Stocking Quantities

[Helen G]

Had a few slightly conflicting pieces of information given to me recently and would like to clear it up.

1 inch of fish to 1 US gallon of water

OR

1 cm of fish to 1 litre of water

Now I know maths isn't my strongest point, but even I can see there is a bit of a difference here. ( A whole 6 inches in my case!)


Could someone please advise as to what is correct.

 

[dthoffsett]

It's 1" per US gallon, however, that's only a basic guidline as there are many factors to determine stocking, such as temperment, bio-load, territory needs, dietary needs, etc. It usually applies to slim-bodied community fish under 3 inches.

 

[OldMan47]

The whole rule is a way to keep new fish keepers from overstocking their tanks too much before they learn to look at a tank and say to themselves "That's enough for now".
There is no magic formula to follow but the inch per gallon will help keep you from overstocking if you only have small, one to two inches, fish. As soon as you get larger fish, it starts to fall apart fast and in the wrong way. A 10 inch fish cannot be kept alone in a 10 gallon tank but a fish like an endler with a light biological load on the tank can be kept at as much as 2 inches of fish per gallon or even maybe a litttle more. I currently am keeping about 40 endlers in a 20 gallon and its fine for them. They present a very light bioload per fish so my water stays good for them at that stocking level.
Your best bet in the long run is to start noticing how much fish food you need to keep your fish healthy and growing. You can start to think of fish food representing bioload since it is the source of that material. Once you get a feel for it, the amont that fish eat can guide you somewhat. Another thread I have read that sort of makes sense is to relate the volume of a fish's body to the bioload it will present to your tank. A longer fish is not just longer, it is often also wider and taller so the load goes up exponentially as the length of the fish goes up. This concept will probably keep you from getting into too much trouble using the inch per gallon rule. At 3 inches it might make you more likely to treat the fish as if it were 4 or 5 inches in the rule and thus prevent you overstocking because you used the calculation on larger fish.
In any size tank with fish of any size, if the tank is starting to look quite full of movement it is probably overstocked or close to it. This is the easiest rule to use and can help keep you out of trouble.