It’s time to learn about the blue crayfish or Cheraz destructor in scientific terms, although marron and Yabie, are other common words that are used to refer to this species of crayfish
Table Of Content
Blue Crayfish´s Characteristics
This species of singular beauty has an exoskeleton whose color can vary between iridescent blue, orange or brown. All these characteristics obviously increase its beauty. Crustaceans are beautiful creatures that have many fans, especially those who are lovers of all species. However, the blue crab is one of the most striking species due to its colors.
Although not listed as an endangered species yet, the contamination of seas and rivers by humans, will not take long to make this happen.
The most common coloration of this crab is slightly brown, including its legs. As for its chelipeds they are usually slightly mottled between green or bluish, but this coloration will depend on the habitat, the place, and the individual.
Blue Crayfish´s Anatomy
Blue crayfish have an elongated body, which makes them different from other crabs, and at the same time, very similar to lobsters. (See our article crayfish for further information about this species)
The head and internal organs of these crabs are protected by the shell and the six segments of their abdomen are covered individually by a flexible membrane that facilitates their movement.
The cheraz destroyers have a pair of large claws on their frontal portion followed by four pairs of walking legs and four pairs of small swimming legs called pleopods, which are covered with fine hairs where the female carries her eggs.
The front clamps, are used by the blue crabs to feed, and also to dig up to two meters deep.
Additionally, they have a central fin on their tails, which is surrounded by four other fins that they use to move quickly through the water, as well as to completely roll up to form a nest. They have two eyes at the end of the appendages but the senses of touch and taste are much more important for them. They have a pair of large tentacles (or antennae) for that purpose.
All crayfish have their heads and internal organs protected by a carapace (shell), unlike the six segments of the abdomen, which are covered with a flexible membrane, but individually, in order to allow them move.
Blue Crayfish´s Common size
When the blue crayfish are in the proper conditions, they can measure between twenty-five (25) and thirty (30) centimeters long, and reach two hundred and fifty (250) grams of weight; of which twenty percent corresponds to the tail.
Main differences between both sexes
Although in appearance they can be very similar, these animals have marked differences. The first difference relies on the location of the genital pores. In the case female blue crabs, the reproductive organ is located at the base of the third pair of legs, and has an ovoid and transparent shape. While in the male, its reproductive organ is located at the base of the fifth pair of legs, and is a setoff of its exoskeleton, similar to the head of a pin. The other differences are easier to appreciate, because they are related with the size of the male, which is a bit larger compared to that of the female, as well as the robustness of its tweezers. On the other hand, the female owns the pleopods of its tail longer than the male, since she will lodge the clusters of eggs in them. Like the vast majority of crabs, blue crabs must molt their exoskeleton, once a year in the case of adult specimens. When they abandon their old shell, they ingest large amounts of water to fill their internal structures, and thus be able to increase in size. This allows them to have enough space to develop their internal muscles and organs. Once the molting has been carried out, little by little they begin to harden their new shell making use of their internal deposits of calcium.
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Blue Crayfish Habitat and Distribution
Although the blue crabs are often sensitive to environmental changes, these crustaceans have expanded and consolidated in diverse environments. This species of singular beauty can be found in the lowlands, specifically where there are different concentrations of water such as dykes, streams, wells, swamps, reservoirs. They usually prefer crystal clear waters, although they can also be found in other places, of different temperatures.
For this reason the blue crabs can adapt to warm streams as well as to cold lakes. These animals have a powerful advantage that is that they can live in seasonal water courses and survive the drought. The fact of being buried in the mud at a certain depth, and remaining in a state of lethargy, which can sometimes last up to a year, until the rains return, makes it easier for them to survive intense periods of drought. This condition also protects them from predators. The blue crayfish are freshwater and semi-aquatic creatures which need extensive vegetation, but above all, high levels of oxygen concentration in the water. Although they prefer waters with temperatures between twenty and twenty-five degrees, theYabies can also tolerate temperature ranges between 1 ° C and 35 °.
Blue Crayfish Distribution
The blue crayfish are distributed throughout the length and breadth of Australia, being Victoria and New Wales, the places where they are more popular. However, they can also be seen very often in southern Queensland, and in the south and north of the territory of this country. In some of these locations the blue crayfish have been considered an invasive species, since they compete with other local species, and displace them from their territories.
But given the commercial importance that the small crustaceans have reached, new populations have been introduced in the north and west of Australia; since the degradation of the natural vegetation, as well as the contamination of the waters by the human being, have made a dent in the ecosystem of the species, and of the blue crab themselves.
If we add the increase of predation, also for man’s sake, in a few years it will be an extinct species.
For this reason the Fisheries Management Law of Australia designated the ecosystem where they inhabit, as an ecological community in danger, and therefore the blue crab is classified as vulnerable in the IUCN red list
How Blue Crayfish Reproduce
These creatures are characterized by having a very short life cycle, and a rapid growth rate, as well as a very high fecundity. For this reason they have multiple spawning, reaching their reproductive age between the first four years of life.
The sexes of the blue crabs are separated, and unlike other species of crabs, the female spawns underdeveloped eggs. So, they need maternal care for a period of time which makes the female carries them in her abdominal appendix during that time.
This period will last, until the eggs hatch in juvenile crabs, which will be independent. It is very possible that the mother burrows during this time, not only to maintain a humid environment, but also to protect their young. Although fecundity will depend on the size and weight of the females, it is believed that they can produce 200 juvenile eggs approximately.
The reproduction of the blue crabs is conditioned not only by the duration of the day, but also by the temperature of the water. For this reason, mating in this species begins in the spring, when the temperature of the water has risen above fifteen Celsius degrees.
Just at this moment, the males that are well developed deposit a spermatophore between the fourth and fifth pair of legs of the female.
These small green oval-shaped eggs are immediately attached to the legs of the female crab, and will take between nineteen and forty days to hatch, depending on the temperature of the water. In general, this process is carried out two or more times, where the female is able to put up to one thousand (1000) eggs each spawn.
Lifecycle
Like all crustaceans, the blue crayfish must molt their shells (exoskeleton) periodically for growing. This type of growth is not continuous, it occurs in steps. The molting frequency depends on the length of the day and the temperature.
The frequency decreases along time. The newly hatched juveniles molt every few days, and when they reach more than three years they shed their carapace once a year. The new shell is very soft for a short period of time, and the yabbys are vulnerable to attack by other yabbies, fish and other predators. The pink and clean shell of the new molt contrasts vividly with the dirty and algae-covered shell of the blue crabs from the previous molting stage, especially in older specimens.
Growth depends mainly on water temperature, available food and population density. Within certain limits, the hotter the water, the faster the crayfish grows. This is because, like most cold-blooded animals, blue crabs depend on the environment for heat and cannot regulate their own body temperature.
Although the blue crabs can tolerate temperatures of up to 35 ° C, growth becomes more difficult at temperatures above 28 ° C.
Once the maturity is reached, the female grows more slowly than the male, apparently due to the greater effort dedicated to the spawning.
When a crustacean loses a limb (claw, leg or antenna), it will grow back, on the next molt of shell. However, unless the lost part is small, total regeneration will not be immediate and usually three or four molts will be needed to completely restore the limb.
Blue Crayfish´s Behavior
They are usually not aggressive animals, unless they are bothered or intimidated. For example, when another member invades their territory, patterns of aggressive behavior can be manifested, this being hardly normal, since they must defend their territory. In Australia, which is their place of origin, it has been shown that these crabs prefer places where the soil is less sandy, and more clayey. When these crustaceans get localities with these characteristics, they use agonistic behavior in order to displace even the native species of the site, with the sole purpose of being able to keep their favorite substrate for themselves.
The Younger specimens usually compete for food resources, while adults compete for females, and for territory. Blue crayfish tend to develop hierarchies that are based on dominance and size. The largest individuals rule in their type of society, and also inhibit the growth of the smallest individuals. This occurs thanks to aggressive behavior, product of competition for food, females, and territory. It is believed that the presence of large specimens causes a high level of stress in small individuals, since there have been cases of extreme aggression, to the point of even presenting a cannibalism among them. Their behavior is nocturnal, being the first hours of the night and before the dawn their most active moment of the day.
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Blue Crayfish´s Alimentation Habits
These creatures feed on a wide variety of waste or leftovers, algae, and also aquatic invertebrates. They are omnivorous by nature, and their main food is decaying vegetation. These crabs turn out also to be a sort of opportunists, because they can eat almost anything, such as mussels, snails, fish, frogs, plants, carrion, other crabs, and even smaller blue crabs. The latter doesn´t happen often, only when their food is scarce, and also when there is not enough space, and they feel cramped. They can also be insectivores, ingesting this type of bugs through zooplankton; and feed on diatoms, which are a type of unicellular algae, which can be ingested by filtering marine debris, by accident.
Blue Crayfish in Aquariums
When the species possess extreme beauty, all people want to have them in a special place in their home, to contemplate them whenever they want . However, the way to protect and maintain them must be known in order to give them the proper cares. The blue crayfish is an entertaining pet for aquariums and very easy to maintain. One or two large yabbies, or six to ten medium ones, would be suitable for a 100-liter tank. It is recommended to put stones or some kind of cover in the aquarium, so they can hide when they move.
Feed them with small amounts of plant debris, chicken granules and a little lean meat from time to time, eliminating what they don´t eat every day. The blue crabs can live several months without eating anything, so it is better to feed them with small quantities of food.
The Yabbies reproduce easily. No special food is required for young specimens, who will find remains lost by the mother. There should be sufficient coverage, such as aquatic plants, where juveniles can escape from adults.
The Aquatic plants should be tied to large stones to prevent the crab from plucking them while digging or searching for food; otherwise, use artificial plants
Keep the water level 5 cm below the top of the tank, to prevent the crabs from climbing up the air hose and crawling out.
Characteristics of the Water
In their natural habitat, these crabs are very resistant, and adapt to different environments, even some of them have survived living in dirty waters. But when they live in captivity, things fact changes a little, since to guarantee a the proper life quality to them, the water must have a Ph between 7 and 9, and a Kh (Carbonate Hardness) above 8, as well as a Gh (General Hardness) above fifteen points, so they can live in optimal conditions.
Moreover, the water must be well oxygenated at all times, so it is required an aerator that works constantly.
Ways to increase KH
Add baking soda (sodium bicarbonate). A teaspoon of baking soda added to 50 liters of water can raise the water kH by approximately 4 degrees without significantly affecting the pH.
Add commercially available products to increase buffering capacity
Ways to lower kH
Inject carbon dioxide (CO2)
Use reverse osmosis (RO) water. You can mix tap water with reverse osmosis water to achieve the desired KH.
Add products available in the market to reduce buffering capacity.
Ways to increase gH
Add limestone to the aquarium (this will also increase kH, which in turn will increase the pH)
Add calcium carbonate will raise gH and kH
Ways to reduce gH
Adding peat to your filter
Use commercially available water softening pillows or a water softener (this removes calcium and magnesium ions and replaces them with sodium ions.) Many people feel that this is an unacceptable method of softening water since many fish they prefer soft water they do not like sodium either.
Mixing tap water with reverse osmosis (RO) water.
What blue crayfish feed on in aquarium?
As we mentioned earlier, the blue crayfish is an omnivorous, detritivore and scavenger species; that is, it can feed on dead fish, plants, or food remains of other fish, and other types of crabs. In seasons of food shortages, they can commit cannibalism with the smallest specimens of your species. When the blue crayfish live in captivity, it is where their opportunistic characteristics emerges most, because they can eat everything that crosses their path. So, you can give them fresh foods of different origin, and frozen foods such as pieces of fish, bottom food, and seafood, among others. Take into account that vegetable food such as zucchini, spinach, carrot, as long as they are not raw and had been softened a little, can also be provided to them.
What do the blue crayfish need to reproduce in the aquarium?
As we saw before the crabs don´t require especial things to reproduce in captivity, the only thing they need to have a family in the aquarium, are the conditions mentioned above regarding the water temperature and the amount of light that this crustacean should receive. In the cold months it is advisable to maintain the temperature between twenty and twenty-two degrees; but when spring arrives, you should increase it little by little until twenty-five degrees. The aquarium water must remain clean and crystal clear, with the proper oxygenation. If your fish tank has caves, rocks and logs where the crabs can play and have fun during their courtship, and where the female feels safe depositing her eggs, then it is almost certain that she will succeed in reproducing the species.
Care of newborns
You must bear in mind, that if things go well, the female can put about one thousand (1000) eggs, so you should take your forecasts for future baby crabs. It is necessary to place shelters for newborns, which can be done with PVC tubes, and that are well anchored, so they have somewhere to hide from any danger. When the crabs are young they molt their carapace very often, which makes them very vulnerable. This fact makes them seek a place to hide, while this period lasts. That is why you should provide them with small tunnels, where the largest crabs can´t fit. If you have another fish tank, it is a good idea to isolate the smaller blue crabs, until they reach a size with which they can defend themselves.
Blue Crayfish´s Hunting
Catching blue crayfish or «yabbling» in rivers and dams is a popular summer activity in Australia. The fishing techniques vary from the most rudimentary, to some more sophisticated that employ large networks.
Local fishing regulations must be verified before using nets and traps for Blue Crabs. Many types of nets and traps are prohibited, since wildlife such as the platypus, water rats and long-necked turtles can get trapped in them and drown.
Aquaculture
The common blue crayfish are a popular species for aquaculture, although their burrows can destroy prey.Blue Crabs can also be found on privately owned dams where fishing permission must first be obtained. The limits of the bag apply to Blue Crabs in most states. For example, in South Australia it is illegal to capture more than 200 Blue Crabs per day. All females that carry eggs under their tails must be returned to the water. The commercial fishery for Blue Crayfish has been significant since 1973.
Before the 1970s, the blue crabyfish were relatively unknown as a dish. This fact changed soon when their export earnings increased dramatically, due to the shortage of Norway lobster in Europe as a result of the crayfish plague. Most of this export went to Sweden, where the freshwater crab is considered a delicacy and has a high price and where fishing has been banned for 50 weeks in the year.
In the rush to export, several processing companies in southern Australia hired the majority of blue crabs fishermen, guaranteeing a high price for their catches.
During the following years, almost all of Australia’s blue crabs were exported.
But the industry collapsed as suddenly as it had emerged. By 1978, the fishing grounds had failed, with catches that drastically decreased from more than 100 to less than 10 kilograms / man / day. Suggested reasons for the accident include overfishing, competition from a growing number of carps and the natural cycle of «boom and bust» in blue crabs populations. During the last decade, blue crab lands have been gradually recovering from the exploitation of that time. There are regulations that govern the type and quantity of equipment allowed for fishing blue crabs. Certain regions are often closed to traps or networks. Since such laws may change from time to time, the catchers must consult their local Fisheries Officer for updated information.
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