How Many Shrimp Can I Have in My Tank?

How many shrimp can I have in my tank is, probably, one of the most common questions in the hobby? The question is pretty simple but it also has some factors to consider for calculating safe stocking levels. Instead of using a rule of thumb method, I will be talking about the scientific approach!

According to the study, keeping about 5 – 10 dwarf shrimp per gallon (around 4 liters) is considered to be the optimal shrimp density, with respect to growth performance. The results of the experiments showed that the increase in shrimp density reduced the final weight and size of the shrimp.

If you got curious and want to know more about shrimp density, this article will answer all of your questions in detail.

How Density Affects Dwarf Shrimp Growth

As I have already said lots of aquarists want to know how many dwarf shrimp they can keep in 5, 10, 20-gallon tanks.

Luckily, a few years ago this question was answered by scientists. In their experiments, they tested how density affects the size, survival, and breeding rate of dwarf shrimp (Neocaridina sp.).

To exclude any variations, water parameters and feeding ration were the same for all groups of the shrimp. Scientists divided dwarf shrimp into 3 main groups:

Small groups, 2.5 shrimp per 1 liter (about 10 shrimp per gallon).
Medium groups, 5 shrimp per 1 liter, (about 20 shrimp per gallon).
Large groups, 10 shrimp per 1 liter (about 40 shrimp per gallon).

The experiments continued for 90 days and these were the results:

Shrimp from small density groups weighed 15% more than shrimp from the medium density groups.
Shrimp from medium-density groups weighted up to 30-35% more than shrimp from the large density groups.

By the end of the experiment, it was obvious that small density groups (10 shrimp per gallon) showed the best growth results and gained more weight.

How Density Affects Survival Rate of the Shrimp

Dwarf shrimp are social animals. They do really well in the company of their own kind. Even more, in large groups, they become more outgoing and confident. As a result, the larger the group, the better their displays will be.

Another great news is that even high shrimp density in the tanks will not affect much their survival rate. Results of the experiments showed the survival rate of different groups:

Small density group – 92%,
Medium density groups – 93%,
Large density groups – 87%.

As we can see, the survival rate results in shrimp are consistent within the statistical error.

It means that we can safely conclude that density has little to no effect on dwarf shrimp in the tank.

How Density Affects Breeding Rate of the Shrimp

According to multiple studies, larger females usually produce more eggs per clutch in crustaceans than smaller ones.

This pattern applies to dwarf shrimp as well. At the lower density, we can also register an increased reproductive frequency in females.

Note: Generally, a female shrimp can produce 21-51 babies per hatching.

Therefore, density indirectly affects the breeding rate of the shrimp because, in small density groups, females can grow faster and larger. As a result, they can carry more eggs and produce more baby shrimp.

Even though, the difference in egg numbers may not be that big at first. Eventually, in the long run, it will become pretty considerable.

Important Factors of Shrimp Stock Density

Now, when we know that the optimal shrimp density is 10 dwarf shrimp per gallon (about 4 liters), how can we apply it to our tanks in reality?

Let’s be honest, nobody in their right mind would count shrimp to keep the perfect ratio all the time.

Of course, it can be easily done in small tanks. But what about big ones? For example, how can we count 200 shrimp in a 20-gallon tank? It is absolutely not possible!

Therefore, all these optimal numbers are necessary only for professional breeders, it helps them to be more efficient.

Other people do not really need it. If you are an ordinary aquarist and your shrimp colony starts growing, it is a sign that your shrimp are happy and healthy. Therefore, all these numbers become irrelevant to you in most cases.

When aquarists ask about shrimp density and tank size, they often apply standards for fish to shrimp. This is wrong and they should not do that.

Unlike aquarium fishes, dwarf shrimp do not become more aggressive in reduced environments.
Dwarf shrimp do not produce a lot of waste. Therefore, there will not be a significant deteriorating water quality because of this.

Even more, it is not only about mathematic. You can have the optimum shrimp density but in reality, they may suffer. Why?

Because density and size of the tank are only one of the factors!

In the aquarium hobby, the determining factor is how well you can maintain the tank.

For example, the temperature is another factor that can affect density.

Density and Temperature in Shrimp Tanks

A freshwater aquarium at 77 °F (25 C) should hold about 8.3mg/l of dissolved oxygen.

Overstocking and higher temperatures will lead to the depletion of oxygen levels in an aquarium.

In addition, low levels of aeration in shrimp tanks can easily cause ammonia build-up to reach toxic levels it will also affect shrimp

Density and Different types of Aquarium Shrimp

In the aquarium hobby, there are lots of different types of freshwater shrimp. They come in all shapes, colors, and sizes.

Neocaridina and Caridina species are very small (up to 1 inch or 2.5 cm) and can be kept in big numbers but what about other shrimp?

Opae Ula Shrimp (Halocaridina rubra) is the smallest shrimp (1.5 cm or 0.5 inches). There is no recommended density. A 5-gallon tank will suit all their needs. These shrimp can live up to 20 years and have an extremely slow metabolism.
Amano Shrimp (Caridina multidentata) and Ghost shrimp (Palaemonetes paludosus) can grow up to 2 inches (5 cm). Recommended density – 1 shrimp per at least 1 gallon.
Whisker shrimp – adult size 2 inches (5 cm). Recommended density – 1 Whisker shrimp per at least 1 gallon.
Bamboo shrimp (Atyopsis moluccensis) may reach 3 – 4 inches (8 – 10 cm). Recommended density – 1 Bamboo shrimp per 10 gallons.
Vampire shrimp (Atya gabonensis) is one of the biggest pet shrimp, they can attain an impressive 5 – 6 inches (12 – 15 cm). Recommended density – 1 Vampire shrimp per 15 gallons.

Can I keep just one shrimp?

Well, technically, it is possible. However, I would not recommend it. Lonely, dwarf shrimp will be under constant stress because they are social animals that require company. As a result, it will affect its wellbeing and behavior, for example, it will hide most of the time.