The "One inch per gallon Rule"
This is more my opinion than an article.
The "One inch per gallon Rule"
No one really knows how/where this “rule” originated, but it is thought that it started in the 1960’s. During that time, there was not the immense variety of fish on sale like the ones available to us today due to various reasons/regulations & one theory is that the size of fish available then was of the type that remained small, which made the “rule” quite feasible/appropriate & it has remained. Whether it is a myth, is still being debated to this day.
Whether Myth or Fact, it is only a generalised rule, open to interpretation & not set in stone. Rules can change with the times & this one may not apply as much as it once did & many variables have to be considered. This “rule” really only applies to slim bodied, small fish that only grow to 2 or 3 inches. Many aquarists’ do not use this “rule” at all, but I do believe it is still a handy/useful guide for beginners or those keeping small fish like the aforementioned. Common sense has to come into play & the “rule” should not be taken literally & applied to all fish - you would not keep one 10 inch goldfish or an Oscar in a 10 gallon tank or ten 1 inch goldfish/Oscars in that tank.
The variables that need consideration when stocking are many:
Fish size: The Length of a fish is not the only thing to be calculated, its height/width need to be considered as well. If using the “rule” you must always use the size a fish will become when an adult, not the size it is when bought, so researching the fish first is necessary.
Behaviour: You need to know the swimming style of the fish – are they active swimmers that may need extra space. Feeding behavior – are they shy or slow eaters, do they prefer to eat from the top or bottom of a tank! Breeding behaviour – are they territorial etc. Compatibility – will it get along with the other fish, will it nip at other fish. Is it aggressive? many aquarium inhabitants may not be able to live together properly to the end of their natural life spans.
Diet: Fish may have different nutritional needs – some fish need more protein than others do. Are the fish herbivores, carnivores or omnivores? You need to know if you can meet each species requirements or is the diet of all the fish similar.
Environment: Some fish may need a planted tank, others non-planted. Lighting – some fish require very subdued lighting. Gravel or Sand – some fish prefer sand, some require very smooth gravel. Rocks/caves – some fish need rocks, caves to hide in or for breeding. Temperature - Does it like cooler/warmer temperatures? High/low PH.
Surface Area of the tank: It is normally better to have a wider/longer tank because it provides more surface space, which in turn provides more oxygen, but some fish e.g. Angelfish require a tall tank as well because of the height their fins grow to. Aquariums now come in a wide range of different shapes and sizes to meet the different swimming needs of fish. For example, 20 gallon tanks often come in “high” (24” long x 12” wide x 16” tall) or “long” (30” long x 12” wide x 12” tall) configurations.
Filtration/circulation: A good filtration system can have a bearing on how many fish can be kept in a tank, although I do not go along with overstocking a tank. Are the fish messy eaters or big waste producers? Do they require more oxygen than others do? Do the fish require a slow or fast water current?
In conclusion, it is possible I have left something out but I think you get the idea, it is not only one but many factors that need to be considered & doing research into the fish you want to keep is vital before buying them.
It is my belief that any animal whose destination is to be kept in captivity as a pet has the right to live in an environment as close to their natural habitat as possible and one that will not severely stunt its growth or shorten its natural lifespan.
Last edited by Bernie : at .