I know of the 1 inch per gallon of water stocking rule for aquariums. However, there is a lot of conflicting opinions about it. So I was just wondering what other fish keepers had to say about the rule.
I won't be using this to stock an aquarium or anything, I was just wondering about others thoughs on the matter.

Small fish such as mollies, guppies, and tetras are perfect for that rule as it gives the necessary space for swimming and other needs.

Medium and Large fish however, do not follow that rule. Many large fish need space to roam and feed. Fish, depending on temperament and species will sometimes stake out territories.

For example. in a Large breeder tank i have 6 small (2.5 - 5 Inch ) Yellow Bullhead Catfish. Each catfish has a specific territory and needs that space to grow and thrive.

pets question and answers,www.5d2d.com

Fish can become stressed if they are not allowed a proper and personal living space. this space, once again depends on size, species, and numbers of that species in tank. (larger numbers of the same species can increase the amount of space required because the fish will view the other members of that species as competition.) When fish become stressed they will easily succumb to sickness and disease.

For a healthy and well balanced tank, consider the sizes of the fish, the number of fish , and the habits and tendencies of the species you select.

i hope this Helps you .

~ Dan B

I think you should decide after giving it some thought.

Do you think a 12 inch fish fits in a 12 gallon tank?

Do you think a tank that is 1 foot wide and 2 feet tall has the same swim space as a tank 2 feet wide and one foot tall?

Do you think a tank that gets 30% water changes can have the same stock as a tank that gets 10% once per month?

Do you think a calm, slow fish uses the same amount of space as an energetic and fast fish?

Do you think a territorial fish can live in as small a space as a peaceful fish?.

Do you think a tank with a small internal filter can handle the same loa as one with a big canister filter?


Basically what I'm trying to do is make you think of the different things that impact stocking, so you can use research and common sense over blind rules of thumb.


And yes, the rule does happen to work with small fish, in standard aquariums, with decent standad care.

Hi. My thoughts are that the rule of 1" of fish per gallon was a very general rule used over many many years ago and has unfortunately followed with the hobby.
I read books and surf the internet, and haven't come across this as a guide in recent decent aquarium literature lately.

The hobby and trade has grown, the types of aquarium fish that are available to us nowadays is vast, the 1" of fish per gallon rule just wouldn't work with all of them.

I could however see this rule working if all that you were stocking would be relatively small community fish like tetras, barbs, live bearers etc. Or the types of fish that were available in the early years of aquarium fish keeping.

Old enough to see the changes in the hobby......(good ones)

This rule is for pet store keepers to tell their buyers to HOPEFULLY get them to not cram them in a small space. pets question and answers,www.5d2d.com

And the rule is also very confusing. Most ppl think "I have a 1" goldfish in a 1 gallon bowl!" The "rule" should be "1 gallon per 1 inch of FULLY GROWN FISH" to give them a chance.


The rule is completely false. Research fish first and decide their tank requirements then.

Nay. Even for many small fish. There are so many things besides size that needs to be taken into account, such as temperament and/or sex. For instance, with dwarf puffers, which only get about an inch long, they need about 5 gallons per fish because they are territorial. And also with that rule, you should have 1 male and 2 females if you want 3 fish so two males aren't competing.

I'd say nay in a big way. After all, a 12 inch goldfish in 12 gallons? :S
I prefer just researching the requirements of the fish, such as the activity level and how much waste they produce, then going from their. Much safer. I've also heard one gallon per square inch, but I'm no mathmetician so I don't let their calculations confuse me. :p Just stick with the needs of the fish, don't y'all think? :)

It is all on how the look of the tank is. If it looks full then it is, if it looks empty then it is. I have thought long and hard about this rule and I find it is a simple myth adapted by beginner aquarists. I say add one or two fish at a time and you will know when your tank is full, trust me it is instinct.