The Signal crayfish (Pacifastacus leniusculus) is a relatively large freshwater crustacean with a reputation of being an invasive species. Nonetheless, it does not stop people from keeping them as pets in their home aquariums.
Pacifastacus leniusculus is a very prolific and adaptable species. Being omnivorous invertebrates, Signal crayfish grow and mature fast.
If you are thinking of keeping the Signal crayfish as pets, or simply want to learn more about this species, you have come to the right place.
Based on existing studies, experiments, research, and the experience of enthusiasts, this complete care guide for Signal crayfish covers all aspects of their life and how they should be cared for within your tank.
|Important: Pacifastacus leniusculus (the Signal crayfish) is one the most widespread and one of the most successful invasive crayfish species in Europe.
Even if it is not banned in your state or country, NEVER release the Signal crayfish into the wild!
Pacifastacus leniusculus carries crayfish plague (Aphanomyces astaci) to which it is resistant but which is lethal to most other crayfish species. In addition, it can alter ecosystems, causing the loss of native species, harming fisheries, and having major economic consequences.
Quick Notes about Signal Crayfish
|Scientific Name||Pacifastacus leniusculus|
|Other names||the California crayfish|
|Tank size (minimum)||15 gallons (~60 liters)|
|Average size||up to 3 – 4 inches (7 – 10 cm) long|
|Optimal Temperature||50 – 70°F (10 – 21°C)|
|Optimal PH||7.0 – 8.5|
|Optimal GH||3 – 25|
|Life span||up to 20 years|
|Color Form||Dark brown|
Distribution of Signal Crayfish
Pacifastacus leniusculus is endemic to northwestern America and southwestern Canada. Nowadays, these crayfish can be found in over 20 countries in Europe (Austria, Belgium, Cyprus, Denmark, Finland, France, Germany, Greece, Italy, Japan, Latvia, Lithuania, Luxembourg, Netherlands, Poland, Portugal, Russian Federation, Spain, Sweden, Switzerland, United Kingdom), Asia and even South Africa.
Interesting fact: Signal crayfish were widely introduced into many parts of Europe and Asia in the mid- to late 1900s to compensate for the loss of native European and Asian species caused by the crayfish plague. The sad thing though is that that plague started from the previous introduction of this species. Unfortunately, the mistake was discovered when it was already too late.
Habitat of Signal Crayfish
The Signal crayfish inhabit both freshwater bodies, such as ponds, lakes, streams, rivers, and even low saline waters.
This species does not have a preference and can be found in rocky, muddy, and vegetated areas.
Description of Signal Crayfish
This species has massive claws that affect their weight. For example, a 3-inch male and female generally weigh 5.5 oz (158 g) and 4 oz (115 g) correspondingly.
Signal crayfish are easily identified by the white color in the ventral face of their large and robust claws. The overall color of these crayfish is dark brown.
Lifespan of Signal Crayfish
According to the study, Signal Crayfish are long-lived animals. Based on a neuronal age pigment, the assessment of average estimated longevity of this species is between 6 and 16 years, with some individuals able to live up to 20 years.
Growth of Signal Crayfish
According to the study, these crayfish have a fast rate of growth, reaching 4 inches (10 cm) of total length only after 3 years. Such individuals start molting only once a year while younger ones molt more often, for example:
- 2 times (smaller than 3 inches crayfish)
- 3 times (smaller than 2 inches crayfish)
After hatching, the juveniles molt for the first time after 2 weeks. After 3 months, they grow up to 1 inch (26.5 cm).
Crayfish are highly vulnerable to predation and to adverse environmental factors during molting.
Interesting fact: Males grow faster than females by a larger per molt increment and more frequent molt.
Typical Behavior of Signal Crayfish
Crayfish are fully aquatic animals. They require permanent bodies of water for survival since they live in open water.
Signal crayfish are highly nocturnal animals, according to the study, with less than 6% of movements recorded during daylight hours. Generally, they emerge from their hiding places to forage after dark and are capable of substantial active movements.
These crayfish are classified as secondary burrowers. It means that they do not rely on burrows and do not spend all of their time there. However, if the environment (substrate) allows they may dig burrows.
Signal crayfish have very simple, straight burrows with somewhat angular chambers, with a single opening below the water surface. In most cases, their depth range from 6 – 26 inches (15 – 65 cm).
- Unlike the majority of smaller crayfish, large males (over 4 inches or 10 cm) rarely make burrows even when there are no natural shelters. This is probably because of the fact that large males have bigger and more powerful claws than females and/or juveniles and appear not to shelter from potential predators that often.
- Juveniles can make a burrow within an hour whereas whereas adults may often spend several hours or even days in order to complete the excavations.
- When they return to the burrows, they check them for intruders before they enter (tail first).
Signal crayfish are territorial and require a lot of space to cut down on their naturally aggressive temperaments. However, their aggressive activity can decline with the increasing availability of both shelter and food.
- Social: No
- Active: No
- Peaceful: No
- Territorial: Yes
- Burrowers: Yes
Diet of Signal Crayfish
Signal crayfish are benthic omnivorous and detritivorous feeders.
It means that they can feed on a variety of items. According to the study, a total of 22 food groups were categorized from their gut contents including fish eggs and larvae, insects, macroinvertebrates (snails, worms, other crayfish, etc.), small invertebrates (tadpoles, etc.), algae, macrophytes, dead leaves, plants, etc.
Direct predation of fish, as well as cannibalism, occurred. However, fish are usually predated mostly by adult Signal crayfish. Cannibalism increased mainly with crayfish size.
Note: There is some conflicting information regarding juvenile crayfish. In most crayfish species, juveniles are primarily carnivorous to get a clear growth advantage. However, there are also reports that, in Signal crayfish, juveniles consumed food types that were just the opposite of those purported to be of most nutritional value to them (such as detrital matter, needles, leaves, etc.).
Detritus and green algae (Cladophora) are ingested most frequently by all sizes of crayfish throughout the year.
Signal crayfish mainly feed at night. The estimated ratio of a day ranged from 0.22 to 6.02 % of wet body.
In captivity, for the best growth, the Signal crayfish diet should consist of about 80% vegetation and 20% protein-based food.
If these crayfish are kept as pets in aquariums, suggested foods include (some links to Amazon):
- crushed snails,
- brine shrimp,
- dead fish or shrimp,
- Artemia sp.
- Shrimp pellets,
- Shrimp Granules,
- Shrimp food (Hikari’s crustacean food like Hikari Shrimp Cuisine),
- Frozen blood worms, etc.
- Diet Type:
- Food Preference: Mix of meats and vegetation.
- Feeding Frequency: 3 – 4 times a week for adults. Daily for juveniles.
Rules of Diet in Captivity for Signal Crayfish
- Leave their food for 24 hours before removing it. To prevent water contamination, leftover feed should be removed by siphoning before fresh food was added. Leaves can be left for several days in the tank.
- Leave old exoskeletons. Do not remove molted exoskeletons. They will eat it later.
- Check their hiding places. Keep in mind that Signal crayfish often drag and store food in their hiding spots for later consumption. Check them from time to time to prevent any bacterial contaminations.
- Crayfish need diversity in food. Do not give them the same food all the time. Change their diet periodically.
Are Signal Crayfish Plant Safe?
No, they are not. Signal crayfish will eat, cut, and shred almost any plant they can get.
It is not recommended to keep them in planted tanks. The only viable options for this species are:
- plastic plants,
- floating plants,
- some cheap plants that you are ready to lose.
Tank Requirements and Water Conditions
Signal crayfish care is quite simple and straightforward. These crayfish can thrive in most situations and easily adapt well to life in captivity.
Nonetheless, if you want to make them happy, you still need to address their core needs. Here are some care guidelines to help you out.
Crayfishes need a lot of space to move in the tank. A 15-gallon (60 liters) tank is recommended minimum for one adult Signal crayfish. Juveniles can be kept in the smaller tanks but they will quickly outgrow it.
Main reasons to have a larger tank:
- The bigger the tank, the better it may be to set up diverse areas for them to dwell and hide.
- Crayfish produce a lot of waste! So, it can be easier to keep your water parameters stable.
Important: Signal crayfish are great escape artists and will climb air hoses and silicon sealant because of this, you should place a fitted lid on the tank. When keeping any type of crayfish, it is a good idea to make sure the water line in your aquarium is not too high.
If you are a first-time crayfish owner it is important that you cycle your tank before bringing any crayfish home. Once the tank is cycled you need to check the quality of the water using a test kit.
Temperature: Signal crayfish do not like too warm temperatures. According to the experiments, the ultimate upper lethal temperature for this species was 87.98°F (31.1°C).
Note: After 70 days, at 77 °F (25°C), crayfish became sluggish. The percent survival drastically reduced above 79°F (26 °C) and some crayfish started dying from an abnormal molt.
Thus, their preferred water temperature is between 50 – 70°F (10 – 21°C). This temperature range is considered optimal for the Signal crayfish.
pH: Signal Crayfish require water with a pH of greater than 7.0. Ideally, pH should be in the range of 7.0 – 8.5.
Note: Low pH impedes crayfish’s calcium absorption and thus weakens their carapaces, which increases their mortality rates.
Hardness: They will appreciate optimal KH 3 – 20 and GH between 3 – 25 GH.
Salinity: Signal crayfish are hardy enough to tolerate salinity levels for some time. Experiments showed that they survive over 9 weeks with salinities up to 28 PSU. However, females with eggs have not been seen at salinities above 7 PSU.
As long as there are many hiding places, there is no need for a deep substrate. However, if you decided to have one, a steeply sloping bed suitable for burrowing will be the best choice.
Avoid completely flat and soft bottoms.
In their natural habitat, the percentage of the bed covered with cobbles and small stones typically varies between 7% and 100%.
No special requirements. Signal crayfish are nocturnal animals.
If you have plants, lighting should be adapted to their needs.
Having sponge filters in the aquarium with Signal crayfish is just a very bad idea. The point is that these crayfish will definitely chip, chew and break apart the sponge.
Therefore, Hang on the back or canister filters will be a better choice.
The shelter is an important and limited resource for crayfish. Signal crayfish often hide in a shelter under driftwood, between rocks, and in a burrow. Thus artificial shelters are essential and they should be abundant!
Providing shelter during the mating season is important as it offers protection during periods of vulnerability such as molting, protects the broodstock against predation, and minimizes aggressive interactions.
Stacks of PVC pipes, mesh bundles, driftwood, etc. provide enough shelter, especially in the grow-out phase.
Sexing Signal Crayfish
Pacifastacus leniusculus exhibits obvious sexual dimorphism.
- The females have a greater total length and a wider abdomen, while males have a higher weight and larger claws than females.
- Male crayfish lack hooks on the 3rd segment of the walking legs, while females lack the seminal receptacle, which is located between the 4th and 5th pairs of walking legs.
Breeding Signal Crayfish
Females reach sexual maturity in the 3rd year and males in the 2nd year approximately at a size of 1.4 inches (or 36–38 mm) of the carapace or about 3 inches (or 8 cm) total length.
Note: The recorded smallest berried female was 36.3 mm (carapace length) corresponding to an age of 2+.
Signal crayfish spawn eggs within one week, usually 2−3 days, after mating.
Note: Only about 90% of females are ready to reproduce annually.
There is a positive correlation between the size of females and the number of eggs as larger females produce more eggs.
According to multiple studies, females of this species can usually have anywhere between 130 – 724 eggs per brood. Large females can often carry more than 500 eggs. Eggs are attached to the females throughout the whole embryonic development.
The egg diameter and the egg weight are 2.40 – 2.88 mm and 0.007 to 0.012 g respectively.
In Pacifastacus leniusculus, ovaries mature between July and January; oviposition occurs between October and February; young hatched in May to July.
Basically, because of the low temperature in their natural environment, it takes several months for the eggs to hatch.
Note: Experiments showed that females held at an average of 44°F (6.8°C) failed to hatch eggs.
The mean size of newly hatched Signal crayfish juveniles is 0.38 inches (9.7 mm). After hatching, they remain with their mother for several weeks then they leave their mother as completely independent miniature adults.
Generally, there is no cannibalism of eggs and young by brooding females.
Signal Crayfish and Suitable Tankmates
Pacifastacus leniusculus is an aggressive and territorial species. Therefore, it will be right to say Signal crayfish do not have suitable tank mates.
The Signal crayfish have been observed going after the nests of fish at night and predating fish eggs. In the long run, small community tank fishes and shrimp have no chance against the claws of these crayfish.
At the same time, larger and/or aggressive fish will hunt down Signal crayfish.
Overall, it can be pretty complicated to put other creatures in the same tank with the Signal crayfish. The ideal situation is a species-only tank with a lot of hiding places to reduce aggressive behavior.
Signal crayfish is a very easy animal to care for in home aquarium even for beginners. Nonetheless, be very careful and never release them into the wild.
Pacifastacus leniusculus is very tolerant to environmental extremes, such as temperature and various pollutants. Its aggressive nature, combined with its prolific breeding habits allows them to out-compete most other crayfish species.
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