http://www.malawicichlidhomepage.com/aquainfo/tank_fish_size.html
some excerpts -
Tank Length. This is perhaps the most crucial factor in a tank, since it is the dimension which will keep fish as far apart as possible and give them the space to swim and flex their muscles – especially for cruise predators. In our opinion, the tank should have a minimum of 5x adult fish body length (FL) as its long dimension with 20 cm of fish length being the bare minimum. A further 20-50% extra length should be added if the fish is a cruise predator (+30%) or extremely aggressive (+20%) or both (50%); factors of 1.3, 1.2, and 1.5 respectively. If a fish is a poor swimmer then we can get along with just 5x without any additional length despite the aggression factor (0% additional length; factor 1).
We must emphasize the need for first class information about the species you want to keep before you build or buy the tank, and before buying the fish. On the one hand, you should add an extra 10-20% in the L value (factor 1.1 – 1.2) if you want to keep more than one specimen of the same species, while sometimes a second specimen of the same sex can’t be housed in the same tank no matter how generous the dimensions are. It is also wise to recall that, unlike mammals, for instance, fishes have indeterminate growth – there is no absolute maximum size; the fish’s growth slows down eventually, but it will continue to grow as long as it lives, given adequate food. Therefore, a published “maximum size” for a fish species may be routinely exceeded in captivity, and this too should be allowed for in sizing the tank. On the other hand, for really mild-mannered fish kept in a peaceful community tank one can reduce the 5x factor to 4x – but please make absolutely sure that the fish doesn’t become aggressive during spawning or any other phase of its life. It goes without saying that housing a predator with its natural prey in the same tank will not save the latter no matter what the tank volume is. As said at the beginning, common sense is always needed.
Thus (for a single specimen), where L = tank length and FL = expected maximum fish length :
Peaceful fish, peaceful tankmates : L = FL x 4
Aggressive fish, good swimmers : L = FL x 5 x 1.2
Aggressive fish, poor swimmers, ambush predators : L = FL x 5
Aggressive fish, cruise predators : L = FL x 5 x 1.5
Mild temperament, cruise predators : L = FL x 5 x 1.3
Pair of aggressive fish, cruise predators : L = FL x 5 x 1.5 x 1.2
some excerpts -
Tank Length. This is perhaps the most crucial factor in a tank, since it is the dimension which will keep fish as far apart as possible and give them the space to swim and flex their muscles – especially for cruise predators. In our opinion, the tank should have a minimum of 5x adult fish body length (FL) as its long dimension with 20 cm of fish length being the bare minimum. A further 20-50% extra length should be added if the fish is a cruise predator (+30%) or extremely aggressive (+20%) or both (50%); factors of 1.3, 1.2, and 1.5 respectively. If a fish is a poor swimmer then we can get along with just 5x without any additional length despite the aggression factor (0% additional length; factor 1).
We must emphasize the need for first class information about the species you want to keep before you build or buy the tank, and before buying the fish. On the one hand, you should add an extra 10-20% in the L value (factor 1.1 – 1.2) if you want to keep more than one specimen of the same species, while sometimes a second specimen of the same sex can’t be housed in the same tank no matter how generous the dimensions are. It is also wise to recall that, unlike mammals, for instance, fishes have indeterminate growth – there is no absolute maximum size; the fish’s growth slows down eventually, but it will continue to grow as long as it lives, given adequate food. Therefore, a published “maximum size” for a fish species may be routinely exceeded in captivity, and this too should be allowed for in sizing the tank. On the other hand, for really mild-mannered fish kept in a peaceful community tank one can reduce the 5x factor to 4x – but please make absolutely sure that the fish doesn’t become aggressive during spawning or any other phase of its life. It goes without saying that housing a predator with its natural prey in the same tank will not save the latter no matter what the tank volume is. As said at the beginning, common sense is always needed.
Thus (for a single specimen), where L = tank length and FL = expected maximum fish length :
Peaceful fish, peaceful tankmates : L = FL x 4
Aggressive fish, good swimmers : L = FL x 5 x 1.2
Aggressive fish, poor swimmers, ambush predators : L = FL x 5
Aggressive fish, cruise predators : L = FL x 5 x 1.5
Mild temperament, cruise predators : L = FL x 5 x 1.3
Pair of aggressive fish, cruise predators : L = FL x 5 x 1.5 x 1.2
