13. Stocking

If one is new to fishkeeping, stocking is best looked at not by numbers but rather by water clarity. Slowly add some fish. Then see how it goes. Keep looking down the length of the tank and judging how clear the water is. If the water looks even a little bit cloudy do not add any more fish till the cloudiness clears up. Don’t worry about numbers. Gage the stocking by the health of the tank. How clear is the water? When the water is clear, add more fish. Cloudy water? Wait a while, till the cloudiness or “dullness” clears. Then you can add more fish. Simple!

Stocking and Opinions

The topic of stocking is largely OPINIONS, not experimentally derived scientific facts. Let me repeat that:

The Topic of Stocking is Largely OPINIONS

So do what YOU want to do with YOUR aquarium. If you want some guidelines which are largely just my opinions, read on.

The Science

Note that there is some science here. And the science says that VERY VERY HEAVY stocking of aquarium tropical fish is quite healthy and does little harm to tropical aquarium fish. The science is based on university research on the zebrafish and can be found in the following article:

13.2. Calculating Stocking Ratio

My Opinions and Recommendations

IN MY OPINION, the following stocking ratios, based on the volume of fish, are perfectly acceptable for a 100 gallon tank:

Number of fish for stocking in a 100 gallon or 378,54 liters aquarium

For a 50 gallon tank the stocking numbers are:

Number of fish for stocking in a 50 gallon or 190 liters aquarium

For a 25 gallon the stocking numbers are:

Number of fish for stocking in a 25-gallon or 95 liters aquarium

For a ten gallon the numbers are:

Number of fish for stocking in a 10 gallon or 37,85 liters aquarium

For a five gallon the numbers are:

Number of fish for stocking in a 5 gallon or 18,93 liters liters aquarium

Look out with the heavy stocking columns for the ten and five-gallon aquariums. The filters for small tanks are always very small cartridge or air-operated sponge filters. These filters are just totally inadequate to support heavy stocking. So small aquariums should not be heavily stocked. If one puts something like a very small canister filter on a ten-gallon, one can think about heavy stocking. But I’ve never seen that done.

To get a good number with mixed sizes just takes some common sense approximating. Start with the largest fish and work your way down in size. Say you have a 50 gallon (189 liter) and want to stock at the maximum recommended level.

Say you want 10 three-inch fish. The 10 three-inch (7,5 cm) fish is very roughly about half the quotas for “Maximum recommended”. That leaves 50% which could be 23 two-inch (5 cm) fish (50% of 47). But lets say its ten three-inch (7,5 cm) (roughly 50%) and 12 two-inch (5 cm) (roughly 25% of 47). Then you would have room for one fourth (25%) of the 315 in one-inch (2,5 cm) fish or about 80 one-inch fish.

So it is 10 three-inch (7,5 cm), 12 two-inch (5 cm) and 80 one-inch (2,5 cm) fish in a fifty-gallon (189 liter).

That is all very rough. A more thorough analysis involves using the weight of the fish and gets all complicated totally unnecessarily. The easy way to do it is just to add small numbers of fish till the water turns “dull”. Then stop adding till the water becomes crystal clear. Then add more fish. Easy.

Now these numbers, especially the “heavy stocking” numbers, will absolutely send some “fish police” into absolute hysteria and get this site kicked off many Facebook forums. Remember, the heavy stocking levels are only “ MY OPINIONS” (not “rules”) based on WELL FILTERED AQUARIUMS WHICH HAVE LARGE FILTERS WITH GOOD MEDIA THAT HASN’T BEEN FREQUENTLY CLEANED!!!!!

There are ways to determine the amount of media and the amount of filtration needed for a given loading of fish. They can be found in the following link:

8.8. Sizing Filters and Media

In the in-depth articles below I give my OPINIONS on the topic and the OPINIONS of others. It is all a rambling set of OPINIONS so unless you want to get really bored, stop right here.

Stocking in Greater Depth

Hopefully, the following links can put some common sense into this subject:

13.1. Stocking Opinions

13.2. Calculating Stocking Ratio

13.3. Lifespan of the Fish

And the common or narrow-bodied goldfish should be stocked as a five-inch fish.

This is delved into in this link:

17.5. Goldfish

Translated in Dutch by Joost Abrahams
Proofread by John de Lange

Startpage Aquariumscience

Source: Aquariumscience.org – David Bogert