Rusty Crayfish Profile – Detailed Guide

Rusty Crayfish Profile - Detailed Guide

Faxonius rusticus, also known as the Rusty crayfish, does not have a good reputation because of its invasive nature.

Rusty crayfish are aggressive and extremely adaptable species. These crayfish grow and mature fast. Once established, they are extremely difficult to nearly impossible to eradicate.

If you consider keeping Rusty crayfish as pets in your aquarium, or you simply want to know more about this species, over the following few pages, this complete profile covers all aspects, from natural habitat conditions, behavior, feeding preferences, breeding, etc.

Important: Faxonius rusticus (the Rusty crayfish) is one the worst invasive crayfish species in North America. Legislation has been passed in many states to prevent the introduction, sale, or possession of this invasive species.

Even if it is not banned in your state or country, NEVER release the Rusty crayfish (Faxonius rusticus) into the wild!

The introduction and spreading of non-indigenous species of aquatic fauna has caused and still causes, strong ecological impacts in freshwater environments worldwide. This is one of the leading threats to freshwater biodiversity.

Quick Notes about Rusty Crayfish

Name Rusty crayfish
Scientific Name Faxonius rusticus
Tank size (optimal) 20 gallons (~80 liters)
Keeping Easy
Breeding Easy
Size up to 3 – 5 inches (7 – 12 cm) long
Optimal Temperature 68 – 77°F (20 – 25°C)
Optimal PH 7.0 – 8.0
Optimal GH 3 – 25 
Diet Omnivore / Carnivore
Temperament Aggressive
Life span up to 4 years
Color Form From greenish-grey, light to reddish-brown

Taxonomy of Rusty Crayfish

Originally, the Rusty crayfish were known as Cambarus rusticus (this name was initially assigned to this species in 1852).

In 1872, these crayfish were moved to the genus Orconectes (Orconectes rusticus). Faxonius rusticus is a newer name assigned to the species only in 2017.

Note: The change from Orconectes to Faxoniusis based on a separation of cave-dwelling (Orconectes) and non-cave dwelling (Faxonius) species of crayfish.

Origin of Rusty Crayfish

This crayfish is native to the United States of America. It is home to the Ohio River Basin (which covers southeast Illinois, Indiana, Ohio, West Virginia, Tennessee, Kentucky, and parts of Alabama, Virginia, and North Carolina.

Nowadays, these crayfish were reported to occur in 33 states in the USA., and 3 Canadian Provinces.

There are assertions that they got there because they were used as live bait by anglers or intentional release by lake managers seeking to manage macrophyte communities.

Interesting fact: This species was first caught in 1973 in Illinois. Rusty crayfish are rapidly spreading across the east of North America. The expansion and spread of rusty crayfish have resulted in the displacement of native crayfishes in these places. As an invasive species, several measures have been put in place by authorities to put its population and spread under control.

Habitat of Rusty Crayfish

Rusty crayfish is a freshwater crayfish species that thrives in freshwater streams, rivers, lakes, and ponds. They prefer areas with rocks, logs, and trees for cover and shelter.

This species is a habitat generalist. Rusty crayfish thrive both in areas of high flow (rivers and streams) and standing water (lakes and ponds) with gravel, cobble, or sand substrate.

Although this species prefers clear well-oxygenated waters with diverse habitats and available shelter/cover objects, it does not limit their expansion.

In nature, Rusty crayfish are predominately found in less than 3 ft. (1 meter) of water but have been found as deep as 45 ft. (14.6 meters).

Appearance of Rusty Crayfish

Rusty Crayfish Profile - Detailed Guide
National Park Service photo

Rusty crayfishes are not small crustaceans.

With average carapace lengths greater than 2.5 inches (6 cm), they are relatively large species of crayfish. In total length, Rusty crayfishes reach up to 5 inches (10 cm).

In terms of relative magnitude, these crayfishes have particularly sizable claws compared to other crayfish species. Their claws can be almost the size of the carapace.

In most cases, crayfish can be hard to identify but not with this species. Rusty crayfish can be easily identified by their carapace and lateral surface of the claws.

  • Their coloration ranges from greenish-grey, light to reddish-brown always displaying a dark red (rusty) spot on either side of their carapace just before the tail, hence the common name the Rusty crayfish was derived.
  • The dorsal portions of their carapace typically display a U-shaped dark brown saddle that extends anteriorly, and abdomen segments often appear dark-brown with W-shaped patches that are also dark brown.
  • Rusty crayfishes also have large robust claws that are gapped at the base when closed and are often red-tipped followed by black bands.

Lifespan of Rusty Crayfish

According to the study, it was found that Rusty crayfish can live up to 4 years.

Typical Behavior of Rusty Crayfish

Rusty crayfish are fully aquatic animals. They require permanent bodies of water for survival since they live in open water.

Unlike many other crayfishes, this species is known to be a non-burrower. However, they may do some shallow burrowing (characterized by a simple tube-shaped burrow oriented horizontally) into debris and underside of rocks during periods of temperature extremes or when no other structural habitat is available.

Generally, they prefer to find shelter under rocks and logs.

In addition, Rusty crayfish are very aggressive creatures that engage in frequent agonistic interactions over access to resources, including shelters. In nature, they often compel other crayfishes to hide or move away, giving them a competitive advantage.

Their aggressive nature peaks when they meet each other.  They take a posture, ready to fight. Their constant fights are a way to assert dominance — as the crayfish with the most wins gets placed in the hierarchy.

Interesting fact: Crayfish communicate with each other through urine — yes, urine! The smell of the urine is a chemical cue to one another. When they meet for the first time, they release urine as a form of communication. The stronger the odor, the less time for aggressiveness and wrestling.

Crayfish are generally crepuscular but Rusty crayfish displayed diurnal and nocturnal activity.

This is also a relatively active species. However, peaks of higher locomotor activity alternate with longer periods of slow or null speed.

According to the study, they spend equal proportions of time immobile and walking (50% immobile vs. 50% walking).

In aquariums, a frequently observed behavior is “wall-following” in which Rusty crayfish walking parallel to a wall will trail the end of one of its antennae along the wall, using the surface texture to navigate.

Features:

  • Social: No
  • Active: Yes
  • Peaceful: No
  • Territorial: Yes
  • Burrowers: No

Diet of Rusty Crayfish

Rusty Crayfishes are voracious eaters. They have a greater metabolic rate and enormous appetite than most crayfish species.

This species is an opportunistic omnivore that can feed on a variety of food items. In the wild, they consume snails, insects, fish eggs, small fishes, veggies, aquatic plants, algae, and detritus.

According to the study, detritus was the most abundant food item in the guts across months, ranging from 44–65% of the overall diet. Plant material and algae were also found in all collection months.

Rusty crayfish can undergo seasonal diet shifts to match their resource use to the available resources in their environment. For example, the abundance of animal, plant material, and algae in the guts increased during the summer months and decreased during fall and early spring. Whereas the diatom contributions to the diet were highest in the spring months.

In captivity, for the best growth, Rusty crayfish need a good mix of meats and vegetation, where their feeds should contain protein at a level of about 20 – 30% of the diet.

If Rusty crayfish are kept as pets in aquariums, suggested foods for these crayfish are (some links to Amazon):

Features:

  • 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 Rusty 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 to improve health.
  • Check their hiding places. Keep in mind that 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.

Rusty Crayfish: Calcium and Molting Cycle

Calcium (Ca) is an essential component of the exoskeleton composition of all crayfish species and the Rusty crayfish is not an exception.

In order to grow and/or restore lost limbs, Rusty crayfish must regularly molt (shed the old exoskeleton).

Growing a new exoskeleton requires a high amount of Ca to facilitate calcification. The process of molting puts crayfish in a vulnerable state.

Related articles:

Are Rusty Crayfish Plant Safe?

No, they are not. Rusty 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.

Related articles:

Tank Requirements and Water Conditions

Rusty crayfish are extremely adaptable species and can thrive in most situations.

In aquariums, though, it is better to replicate their natural environment. Therefore, you still need to address their core needs! Here are some care guidelines to help you out.

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.

Tank Size:

Crayfishes need a lot of space to move in the tank. A 15-gallon (60 liters) tank is recommended minimum for one Rusty crayfish. A 5 or 10-gallon tank is too small to keep a large, adult Rusty crayfish.

Start with a 20-gallon tank. You can consider larger tanks too. Some reasons to have a larger tank:

  • The bigger the tank, the better it may be to set up with 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.

Tip: Rusty 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.

Water Parameters:

Temperature: Rusty Crayfishes can endure extreme temperatures. In their natural habitat, they can survive temperatures from near 32 – 95°F (0 – 35°C). But that does not necessarily mean that they thrive at the upper and lower points of their temperature tolerances.

Therefore, their preferred water temperature is between 68 – 77°F (20 – 25°C). This temperature range is considered optimal for the species.

Note: Crayfish are coldblooded and thus are less active in colder temperatures.

pH: Observations showed that Rusty Crayfish prefer water with a pH of greater than 5.5 and dissolved calcium above 2.5 mg/L. Ideally, ph should be more than 7.0.

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.

Lighting:

Although Rusty crayfish can be active even during the day, they are still considered nocturnal animals.

Therefore, no special requirements. However, if you have plants, lighting should be adapted to their needs.

Related article:

Aeration and Water Flow:

Rusty crayfish will appreciate a well-oxygenated tank but this is not strictly necessary.

Substrate:

In nature, Rusty crayfish use their adaptability to various types of habitats. Basically, this species can inhabit all substrates but prefers a cobble habitat composed of small rocks, gravel, and lots of boulders.

They use rocky habitats as shelter from cannibalism and predation over alternative substrates like sand or muck.

Décorations:

The main purpose of décor is to provide hiding places to mimic the natural habitat as much as possible.

Shelters are important as they offer protection during periods of vulnerability such as molting, protect the young crayfish against predation, and minimize aggressive interactions.

Stacks of PVC pipes, mesh bundles, driftwood, etc. should always be more than the number of crayfish to reduce competition and cannibalism.

Note: Rusty crayfish are aggressive towards each other and cannibalism after molting can become a huge problem.

Related article:

Breeding Rusty Crayfish

Maturity:

Males and females become mature at an identical size when their carapace length reaches 0.6 inches (1.5 cm).

Sexing Rusty Crayfish:

  • Size. Sexual dimorphism is observed with males often having larger chelae and being slightly larger overall than females.
  • Reproductive organs. Males have2 corneous central projections each with a smaller non-corniculate median process and the rear surface displaying a strongly angled shoulder. Females have a nearly rhomboidalannulus ventral is with a trench through the anterior portion and two posteriorly facing projections that extend over the central depression.

Mating:

In nature, mature Rusty crayfish mate in late summer, early fall, or early spring, and achieve high growth rates. Generally, reproduction can occur twice a year.

When a female is ready to mate, she will allow a male to clamp her claws and put her on the back.

Females can store semen until their eggs are ready to be fertilized. They begin to lay their eggs as soon as water temperatures rise.

Interesting fact: In Faxonius rusticus, females are attracted to pheromones produced by males during breeding seasons. However, males do not show a preference for female signals.

Eggs:

Females carry fertilized eggs in the underside of their tails sections called “swimmerets.” Their eggs have deep red or maroon color.

Rusty crayfish can carry anywhere from 80 to 575 eggs. Minimum egg counts for the 29 ovigerous females. Fecundity is strongly correlated to the size of sexually mature females.

Hatching:

Depending on the temperature, on average, eggs hatch after 20-30 days. Upon hatching, juveniles will stay near the mother for several weeks. After that, they become completely independent.

Juveniles were recorded having greatest survivability between 68 – 77°F (20 – 25°C) but exhibit optimal growth between 79 – 82°F (26 – 28°C).

Once maturity is reached, growth rates slow considerably.

Rusty Crayfish and Suitable Tankmates

Since Rusty crayfishes are quite aggressive, it is safe to say they do not have suitable tank mates.

This species is too territorial and hostile. They are hostile to fishes, other species of crayfishes, crabs, dwarf frogs, and especially snails.

The Rusty crayfish have been observed going after the nests of fish at night. In the long run, small community tank fishes and shrimp have no chance against the claws of these crayfishes.

At the same time, larger and/or aggressive fish will hunt down the Rusty crayfish.

Overall, it can be pretty complicated to put other creatures in the same tank with the Rusty crayfish. The ideal situation is a species-only tank with a lot of hiding places to reduce aggressive behavior. 

Conclusion

Rusty crayfishes are aggressive and adaptable aquatic creatures. They are opportunistic omnivore and can feed on a variety of food items. All these features make them low-maintenance animals even for beginner aquarists.

However, be careful and check your state laws – Rusty crayfish are banned in many states because of their invasive nature.

References:

  1. Guiaşu, Radu Cornel, and Mark Labib. “The unreliable concept of native range as applied to the distribution of the rusty crayfish (Faxonius rusticus) in North America.” Hydrobiologia 848, no. 6 (2021): 1177-1205.
  2. Messager, Mathis L., and Julian D. Olden. “Phenotypic variability of rusty crayfish (Faxonius rusticus) at the leading edge of its riverine invasion.” Freshwater Biology 64, no. 6 (2019): 1196-1209.
  3. Wood, Tyler C., and Paul A. Moore. “Big and bad: how relative predator size and dietary information influence rusty crayfish (Faxoniusrusticus) behavior and resource-use decisions.” Canadian Journal of Zoology 98, no. 1 (2020): 62-72.
  4. Kamran, Maryam, Megan E. Moore, and Paul A. Moore. “Homing behavior following shelter displacement in two crayfishes, Creaserinusfodiens (Cottle, 1863) and Faxoniusrusticus (Girard, 1852) (Decapoda: Astacidea: Cambaridae).” Journal of Crustacean Biology 38, no. 5 (2018): 531-538.
  5. McGill, Kyle. “The Life History of Faxoniusrusticus (Girard, 1852) in Sunfish Creek, Monroe County, Ohio.” (2018).
  6. Lorman, J.G. 1980. Ecology of the crayfish Orconectes rusticus in northern Wisconsin. Ph.D.Dissertation, University of Wisconsin, Madison, Wisconsin
  7. Tran, MARK V., and A. Manning. “Seasonal Diet Shifts in the Rusty Crayfish, Faxoniusrusticus (Girard). 5.” (2019).
  8. Hartzell, Sean M., Amber L. Pitt, and Steve Davis. “Invasive rusty crayfish (Faxonius rusticus) are diurnally more exposed than an imperiled native congener.” Journal of the Pennsylvania Academy of Science 95, no. 1 (2021): 17-27.
  9. Olden, Julian D.; McCarthy, Julia M.; Maxted, Jeffrey T.; Fetzer, William W.; Vander Zanden,
    Jake (2006). “The rapid spread of rusty crayfish (Faxonius rusticus) with observations on
    native crayfish declines in Wisconsin (U.S.A.) over the past 130 years”. Biological Invasions.
  10. Homan, Robert C. “Creating a Distribution Model of Invasive Rusty Crayfish (Faxonius Rusticus) in Michigan Streams Using Publically Accessible Data.” (2020).
  11. Luscavage, Elizabeth. “Female Invasive Crayfish Faxonius Rusticus Prefer Pheromones of Conspecific Males During the Breeding Season.” (2021).
  12. Florey, Cassidy L., and Paul A. Moore. “Analysis and description of burrow structure in four species of freshwater crayfishes (Decapoda: Astacoidea: Cambaridae) using photogrammetry to recreate casts as 3D models.” The Journal of Crustacean Biology 39, no. 6 (2019): 711-719.

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