The crayfish are just very beautiful crustacean that belong to the families Astacoidea and Parastacoidea. We usually find them in rivers, especially in those where unscrupulous people haven´t been yet.
Most of these creatures are quite striking, and since they are more accessible than sea crabs, they are often used as pets in many occasions, to decorate the different fish tanks and aquariums around the world.
Thanks to the publicity that has been made of them by different television programs, there are many people who acquire these beautiful little crabs, in spite it isn´t always a good practice and sometimes they just don´t recognize it
Table Of Content
- 1 Main Characteristics of the Crayfish
- 2 What is the Crayfish´s size
- 3 Crayfish´s Anatomic Features
- 4 Crayfish´s Common Habitats
- 5 Crayfish´s Distribution
- 6 Crayfish in Fish Tanks
- 7 Crayfish´s Reproductive Method
- 8 Funny Facts About The Crayfish Reproduction
- 9 Crayfish´s Care
Main Characteristics of the Crayfish
These creatures are decapod river crabs crustaceans, which breathe by employing gills very similar to the feathers of birds. The body of most river crabs is divided into nineteen parts, which in turn make up the cephalothorax and abdomen.
The head and the thorax are located on the frontal portion of the body, and they are divided by the cervical groove. The face and eyes are located on the frontal portion of the shell, while the mouth is located in the ventral part of the head, surrounded by the legs that are shaped like pincers that the river crabs employ to feed. They also have a pair of antennas that make up their sensory organ of balance.
These crabs are also characterized by having an appendix on each part of their bodies, although in certain occasions, some crustaceans do not have it, or are limited. As these crabs usually live underwater, they use their gills to breathe. This is a kind of vascularized system where oxygen is absorbed by propagation into the blood, and carbon dioxide is transferred to water.
Their gills are located inside the thorax, at the beginning of the rear legs, and as we mentioned before, they resemble bird feathers, since they need to have a lot of surface to be able to absorb the oxygen of the water.
These crabs can live in waters that do not completely freeze, so they abound in rivers and streams, specifically in places where their predators can´t reach them. Only very few species of river crabs can, tolerate contaminated water.
What is the Crayfish´s size
These crustaceans are usually only seventeen centimeters long and like the rest of the arthropods, they also molt their exoskeleton.
Since they are decapods, they have five pairs of legs inserted on their belly, where the first of them correspond to two well-developed pincers which they employ to capture and manipulate their food. The next legs are also tweezers, but much smaller than the previous ones; and the last two strangely possess a nail.
Excluding the first pair of legs, where the crayfish have the largest pincers, the remaining ones are used for displacing purposes.
The females of the crayfish have their sexual orifice located in the third pair of locomotors legs, while in the males, their sexual orifices open in the basal parts of the last legs; and this is the sexual differentiation that exists between males and females of crayfish.
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Crayfish´s Anatomic Features
As we mentioned earlier, the body of these creatures is divided into several parts that we will describe below.
Abdomen: lower part of the body of the crab
Antenna: organ of perception of the crab
Antennule: small antenna.
Head: top of the crayfish.
Cheliped: anterior leg terminated by a mouth.
Endophyte: inner part of the uropod.
Exophodyte: external part of the uropod.
Compound eye: complex organ of the river crabs crab view.
Paw locomotive: member that allows him to walk
Face: guard of the crayfish cover binding
Segment: ring of the crab abdomen.
Telson: last segment of the abdomen
Thorax: upper part of the body of the crayfish.
Uropod: fin leg of the crayfish.
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Crayfish´s Common Habitats
The crayfish usually live not only in cool clear waters of fast currents, but also in more temperate waters, with slimy bottom, and of less current However, the middle and lower water courses, the river basins, and the headwaters of rivers and streams can also be inhabited by these crabs.
In general, these crustaceans prefer to live in shallow rivers plenty of vegetation. It is essential for them, the presence of oxygenated waters, banks of steep wall to be able to excavate their holes, and above all, it must contain enough stones and roots that allow them to take refuge from their predators.
The species of this group usually flee from the sunlight; and therefore, they tend to hide in holes dug in the sand and under the stones. As a consequence, they are mainly nocturnal creatures, who remain active from spring to autumn, hibernating the rest of the year in their favorite dens.
The crayfish usually prefer waters rich in calcium; with a temperature range between 10 and 20 Celsius degrees. And since they prefer fresh, clean and crystalline waters, this small animal is a natural indicator of the quality of the river environment.
Where there is a presence of river crabs; it can be guaranteed that the waters are free of impurities.
These crabs are distributed throughout the world, with the sole exception of the African continent. Of the five hundred species that exist in the world, only five of them are autochthonous of Europe. For this reason, this small crustacean is distributed in the center and south of this continent, including the western Mediterranean arch. They are also present in the British Island, France, Corsica, Belgium, Germany, Switzerland, South Australia, Bosnia, Croatia, and Italy. In the same way they are also distributed throughout the American continent, with especially in the tributaries that have less speed in the water flow. This is because these crabs prefer rivers that contain gravel bottoms, although they can also adapt other bottoms of variable nature.
Crayfish in Fish Tanks
In general, the fish that live in fish tanks are those are sold in shops, which come from breeding centers, which means that they were born in captivity, and not in the river. These have gone through a specialized sanitary supervision, so they are fit to live in a fish tank. It is not recommended to put river fish in a fish tank.
The rivers do not always have all the purity that we would like them to have, and this is because they may be close to a factory, or they may have an illegal dump, or they may be contaminated with garbage left by human beings on the shore; and all these possibilities can make the fish sick, producing malformations and parasites in them. How can you be sure if one of these specimens is not sick? It will be enough with only one sick fish that you enter into your tank, to finish the others in a few days.
When the crabs live in the rivers, they are accustomed to freedom, to provide themselves with their food, and to come and go as they prefer. If a crab is removed from its habitat to enclose it in a fish tank of very few proportions, it is likely that it will feel sad and die in a few days.
The first thing that must be taken into account is to offer a comfortable habitat for them. So, you should first of all have clean and clear water. For this reason, it is highly recommended, to have a filter installed in the fish tank, to keep the habitat of crabs as clean as possible.
The crayfishrequire places where they can hide to feel safe, so the fish tank must have stones, shells, wooden trunks, everything they can use to browse, climb, and dig, which are the common are habits of these creatures.
These crabs feel more comfortable when they are in the dark, so you must ensure that the environment is suitable for them. They also like to climb the plants and rocks, so it is necessary to place a few of them, as well as places where they can hide when they are molting their exoskeleton.
Crayfish´s Reproductive Method
Crabs have different ways to attract their couples, as it can be by employing pheromones, acoustic or vibratory media, and even visual means, such as the fiddler crab, which is one of the most boastful crabs in terms of courtship.
They carry out internal fertilization, and the copulation is performed belly to belly. This mating takes place just after the female has molted its exoskeleton, since such structure is softer at that moment which makes the process easier. Then the female stores the sperm for a certain time, before the eggs are fertilized.
Once the fertilization takes place, the ovules are located in the abdomen of the mother just below the tail, and thanks to a sticky material they remain fixed to it during all the embryonic development. At this time these eggs are called roe, because of their resemblance to round berries.
When the development is completed, the females release the larvae that have just hatched into the water, which then become part of the plankton. At this time, these are tiny larvae that, when floating, take advantage of the current of water.
The larvae are provided with a spine that reduces the predation of larger animals. Likewise, since they feed on the food provided by the yolk of the egg, they do not need to search for food during this stage, which also increases their life expectancy.
Since there are many species of crayfish, and therefore a great diversity, this process can vary between one species and another. For example, in the case of the blue river crab, the female keeps the eggs in her abdominal appendix, and makes burrows to protect her off springs, and to offer them a humid environment until they hatch.
Depending on the weight and size of the females, the crabs can produce about 200 juvenile eggs.
The reproduction of the river crabs is conditioned by the temperature of the water, and the duration of the day. For this reason, the mating of this specie usually happens when spring starts, depending also on where they are located. This is the right moment when the males are well developed to fecundate the females.
The Life Cycle of the Larvae
Each species of crabs goes through a certain number of stages, which are usually separated by various exoskeleton moults. Then they reach the stage called megalopa, where they are more like an adult crab, but with the difference that they have the abdomen protruding back. After another molt takes place, the specimen is considered as a minor crab and it no longer floats, but walks on the lower part of the river. It is essential that these first changes take place in their natural habitat, so that the crab has a better chance of survival. After overcoming this stage, the crabs are already juveniles, but they will still have to continue making changes until they become adults.
How the molt cycle is carried out
This cycle is determined by the hormones of the crabs. The molt takes place when the exoskeleton is already soft and partially eroded, then the new shell begins to appear. The crabs ingest large amounts of water, so that the old shell can expand to the point of cracking. This crack takes place along the rear edge of the carapace, where the crab begins to extract its entire body, including the lining of both the back, and the front of its digestive system. This requires an arduous work for the crab, in which it must invest many hours. This process must be done very carefully, because they could lose any part of their bodies, and if they get stuck in their old shell the will die. But once the molt has finished, they have a soft body that they can expand a little more so that they can develop comfortably. This is the proper moment for them to mate, but they must also take care, since because of the softness of their shells, they are also quite vulnerable to their predators. For this reason, they tend to remain hidden until their new shell hardens.
Funny Facts About The Crayfish Reproduction
According to the most recent studies, prostitution has been shown to exist not only in human beings, as we all know, but also among crabs!
The Researcher Patricia Backwell of the Australian National University said in a publication, that fiddler crabs understand sex as an exchangeable value. The fiddler crabs males differ from the females, due to their pincers which are considerably larger than the latter, which they use mostly for their protection. Then she observed the interested behavior of the females.
Such pincer is a powerful weapon for the male, since it allows him to defend himself from any enemy, which is something that females just can´t do. They are helpless and defenseless in the absence of this powerful pincer that males have. For this reason, the females exchange their sexual favors, for protection.
This researcher was able to verify by observing the sexual behavior of such crabs, that it is normal for females to choose males that are neighbors in their territory, to reproduce with them. In general, it is the males with the biggest pincers, the one who has more opportunities to mate with more females.
When entering a false attacker in the territory of the crabs, in 95% of cases, the male came out in defense of the female with which he had mated before. They only defend themselves, and the females that have been their partner; the other females remain defenseless. For this reason, the females worry about choosing the males that offer the greatest protection.
Some of the researchers argue that females of fiddler crabs often make visits to males outside the mating period.
In nature, it is the males who court the females until they yield to their requests; while females have the job of choosing the male that they want the most. In this specific case, it is the females who challenge the dangers of seagulls and other predators, in order to visit the males.
Moreover, they must be very cautious when choosing the male, because it represents not only the guarantee of procreation, but also the protection of her against contending rivals, and possible predators. So it is not seen as an act of prostitution, given that these crustaceans are not like some birds that form a couple forever. It is a mutual benefit, because not always the males are so successful with the females, so they have to resume their courtship again and again, until one of them accepts it. This search also entails being exposed to the dangers of fighting with other rivals for a female, and predators. On the other hand, when they have a female, they offer the sex that they look for and need, and in return they offer her the protection that she cannot give herself.
In general, the best thing is not to have any animal in captivity, because in spite of all the cares we can offer to them, they will never be better in another part, but in their natural environment. Crabs are animals that have a digestive system very different from that of humans, but people insist on feeding them as if they were one of the family. The alimentation is the most important care that you should offer to these crustaceans, since food is one of the main causes of death of crabs in captivity.
You cannot feed the crab with pasta, fruits, bread, vegetables, bananas, cookies, vegetables, or any other type of food that is cooked or not. Of course they will eat everything that is offered to them, more by instinct of preservation, than by hunger. But most of these foods are harmful to crabs, because they are very difficult to digest because of their digestive system.While you think your crab is healthy and in good shape, you are just killing him slowly. These animals are used to eat amphibian larvae, small fish, macro invertebrates, aquatic plants, algae, carrion, and other things, that unless you reside near a river, you won´t be able to offer to your crab. However, in specialized stores you can get a fish feed, which are good options for these species. Another care that you must offer your crab, is related with the environment where it is going to develop. As we mentioned earlier, the fish tank should be kept completely clean, with very clear water. You must also have rocks, logs, or pieces of wood where this crab can climb, and with a sandy bottom, which allows him to dig.
But above all you should be very aware of the animals that are going to share this ecosystem with your crab. You must be very careful not to introduce in it a fish that can be predator of this crustacean, neither larger crab that can take advantage of the small ones. You can also place small fish or even larvae of others, if you get them, which can serve as healthy food for the crab; and if a sick fish gets to die just don´t worry, since as we mentioned before, the river crabs are scavengers, and are known as vacuum cleaners. So, the dead body of the unfortunate will be a source of food for the crab. You must be very careful to give the crabs enough space, because they are a bit temperamental when defending their territory. So if you decide to have a number of crabs in your fish tank, you must take into account the size it must have, so that all crabs can live in harmony.
If you want to have one, you must learn first everything about fish tanks