Some Plants Can Kill Shrimp. Myth or Not.

There are tons of articles about the best plants for a shrimp or fish aquarium. Actually, I wrote one myself. But is there another side of the coin? Are all plants good and useful for our shrimp? Can some of them be dangerous? Is it possible to take precautions? What should we know about the “dark side” of the plants?

Once I asked these questions myself, I expected to find plenty of information about it on the Internet. To my surprise, I did not find any article about this subject! Has anybody studied it? 

How so!? I have read and heard about multiple cases when shrimp have died after pruning plants or planting new plants. If those plants were clean or had already gone through quarantine what happened then?  So, I decided to do more research. Eventually, I managed to find pieces of information here and there. Thus, I decided to systemize everything I found and share it with you.

Poisonous plants in a shrimp tank?

I would like to start off by saying that, by all means, I am not a biologist and do not have any specific education about plants. Due to this fact, I have to refer to different studies, experiments, and experiences of professional shrimp breeders. I do not want to make any allegations in the first place.

Occasionally questions about poisonous plants like Elodea, Anubias, Cryptocoryne, etc., arise on shrimp forums. People complain about losing shrimp after pruning these plants. At first, I became cautious and made a list of potential “culprits.” Nevertheless, before calling them guilty I needed some proof. Therefore, I started my own research.

As I mentioned before, unfortunately, I could not find specific researches on how plants (and what type) can have a negative effect on shrimp. So, I decided to dig deeper and I found some interesting things which can be useful to all of us.

For example, I found the experiment describing the toxic effect of Elodea on Daphnia pulex*. (*The evaluation of ecotoxicological properties of Elodea Canadensis sap on Darphinia Pulex. By  Dr. Maria Aniskinа, Associate Professor, Department of Ecology of Syktyvkar State University, Russia, and Kirill Vagonov Eco-Biological Center, Russia and Peters P.H., with reference to De Bernardi R. Daphnia // Mem. Ist. Ital. Idrobiol. 1987. — p. 502).

I will put here some parts of that report (my translation).

“…In many sources of literature, it indicates (without confirming this fact) that the toxicity of Elodea canadensis juice can slow down the growth of fish and exert a lethal effect on the fry… To confirm or disprove the toxicity of the juice of the plant Elodea canadensis, we conducted a study that revealed the ecotoxicological properties of Elodea canadensis juice on aquatic organisms…

The purpose of this work is to study the effects of different concentrations of Elodea canadensis juice on the model organism Daphnia pulex… Daphnia pulex is a species of crustaceans of the Daphnid family… Females are 3 to 4 mm long, males are 1 to 1.5 mm…The species live in ponds and in the coastal zone of large reservoirs… Three concentrations of Elodea canadensis juice were selected – 9%, 23%, 33%. The juice concentration was obtained by extracting the juice from plants and mixing it in certain proportions with water.

Each concentration was tested 10 times with 20 experimental models of Darphinia Pulex  (overall 600 Daphnia pulex were involved in the experiments). The time of death of half of the control group, i.e. 10 individuals of D. pulex, was calculated, and thus the LD50 was detected for each concentration.

At the end of the experiment, we analyzed the data. The results were used to calculate the average death time of half the control group (LD50) organisms in each medium with a certain concentration.

For a concentration of 9%, the LD50 was 32 minutes, for 23% – 23 minutes, for 33% – 15 minutes…

Thus, as a result of the study, we can conclude that Elodea canadensis juice has high toxicity for D. pulex, which is clearly expressed through a direct relationship between juice concentration and mortality.”

My comment on this conclusion

Of course, the main goal of that research was fish safety. Nonetheless, it is a well-known fact that fish are more tolerant and hardier than our shrimp. Therefore, if this toxicity is deadly for the fish, it will wipe the shrimp colony as well.

Anyway, it is highly unlikely that any of us can add 9% of the Elodea juice. I will repeat, to get a lethal concentration of juice in a 100-liter aquarium (22 gallons) in 32 minutes, you need to add 9 liters (2 gallons!) of Elodea juice.

In my opinion, it is absolutely unreal to get that much juice in a home aquarium. Even to get 1 liter (0,25 gallon) looks incredible. This conclusion coincides with the experience of the professional shrimp breeder Robert Lupton “Flip Aquatics” when he was talking about Anubias plants.

Nonetheless, when it comes to weak shrimp or shrimplet, combining with God knows what else some of us have in our tanks, I can presume that in some rare cases the small concentration of toxins (after pruning) can potentially create a butterfly effect.

Since such concentrations of plant juices in aquarium conditions are not very likely, there is another explanation.

The Alternative explanation of the poison effect

There are about 20 nutrients required for plant health. Three main elements are nitrogen, phosphorus, and potassium (N, P, K) are required in abundance. They must be readily available through soil medium or fertilizer. The secondary elements are sulfur, calcium, and magnesium (S, Ca, Mg). The quantities required are much less than the macro elements, but they are needed in reasonably large quantities as well.

The content of chemical elements in plant tissues can exceed their concentration in aquarium water by a hundred (!) times. This shows the ability of plants to accumulate various substances, primarily phosphorus, potassium, and nitrogen, as well as organic compounds.

Examples

“The accumulation of Ni, Pb, and Zn in plants was determined and their effects on physiological parameters (chlorophyll aconcentration and degradation, lipid peroxidation measured as malondialdehyde) were evaluated in the leaves for both species. M. aquaticum showed a higher accumulation capacity of Pb and Zn than E. densa, particularly at the highest concentrations of exposure to these metals.” (“Nickel, lead and zinc accumulation and performance in relation to their use in phytoremediation of macrophytes Myriophyllum aquaticum and Egeria densa” Carlos A.HarguinteguyaM. LuisaPignataaAliciaFernández-Cirellib; F.L. Fu, Q. Wang Removal of heavy metal ions from wastewaters: a review J. Environ. Manage., 92 (2011), pp. 407-418)

For example, “submerged plants accumulate on average 50 g of nitrogen, 3 g of phosphorus and 45 g of potassium per 1 kg of dry mass. After decomposition, dead plants return some of the accumulated nutrients to the water finishing the cycle.”* (“Possibility of using aquatic plants for cleaning wastewater.” Professor E.M. Zainutdinova Ufa State University).

In practice, this means that if for any reason, the water in the aquarium contains heavy metals or some other pollutants, the plants actively absorb and accumulate these substances. After a while, their concentration in the plant can be significantly higher than in the water. When the plant is pruned, some of the previously accumulated substances are released into the water. In this case, aquarium tests may not detect exactly what kind of substances got into the water.

Notes:

1. Nonetheless, research says about kilograms of plants! I wonder who cut that much plants in the home aquarium?
2. A positive aspect of that research is that if the aquarium water was not contaminated, (for example, RO water was used) or changed regularly, then the plants do not accumulate that many bad substances due to their absence or insignificant presence. This means when you cut such plants, it releases only its juice into the water. And, as we already know, it is really difficult to achieve a lethal concentration of juice in aquarium conditions by itself.

Shrimp Tank vs Heavily Planted Tank

We all know that plants are super beneficial for shrimp tanks. There are a huge number of undemanding species of plants, which help to keep the proper water parameters. They provide the tank with lots of surface area and give shelter and protection to our shrimp and shrimplets.  Nonetheless, we should not forget what our priorities are.

The point is that a heavily planted tank with fast-growing plants can have unfavorable effects on the microorganism fauna in the tank, on which the shrimp feed. Fast-growing plants compete very efficiently with the types of algae, biofilm, and other microorganisms that usually grow in the tank and form a very important part of the shrimp diet. So the more rapidly you see plants are growing, then the more nutrients they are going to pull out of your water.

The plants take away the nutrients necessary for microorganisms to survive and thrive.  When it happens the shrimp stop grazing on the plant leaves because there are no food-organisms growing on the leaves.

The heavily planted tank can adversely affect the nitrifying bacteria in your aquarium by consuming their favorite food before the bacteria can, namely ammonia and nitrite. As a result,  in some time the majority of your nitrifying bacteria in a tank die off. This is a disaster waiting to happen *if* you decide to prune heavily.

Once you prune your plants, ammonia starts accumulating.  This ammonia usually occurs in trace amounts and is not always measurable.  All you will notice is that your shrimp will start dying one by one for “no” apparent reason. Hence, make sure that plants do not completely take over the tank and make sure that you only prune a little bit at a time.

The problem of a Heavily Planted Tank is very debatable and controversial.

There are people who completely disagree and those who have experienced the loss of population under similar circumstances. Also, there are some shrimp breeders who do not use any fertilizers. If we decide to go for a heavily planted and fertilized tank, be ready to have problems with water parameters over a long period of time.

Frankly saying, I tend to agree with that. In the long run, the fertilizers can accumulate in the water over time. Being a very sensitive invertebrate, it can negatively affect shrimp. Although, we do not have any scientific researches I am still very conservative about everything that can have an impact on the eco-system of the aquarium.

There is no need to risk the life of your shrimp colony just to have a little bit better and faster growth of the plants. Once again, remember your priorities.

Conclusion

The conclusion here will be very simple. Nobody knows for sure, but there are some evidence and suspicious coincidences that different plants can affect shrimp in our aquariums. So, if you want to be on the safe side:

• Do systematic water changes.
• Do not overplant your aquarium.
• Use slow-growing plants (like Anubis or Java Fern). They are safer for shrimp keeping.
• Whenever it is possible, cut and prune plants with potential toxic juice outside of the tank.