Stocking

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

Total length of fishLight stockingRecommended
100% level stocking
Heavy stocking*
1inch / 2,5cm1816301890
2inch / 5cm2893280
3inch / 7,6cm103297
4inch / 10cm51750
5inch / 12,7cm31133
6inch / 15,3cm3927
8inch / 20,3cm1411
10inch / 25,4cm126
12inch / 30cm013
* ONLY with very heavy filtration
Labidochromis caeruleus – Yellow Lab
Labidochromis caeruleus – Yellow Lab

For a 50 gallon tank the stocking numbers are:

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

Total length of fishLight stockingRecommended
100% level stocking
Heavy stocking*
1inch / 2,5cm90315945
2inch / 5cm1447140
3inch / 7,6cm51648
4inch / 10cm2825
5inch / 12,7cm1516
6inch / 15,3cm1413
8inch / 20,3cm025
10inch / 25,4cm013
12inch / 30cm001
* ONLY with very heavy filtration
Metriaclima zebra OB
Metriaclima zebra OB

For a 25 gallon the stocking numbers are:

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

Total length of fishLight stockingRecommended
100% level stocking
Heavy stocking*
1inch / 2,5cm45159492
2inch / 5cm62390
3inch / 7,6cm2824
4inch / 10cm1412
5inch / 12,7cm038
6inch / 15,3cm027
8inch / 20,3cm013
10inch / 25,4cm001
* ONLY with very heavy filtration
Neocaridina davidi – Blue Shrimp
Neocaridina davidi – Blue Shrimp

For a ten gallon the numbers are:

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

Total length of fishLight stockingRecommended
100% level stocking
Heavy stocking*
1inch / 2,5cm1863189
2inch / 5cm3928
3inch / 7,6cm139
4inch / 10cm015
5inch / 12,7cm013
6inch / 15,3cm012
8inch / 20,3cm001
* ONLY with very heavy filtration
Metriaclima Red Zebra
Metriaclima Red Zebra

For a five gallon the numbers are:

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

Total length of fishLight stockingRecommended
100% level stocking
Heavy stocking*
1inch / 2,5cm93190
2inch / 5cm1414
3inch / 7,6cm014
4inch / 10cm012
* ONLY with very heavy filtration

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.

Nimbochromis fuscotaeniatus
Nimbochromis fuscotaeniatus

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.

Nimbochromis venustus
Nimbochromis venustus

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.

Andinocara rivalatus – Golden Saum
Andinocara rivalatus – Golden Saum

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

Cyrtocara moorii – Blue Dolphin Cichlid
Cyrtocara moorii – Blue Dolphin Cichlid

Translated in Dutch by Joost Abrahams
Proofread by John de Lange


Startpage Aquariumscience

Source: Aquariumscience.org – David Bogert

Bijgewerkt op 23 July 2023 door John

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