Crayfish in the context of "Freshwater prawn farming"

Crustaceans (from Latin word "crustacea" meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (/krəˈsteɪʃə/), a large, diverse group of mainly aquatic arthropods including the more familiar decapods (shrimps, prawns, crabs, lobsters and crayfish), seed shrimps, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, opossum shrimps, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods (insects and entognathans) emerged deep in the crustacean group, with the completed pan-group referred to as Pancrustacea. The three classes Cephalocarida, Branchiopoda and Remipedia are more closely related to the hexapods than they are to any of the other crustaceans (oligostracans and multicrustaceans).

The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm (0.004 in), to the Japanese spider crab with a leg span of up to 3.8 m (12.5 ft) and a mass of 20 kg (44 lb). Like other arthropods, crustaceans have an exoskeleton, which they moult to grow. They are distinguished from other groups of arthropods, such as insects, myriapods and chelicerates, by the possession of biramous (two-parted) limbs, and by their larval forms, such as the nauplius stage of branchiopods and copepods.

Lake Sevan (Armenian: Սևանա լիճ, romanized: Sevana lich) is the largest body of water in both Armenia and the Caucasus region. It is one of the largest freshwater high-altitude (alpine) lakes in Eurasia. The lake is situated in Gegharkunik Province, at an altitude of 1,900 m (6,234 ft) above sea level. The total surface area of its basin is about 5,000 km (1,900 sq mi), which makes up 1⁄6 of Armenia's territory. The lake itself is 1,242 km (480 sq mi), and the volume is 32.8 km (7.9 cu mi). It is fed by 28 rivers and streams. Only 10% of the incoming water is drained by the Hrazdan River, while the remaining 90% evaporates.

Sevan has significant economic, cultural, and recreational value. Its sole major island (now a peninsula) is home to a medieval monastery. The lake provides some 90% of the fish and 80% of the crayfish catch of Armenia.

Cancer (♋︎; Ancient Greek: Καρκίνος, romanized: Karkínos, lit. 'crab', Latin for the "Crab") is the fourth astrological sign in the zodiac, originating from the constellation of Cancer. It spans from 90° to 120° celestial longitude. Under the tropical zodiac, the Sun transits this area between approximately June 22 and July 23.

In astrology, Cancer is the cardinal sign of the Water trigon, which is made up of Cancer, Pisces, and Scorpio. It is one of the six negative signs, and its ruling planet is the Moon. Though some depictions of Cancer feature a lobster, crayfish, scarab beetle or a turtle, the sign is most often represented by the crab, based on the Karkinos. Cancer's opposite sign is Capricorn.

A bottom feeder is an aquatic animal that feeds on or near the bottom of a body of water. Biologists often use the terms benthos—particularly for invertebrates such as shellfish, crabs, crayfish, sea anemones, starfish, snails, bristleworms and sea cucumbers—and benthivore or benthivorous, for fish and invertebrates that feed on material from the bottom. However the term benthos includes all aquatic life that lives on or near the bottom, which means it also includes non-animals, such as plants and algae. Biologists also use specific terms that refer to bottom feeding fish, such as demersal fish, groundfish, benthic fish and benthopelagic fish. Examples of bottom feeding fish species groups are flatfish (halibut, flounder, plaice, sole), eels, cod, haddock, bass, carp, grouper, bream (snapper) and some species of catfish and sharks.

In ecology, a cascade effect is a series of secondary extinctions that are triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic (dependent on the key species in some way), or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al. showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase (ecological release) of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area. If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss. Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.

A lobster trap or lobster pot is a portable trap that traps lobsters or crayfish and is used in lobster fishing. In Scotland (chiefly in the north), the word creel was used to refer to a device used to catch lobsters and other crustaceans. A lobster trap can hold several lobsters. Lobster traps can be constructed of wire and wood, metal and netting, or rigid plastic. An opening permits the lobster to enter a tunnel of netting or other one-way device. Pots are sometimes constructed in two parts, called the "chamber" or "kitchen", where there is bait, and exits into the "parlor", which prevents escape. Lobster pots are usually dropped to the sea floor, one or more at a time, sometimes up to 40 or more, and are marked by a buoy so they can be picked up later.