Crayfish

Crayfish are also called crawdad or crawfish, which is any of numerous crustaceans (order Decapoda, phylum Arthropoda) constituting the families Parastacidae, Astacidae (Northern Hemisphere), and Austroastracidae (Southern Hemisphere). They are related closely to the lobster. Over half of the more than 500 species takes place in North America. Nearly all live in freshwater, although some species take place in saltwater or brackish water. The crayfish scientific name is Cambarus sp.

Characteristics of Crayfish

Crayfish can be characterized by the thorax and a joined head, or midsection and a segmented body that is sandy yellow, red, green, or dark brown in colour. The compound eyes are on the movable stalks, and the head has a pointed snout. The exoskeleton, or the body covering, is thin and tough. The front pair of the five pairs of legs holds large and powerful pincers (chelae). On the abdomen, there are five pairs of tiny appendages that are mostly utilised for circulating water and swimming for respiration.

The below figure shows a Crayfish fish in a freshwater aquarium.

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Most adult crayfish are up to 7.5 cm (3 in) long. Among the smallest is given as the 2.5-cm-long Cambarellus diminutus of the south-eastern US. Among the largest is the Astacopsis gouldi of Tasmania that may reach 40 cm in length and weigh up to 3.5 kg (8 pounds).

Crayfish fishes are common in streams and lakes and often conceal themselves under logs or rocks. They are very active at night when they feed largely on snails, worms, insect larvae and amphibian tadpoles; a few eat vegetation. Crayfish mate in the autumn and they lay eggs in the spring. The eggs, which are attached to the abdomen of females, hatch in 5 to 8 weeks. The larvae remain on the mother for many weeks. Sexual maturity can be achieved in some months to many years, and the life span ranges from 1 - 20 years, based on the species.

The common genera of North America include Orconectes, Procambarus, Cambarus, Faxonella, Pacifastacus and Cambarellus. Austropotamobius, the most common genus of Europe, is the only single native to Great Britain. The genus Astacus takes place in Europe and the genus Cambaroides in East Asia.

Geographical Distribution and Classification

Four extant families of crayfish are defined, three in the Northern Hemisphere and the remaining ones in the Southern Hemisphere. The Southern Hemisphere (called Gondwana-distributed) family Parastacidae, with 14 extant genera and two2 extinct genera, live(d) in Madagascar, South America, and Australasia.

They are differentiated by the absence of the pleopods' first pair. The three genera of the Astacidae, of the other three Northern Hemisphere families, live in western North America and western Eurasia, while the 15 genera of the family Cambaridae and the single genus of Cambaroididae, which live in eastern North America, eastern Asia, and Mexico.

North America

The greatest diversity of the crayfish species is found in south-eastern North America, with around 330 species in 9 genera, all in the Cambaridae family. A further genus of astacid crayfish can be found in the Pacific Northwest and the headwaters of a few rivers east of the Continental Divide. Also, several crayfish are found in lowland areas where the water is abundant in calcium, and oxygen rises from the underground springs.

In 1983, Louisiana designated the crawfish or crayfish, as they are commonly known as its official state crustacean. Louisiana produces 100 million pounds of crawfish per one year, with the white river and red swamp crawfish being the primary species harvested. Crawfish are a part of the Cajun culture dating back hundreds of years. A wide range of cottage industries has developed as a result of the commercialized crawfish iconology. Their products are crawfish attached to the wooden plaques, crawfish pendants, T-shirts with crawfish logos, earrings, and necklaces made of either silver or gold.

Anatomy

A decapod crustacean body, such as a lobster, crab, or prawn (or shrimp), is made up of 20 body segments grouped into 2 main body parts, the abdomen and the cephalothorax. Each segment may possess a pair of appendages, although, in multiple groups, these may be missing or reduced. Crayfish can reach a length of 17.5 cm (6.9 in) on average. In the end, the walking legs contain a small claw.

Uses of Crayfish

Food

Crayfish or big crayfish are eaten across the world. Like the other edible crustaceans, only a less portion of the crayfish's body is eaten. In many prepared dishes, such as bisques and soups, only the tail portion is served. At crawfish boils or the other meals where the whole body of the crayfish is presented, the other portions, such as the claw meat, can be eaten.

The production of global crayfish is centred in Asia, mainly in China. In 2018, Asian production accounted for 95% of the crawfish supply across the world.

In the US, as of 2018, crayfish production is strongly centred in Louisiana, with 93% of crayfish farms located in the state. In 1987, Louisiana produced 90% of the crayfish harvested in the world, 70% of which were locally consumed. In 2007, the Louisiana crayfish harvest was up to 54,800 tons, almost all of it from aquaculture. Up to 70–80% of crayfish produced in Louisiana are Procambarus clarkii (also called red swamp crawfish), with the rest 20–30% being Procambarus zonangulus (called white river crawfish). Optimum dietary nutritional requirement of freshwater crayfish or big crayfish, nutrient specifications are available for aquaculture feed producers now.

Bait

Crayfish are preyed upon by a wide range of ray-finned fishes and are commonly used as bait, either live or only with the tail meat. Catfish, smallmouth bass, striped bass, largemouth bass, perch, pike, and muskies are all attracted to them. When using the live crayfish as bait, anglers prefer to hook them between their eyes, piercing through their pointed and hard beak, which causes them no harm; thus, they remain more active.

When using the crayfish as bait, it is essential to fish in a similar environment where they were caught. An Illinois State University, located in the US, report that focused on studies conducted on the Fox River and Des Plaines River watershed has stated that rusty crayfish, initially caught as bait in a varied environment, were dumped into the water and "outcompeted the native clearwater crayfish."

The other studies confirmed that transporting crayfish to various environments has led to multiple ecological problems, including the native species elimination. Also, transporting crayfish as live bait has contributed to the spread of zebra mussels in multiple waterways throughout North America and Europe, as they are known to attach themselves to the exoskeleton of crayfishes.

Pets

Crayfish can be kept in freshwater crayfish aquariums as pets. They prefer foods like shrimp pellets or multiple vegetables but will also eat regular crayfish food, tropical fish food, small fish and algae wafers that can be captured with their claws. A report given by the National Park Service, video and anecdotal reports by aquarium owners as well indicates that crayfish will eat their moulted exoskeleton "to recover the phosphates and calcium contained in it."

As omnivores, crayfish will eat almost everything; thus, they can explore the edibility of aquarium plants in a fish tank. However, most of the dwarf crayfish species, such as Cambarellus patzcuarensis, will not destructively eat or dig live aquarium plants.

In a few nations, such as the United States, United Kingdom, New Zealand and Australia, imported alien crayfish are a danger to the local rivers. The 3 species commonly imported to Europe from the Americas are Pacifastacus leniusculus, Procambarus clarkii and Orconectes limosus. Crayfish can spread into various bodies of water due to the specimens captured for pets in one river are often released into various catchments.

When crayfish are introduced into non-native bodies of water, such as the crayfish plague in Europe or the introduction of common yabby (named Cherax destructor) into drainages east of the Great Dividing Range in Australia, there is a risk of ecological damage.

Sentinel Species

The Protivin brewery present in the Czech Republic uses crayfish outfitted with sensors to detect the pulse activity or changes in their bodies in order to monitor the water purity used in their product. The creatures are kept in the fish tank, which is fed with the similar local natural source water used in their brewing. If either three or more of the crayfish have changes to their pulses, employees know that there is a change in the water and then examine the parameters.

Scientists also monitor the crayfish in the wild in natural bodies of water to study the pollutant levels out there.

Threats to Crayfish

Crayfish are susceptible to some infections such as crayfish plague and to environmental stressors, including acidification. In Europe, they are specifically threatened by the crayfish plague, which is caused by North American water mold Aphanomyces astaci. This water mold was transmitted to Europe when the North American crayfish species were introduced. Species of the genus Astacus are specifically susceptible to the infection, enabling the plague-coevolved signal crayfish (native to western North America) to invade the parts of Europe.

Acid rain may cause problems for crayfish worldwide. In whole-ecosystem experiments simulating acid rain at the Experimental Lakes Area in Canada, Ontario, crayfish populations crashed – probably due to their exoskeletons being weaker in the acidified environments.

Lobster vs. Crayfish

Crawfish and lobster are entirely two different species, although somewhat they resemble each other.

Crawfish live in fresh and brackish waters, whereas lobsters live in the saltwater oceans. The size is also different. The largest crawfish are very small lobsters.

Also, crawfish are too cheap in price and taste much better than lobsters. They are sweeter and have a better texture. Lobsters give less taste in comparison, and due to their size, they are slightly tougher. Also, crawfish are easier to cook and provide much satisfaction, more palatable to several people.