Today we are going to talk about another unwelcome parasite in our shrimp aquariums – Freshwater Hydras. Shrimp breeders (as well as fish keepers) consider them to be pests which can cause problems and they are absolutely right.
Hydras are named after the nine-headed sea snake of Greek mythology which re-grew heads after decapitation. Luckily, we have ways to deal with it without chopping off its heads. No Planaria, Hydrogen peroxide, Fenbendazole and etc. can easily remove it from our aquariums. Nonetheless, we need to know more about this parasite to protect our shrimp.
Hydra is a small-sized polyp from the same phylum (Cnidaria) as sea anemones and jellyfish. While most cnidarians are marine, Hydra is unusual in that it lives exclusively in freshwater.
It was first described by Antoni van Leeuwenhoek (1632–1723) in a letter he sent to the Royal Society on Christmas day, 1702. These creatures have long fascinated biologists due to their ability to regenerate from small pieces.
Remarkably, even cells from a mechanically separated Hydra can restore, and over the course of about a week reassemble into a functioning animal. How this process occurs scientists still do not understand completely.
Types of Aquarium Hydra
Several species of hydra have been recorded, but most are difficult to identify without detailed microscopy. Two species, however, are distinctive. They are the most common in our aquariums.
- Hydra (Chlorohydra) viridissima (Green hydras) is a bright green species, owing to the presence of numerous algae called zoochlorellae, which live as symbionts within the endodermal cells.
They are more commonly whitish in color, actually. The green algae carry out photosynthesis and produce sugars that are used by the hydra. In return, the carnivorous diet of the hydra provides a source of nitrogen for the algae.
Green hydra are small, seldom more than 0.4 inches (10 mm) long, with tentacles about half the length of the column.
- Hydra oligactis (Brown hydras) is easily distinguished from another hydra by its very long tentacles, which may extend to 2 inches (5 cm) or more when relaxed.
The column is a pale translucent brown, 0.6 to 1 inch (15 to 25 mm) in length, with the base distinctly narrowed to form a “stem” or “foot.”
Body Structure of Hydra
Their combined mouth–anus (gastrovascular cavity) structure is ringed with outwardly projecting tentacles containing stinging cells (nematocysts). This means they only have one opening in their body and that is a mouth but that also serves to get rid of waste products.
Interesting fact: Hydra has the tissue, but it lacks organs. It consists of a tube about 5 mm long formed by two epithelial layers (endoderm and ectoderm). It has a head consisting of a mouth surrounded by a ring of tentacles at one end and an adherent disk, the foot, at the other end. Interspersed between the cells of the epithelial layers are multipotent stem cells that give rise to four differentiated cell types: gametes, nerves, secretory cells, and nematocytes — the stinging cells that define the phylum Cnidaria.
Also, due to the structure, they have the ability to regulate their water inside their bodies. So they can elongate or contract their bodies at any time.
Although it lacks sensory organs, Hydra is responsive to light.
Reproduction of Hydra in Aquariums
Hydra undergoes two mutually exclusive modes of reproduction: at warm temperatures (18–22°C or 66-72F) they reproduce asexually by budding. (Spermatogenesis in Hydra oligactis: II. How temperature controls the reciprocity of sexual and asexual reproduction. Developmental Biology Volume 146, Issue 2, August 1991, Pages 292-300).
Reproduction in hydras typically takes place asexually by a process known as “budding”. A bud-like growth on the body of the “parent” hydra eventually grows into a new individual that becomes separated from the parent.
When conditions are harsh, or there is a shortage of food, hydras can reproduce sexually. A single individual may produce both male and female sex cells, which are released into the water where fertilization occurs.
The egg develops into a larva, which is covered in tiny hair-like structures known as cilia. The larva may either settle immediately and develop into a hydra or become surrounded in a tough outer layer that allows it to survive harsh conditions.
How Fast Hydra Reproduces
The answer is very fast! Under favorable conditions, (it is very unpretentious) the hydra is able to “generate” up to 15 small hydras a month. It means that every 2-3 days it makes its copy.
One hydra, in just 3 months, is capable of producing 4,000 new hydras (considering that “children” also bring 15 hydras a month).
Why Hydra is Dangerous to our Shrimp
In nature, hydra feeds on small aquatic invertebrates that are paralyzed by the stinging cells when the prey comes into contact with the tentacles. The prey is then brought to the mouth by the tentacles and taken into the body of the hydra.
Some of their favorite foods include organisms up to twice their size like Daphnia, Cyclops, and other freshwater copepods.
For example, Daphnia, (small planktonic crustaceans) are 0.2–5 millimeters (0.01–0.20 inches) in length. I have already covered the breeding and life cycle of shrimp in another article and it takes 14 days for the baby shrimp to reach 5,4mm in length. Meaning that hydra can easily catch 14 days old baby shrimp! I would say that any shrimplet less than 1-month-old will be in mortal danger if there are hydras in the tank.
Hydra paralyzes the prey with neurotoxins which it releases from tiny stinging organelles, called cnidae or nematocysts. The cnidae is a part of the ectodermal cells of the column, especially the tentacles, where they are packed in high densities.
Each cnida is a capsule containing a long and hollow thread. When stimulated by chemical or mechanical signals, the permeability of the cnida increases. The largest cnidae (penetrants) contain the neurotoxins that hydra injects into prey via the hollow thread.
Smaller cnidae, which are adhesive, coil spontaneously on contact with prey. It takes less than 0,3s to sting the prey.
As a result, when the shrimp comes too close to Hydra, you will notice how they jerk away very quickly. The same happens with a small fish or fry, they swim away very abruptly. The reason is that hydra will “stab” what they think might be a potential predator or prey.
If shrimp are full-grown it does not tend to bother that much. Nonetheless, if you have got a newly born shrimp it can harm or even kill and eat them depending on the size.
Note: Stings from a few hydras are harmless to most people. Nevertheless, if we are talking about thousands and millions it can damage even human skin. For example, on fishing nets left submerged for a long time, the combined stings have been known to cause rashes on the hands of fishermen!
|Treatment length||Up to 1 week|
How Hydra Eats
Hydras are predatory and voracious. They eat worms, insect larvae, small crustaceans, larval fish, and other invertebrates, such as Daphnia and Cyclops.
Hydra is not an active hunter. They are classic ambush predators that sit and wait for prey to come close enough to strike. The instant prey is close enough to activate a reaction of stinging cells.
It is an instinctive response. Then the tentacles start to curl around and close on the victim, drawing it to the mouth at the base of the stalk of tentacles.
If it is small enough, hydra will eat it. If it is too large to consume it will be discarded, possibly to be found by a mystified aquarist, with no obvious cause of death to be seen. In case there is not enough prey, they can get some amount of food by absorbing organic molecules directly across the surface of their body.
When there is no food at all, hydra stops reproducing and starts using their own tissues for energy. As a result, it will shrink to a very small size before it finally dies.
How can Hydra get into Shrimp Aquarium
Hitchhiking with new plants (quarantine the plants), wood, or rocks harvested from outdoor water sources. They can sneak into your tank as snails do. It is almost impossible to notice them. Especially, when they retract their tentacles they look like a floating piece of sand or a bit of floating debris.
How to Recognize Hydra in Time
- By the look
Frankly saying it is very hard to notice them in the beginning. At first, they are small and appear initially as little white spots. Then they become like kind of little white stringy things.
Anyway, that is not enough to discern what they are. Unless you are ready to sit 24/7 with a magnifying glass near your aquarium.
Once they start clinging to the glass or a black surface, it will be easy. Their “strange” form will catch your attention. Unfortunately, in most cases, it means that hydras have already spread in your tank. They multiply very fast!
- By the movement
Hydras are generally sessile, but they can detach and move to another location by gliding slowly on their base. They move very oddly. Hydra cannot swim like fish or shrimp.
They can either suddenly move by flexing their tentacles or they can kind of somersault. Their movement mimics that of small worms when they do this.
How to Remove Hydra From the Shrimp Tank
Actually, I would like to start off by saying how not to remove them.
Do not squash it with your nail! Remember that they can regenerate themselves. In some ways, Hydra is, for lack of a better term, immortal. Yes, you have heard me right.
Researchers have discovered a set of transcription factors that control the ability of the Hydra to constantly renew all of its cell types ultimately preventing the effects of aging.
Daniel Martinez followed 100 adult Hydra for four years, discarding the buds as they were produced. The parental animals did not undergo age-related changes. Individual cells die in Hydra, but the organism as a whole does not have a fixed lifespan. (Current biology. Quick guide Hydra. Kristine M.GlauberCatherine E.DanaRobert E.Steele. Volume 20, Issue 22, 23 November 2010, Pages R964-R965).
So damaging them is simply counterproductive.
If it is a small infestation you can try to physically remove it. Really the best way to kill them is to grab them and to just physically remove them from your tank. You can also siphon out any Hydra you see. If there are not too many, simply take some care not to damage them while you do so.
Reduce feeding sources
Hydra is a predator. They only eat living things that they kill with their poison. Overfeeding often increases the populations of tiny prey hydra do feed on. Therefore, it would be better to avoid overfeeding, which is a very common mistake with many shrimp breeders. Use feeding dishes for food control.
You can try to starve hydra out. Like most other pests, Hydra can only gain a foothold if they have access to food. Cutting back food and doing target feedings can keep Hydra controlled. That is the long-term solution (at least a few weeks), and it will work.
Hydra themselves are food, for any fish that are willing to eat them. There are reports that Sparkling gouramis, Blue gouramis and etc. will eat Hydra. The problem is that fish is the problem itself for the shrimp tank. Even small fish can wipe the shrimp colony. In my opinion, it is not worth the risk in our case.
There are some snails species that have been reported to eat Hydra, for example:
However, do not think that these snails will specifically hunt down the Hydras. No, it is just they do not care what to eat. Unfortunately, these snails (especially Marisa cornuarietis) can also eat some plants. So, be careful, and do your research beforehand.
The other important thing that most freshwater snails benefit the aquarium is by consuming waste products. Because they are consuming waste products less waste is available for small microscopic organisms that may be a food source for the Hydra.
High and low Temperature
You can try to use a heater to kill the hydra. In this case, you will have to remove all your shrimp and fish from the aquarium if you do not want to kill them all. After that, raise the temperature to 105 – 110 degrees Fahrenheit (41-43 C) for several hours.
Most plants should survive this treatment. It is not a long time and should not be enough heat to harm most of them. However, if you have any very sensitive or very highly valued plants, I would take them out and place them into separate containers of water.
Another way is to put it in very cold water. Unfortunately, it can go dormant oftentimes rather than die.
Hydra is responsive to light that is why you can see a lot of them on the front glass of the aquariums. Use it against them. You need to:
1. Shade your aquarium or turn off the light completely.
2. Add another piece of glass to the glass from the inside of the aquarium.
3. Use the flashlight or any other source of light so the light will go through these 2 layers of glass.
4. Wait a few hours.
5. By the end of the day, the hydras will move to the light and sit on this piece of glass.
6. Carefully remove the second glass with the hydra on it.
This method will not remove all hydras. Nonetheless, it can reduce the number significantly. It is better to combine it with other methods.
Medication against Hydra
Hydrogen peroxide (H2O2)
Hydrogen peroxide (link to check the price on Amazon) (H2O2) is an oxidizing agent and is often used to kill bacteria on a cut or wound.
When applied, the enzymes present in cells act as a catalyst and H2O2 starts breaking into water and oxygen atoms, which badly need second electrons. With the electrons being stolen, the cell wall gets damaged and the bacterium dies. This is also how it kills Hydra.
Warning: DO NOT overdose. Check and double-check your calculations. Overdosing can kill your shrimp.
I have found that the safe level is 14.3 μl H2O2/L, approximately 50 % of the largest applied dose that caused no mortality (NOAEC), which was 29 lL H2O2/L. (“Short communication: Acute toxicity of hydrogen peroxide in juvenile white shrimp Litopenaeus vannamei reared in biofloc technology systems” Plinio S. Furtado, Fabiane P. Serra, Luis H. Poersch, Wilson Wasielesky Jr. Aquacult Int (2014) Received: 6 March 2013)
Measure the water volume of your aquarium. Take into consideration (approximately) substrate, decorations, etc.
- Turn off your filter
- Use 3% Hydrogen peroxide at 1.5ml per gallon or per 4.5 liters.
- Evenly spread H2O2 across the surface of the aquarium.
- Gently stir the water to spread it.
- Wait for 60 minutes
- Turn your filters back on.
- The same week do a water change and add your favorite bacterial supplement back to the tank.
Note: besides killing hydra it will give your tank a fresh start but with a filter that is already cycled! Unfortunately, you can lose some biofilm but it will not disrupt the cycle anyway. Even more, if you use a bacterial supplement it will grow back very quickly.
Sea salt or Iodine-free table salt
“Also, sea salt or iodine-free table salt is supposed to destroy the Hydra. Therefore, you can give 20g on 100 liters of aquarium water. It is not dangerous for plants and shrimps according to the statement of shrimp holders. Even in higher proportioning above a few hours”. I have taken it from the German professional site about shrimp.
No-planaria, Planaria Zero, Canine Dewormer safe-guard, and Panacur
You can see the dosages and read more about “Planaria and Shrimps. How to remove them” right here. There is detailed information about it.
There is no reason to panic if you have found a hydra in the aquarium. They will not annihilate your shrimp colony in the blink of an eye. However, it would be better to make preparations to deal with the Hydra as soon as it is possible. So as to reduce any potential losses.
|Read also my article “Understanding Dwarf Shrimp Diseases and Parasites”.|