish per 1 gallon of water" ratio as a safe estimate for populating your tank. However, this system then relies completely on the size of the fish against the volume of the aquarium. Tropical fish that live in salt water tanks need more space than fresh water fish, as tropical fish are more active. Take this into account as you pick out tanks, which range in size from 2.5 gallons to 180 gallons. The larger tanks require special stands and ground inspection (that much weight could possibly fall right through your floor) but are easier to maintain and can literally hold hundreds of fish.

      A 10-gallon tank filled with neon tetras that measure 2 inches each could hold up to five fish, while a 55-gallon tank could hold up to 28 tetras. On the other hand, a 10-gallon tank filled with 6-inch long freshwater angel fish would only be able to house one (two is pushing it) fish. The 55-gallon tank could hold up to six angel fish.

    Filter

    • Aside from the pure swimming-space issue, the filtering capacity of the tank needs to be taken into account before you populate an aquarium. Not all filters are created equal, and how much and how quickly it can process waste is a crucial factor. Power filters and canister filters will process less waste compared to an under-gravel filter or trickle filter. If you have a filter that works slowly, stocking the tank with fewer bodies will better maintain the health of the fish.