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''Paranephrops'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...
found only in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
. They are known by the English common names freshwater crayfish and koura, the latter from their
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the C ...
name of ''kōura''. The two species are the northern koura, ''
Paranephrops planifrons ''Paranephrops planifrons'' is a species of southern crawfish in the family Parastacidae. It is found in New Zealand. ''P. planifrons'' is one of two indigenous species of freshwater crayfish found in New Zealand. They are more commonly found in ...
'', found mainly in the
North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...
, but also in
Marlborough Marlborough may refer to: Places United Kingdom * Marlborough, Wiltshire, England ** Marlborough College, public school * Marlborough School, Woodstock in Oxfordshire, England * The Marlborough Science Academy in Hertfordshire, England Austral ...
,
Nelson Nelson may refer to: Arts and entertainment * ''Nelson'' (1918 film), a historical film directed by Maurice Elvey * ''Nelson'' (1926 film), a historical film directed by Walter Summers * ''Nelson'' (opera), an opera by Lennox Berkeley to a lib ...
, and the
West Coast West Coast or west coast may refer to: Geography Australia * Western Australia *Regions of South Australia#Weather forecasting, West Coast of South Australia * West Coast, Tasmania **West Coast Range, mountain range in the region Canada * Britis ...
of the
South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...
, and the southern koura, ''
Paranephrops zealandicus ''Paranephrops zealandicus'' is a species of southern crawfish in the family Parastacidae. It is found in New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmass ...
'', found only in the eastern and southern of the South Island and on
Stewart Island/Rakiura Stewart Island ( mi, Rakiura, ' glowing skies', officially Stewart Island / Rakiura) is New Zealand's third-largest island, located south of the South Island, across the Foveaux Strait. It is a roughly triangular island with a total land ar ...
. Both species are a traditional food for
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the C ...
, and a small koura aquaculture industry supplies the restaurant market.


Description

The northern koura (''P. planifrons'') reaches lengths of about , whereas the southern koura (''P. zealandicus'') is slightly larger – – with relatively shorter antennae. Their first pair of legs ( chelipeds) are pincers used for scavenging food and warding off predators or other koura. The chelipeds in ''P. zealandicus'' are much hairier at their tips than those of ''P. planifrons.'' The four pairs of well-developed walking legs are used for most movement, but the
pleopods The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in variou ...
are small and no use for swimming; when alarmed, koura can flick their tails forward violently to propel themselves backwards at speed. They can be sexed by looking at their underside; males have a pair of gonads that protrude from the base of the fourth pair of legs, while females have holes at the base of the second pair of legs.


Ecology


Diet

Koura in natural populations are omnivorous scavengers, consuming a variety of foods, with animal protein contributing the most to growth. Invertebrates including aquatic snails,
chironomids The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many species ...
, and
mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the orde ...
are the main food source. Juvenile koura require higher amounts of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
in their diet than adults due to greater growth rate demands with invertebrates forming the bulk of their diet. Koura in lakes have been shown to feed predominantly in the
littoral zone The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...
where food availability is greatest. Feeding in the littoral zone may reflect diel movement with koura moving to deeper and darker parts of lakes to avoid predation during daylight hours and moving to the littoral zone at night to feed.


Habitat

Koura occupy freshwater lakes, streams, rivers, and swamps, in mud or gravel substrates. Koura are nocturnal, moving into shallower water at night and deeper water column during the day. During daytime, they find shelter under rocks, debris such as cans and bottles, and vegetation. In soft sediments they may also excavate burrows or fan shaped depressions, in Lake Rotoiti at depths of . In streams, koura take cover on the bottom beneath fallen leaf litter, fallen logs, and tree roots and undercut banks.
Tree fern The tree ferns are arborescent (tree-like) ferns that grow with a trunk elevating the fronds above ground level, making them trees. Many extant tree ferns are members of the order Cyatheales, to which belong the families Cyatheaceae (scaly tree ...
roots that project into the stream are thought to provide excellent cover for juveniles. Fossil evidence of Paranephrops in Pleistocene sediment demonstrate occurrence in or near marginal-marine habitat, unfortunately there is little published literature about occurrences of fossilized Paranephrops.


Predators, cannibalism and disease

Eels Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
,
perch Perch is a common name for fish of the genus ''Perca'', freshwater gamefish belonging to the family Percidae. The perch, of which three species occur in different geographical areas, lend their name to a large order of vertebrates: the Percif ...
,
catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...
, and
trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...
are the major aquatic predators of koura. Terrestrial predators include rats,
kingfishers Kingfishers are a family, the Alcedinidae, of small to medium-sized, brightly colored birds in the order Coraciiformes. They have a cosmopolitan distribution, with most species found in the tropical regions of Africa, Asia, and Oceania, ...
, shags, scaup,
stoat The stoat (''Mustela erminea''), also known as the Eurasian ermine, Beringian ermine and ermine, is a mustelid native to Eurasia and the northern portions of North America. Because of its wide circumpolar distribution, it is listed as Least Conc ...
s, and
kiwi Kiwi most commonly refers to: * Kiwi (bird), a flightless bird native to New Zealand * Kiwi (nickname), a nickname for New Zealanders * Kiwifruit, an edible berry * Kiwi dollar or New Zealand dollar, a unit of currency Kiwi or KIWI may also refe ...
. Shag populations in the
Rotorua lakes Rotorua Lakes District or Rotorua District is a territorial authority district in the North Island of New Zealand. It has one urban area of significant size, the city of Rotorua. The district is governed by Rotorua Lakes Council, which is headqu ...
district in the North Island of New Zealand have been shown to feed on koura as the bulk of their diet. Predation on koura by trout is thought to be restricted to larger adult trout. Streams and lakes with established populations of trout have been shown to affect koura abundance.
Cannibalism Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, b ...
in koura is most likely to occur when koura are sick or moulting. Cannibalism can be a greater problem in high-density situations where competition for shelter and territory is greatest. Juvenile koura can be consumed whole by larger koura, and this presents problems for
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
in ensuring continuity of intergenerational growth. Koura use their chelae for both attack and defence, and when one limb is lost, the koura will divert energy for overall growth to restoring the lost limb. The only disease known to seriously affect koura is "white tail disease" caused by the microsporidian parasite '' Thelohania contejeani''. This parasite causes degeneration of striated muscle in the tail area, which turns the tail a pale white colour and correspondingly leads to death soon after.


Growth

Koura, like all crustaceans,
moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
their
exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...
s to increase in size. During moulting, the
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
becomes soft with
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
being resorbed and the remaining outer shell shed. The new carapace forms underneath, where it takes a number of days to harden. Calcium for this new outer shell comes from
gastrolith A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In othe ...
s that line the stomach wall of the koura, and these produce around 10–20% of the calcium needs for exoskeleton production. The gastroliths drop into the koura's foregut, where they are broken down to allow the adsorption of calcium. After moulting, the demand for calcium to harden the exoskeleton is high, and this demand is met in part by the koura eating its discarded exoskeleton. The remaining calcium required to completely harden the exoskeleton is achieved by absorption from the water. A lower limit of 5 mg/L of
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
in water for temperate species of koura has been suggested as sufficient to support exoskeleton hardening. Water temperature and calcium concentrations are thought to be the key variables determining koura growth rates. ''P. zealandicus'' has high survivability (>80%) rates below , but temperatures above this correlate with lower rates of survivability. Higher death rates are thought to be associated with increased activity of koura at higher temperatures. Greater activity by koura increases cannibalistic behavior, and increased activity may also affect water quality with the greater production of
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
as a waste product. Survival of koura also increases with higher calcium concentrations in the water, and this is thought to be in part due to a lower incidence of moulting-related deaths and decreased risk from predation. A calcium concentration value of 20–30 mg/L in water is thought to be ideal for maintaining koura growth and survivability in aquaculture setups.


Reproduction

The female carries 20–200
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
under the side flaps of her abdomen, where they take 3–4 months to hatch. Over this time, male sperm production corresponds with females' reproductivity. Once hatched, juvenile koura cling to their mother's abdomen using their pincers to attach until they have reached a length of . At this stage, they resemble adult koura in appearance, having undergone two moults. In Lake Rotoiti in the central North Island of New Zealand, the main breeding period occurs between April and July (autumn–winter), with a second breeding period occurring from October–January (spring–summer). The total breeding length time from peak egg laying to the release of juveniles is estimated to be 28 weeks for the autumn–winter period and 19–20 weeks in spring–summer breeding groups. This difference is attributed to warmer temperatures speeding up the egg development process. In stream populations, this growth period has been shown to take around 25–26 weeks in ''P. planifrons'', and up to 60 weeks for ''P. zealandicus'' in Otago streams.


Aquaculture

Farming of koura is currently undertaken by a small number of companies within New Zealand. Sweet Koura Enterprises Ltd and New Zealand Clearwater Crayfish Ltd are two such operators. Koura is sold solely to the high-end restaurant trade, where they are commonly eaten as an
entrée An entrée (, ; ) in modern French table service and that of much of the English-speaking world (apart from the United States and parts of Canada) is a dish served before the main course of a meal. Outside North America, it is generally synony ...
dish. Koura are harvestable once larger than in total length, which can take 2–5 years in ''P. planifrons.'' Sweet Koura Enterprises Ltd, located in Central Otago, within the South Island of New Zealand, farm ''P. zealandicus'' in artificial ponds around in size. These ponds attempt to replicate the natural environment where ''P. zealandicus'' grows. Water supplied to the growing ponds is sourced from an
aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
and is artificially aerated. The temperature of the water is controlled to reflect the seasonal temperature variations that would be expected in the natural environment. The optimal temperature for growth in these ponds is achieved at , with ''P. zealandicus'' sensitive to rapid temperature changes. The natural biological life in a pond can support 3–4 koura per m2. Additional feed in the form of fish-based pellets is supplied to koura to support growth; this feed has been altered to reflect the lower-protein, higher-calcium nutritional requirements of koura. Overstocking of crayfish can lead to higher rates of mortality, which is associated with higher rates of cannibalism and increased competition for shelter and food. New Zealand Clearwater Crayfish Ltd farm grows the northern koura species ''P. planifrons'' using a gravity-fed system with pond culture and raceways. A key step in this koura farm is the depuration of koura in clean running water without food for up to 2 days to purge the gut cavity. This enables the tail to be presented as an appealing white flesh to the consumer. To breed koura in aquaculture a ratio of one male to five females is suggested during the mating periods, with koura removed and placed in separate tanks according to the life stage once hatched. The creation of artificial habitat in ponds may support koura survival. Plastic containers, tyres, plastic piping, and bottles are all possible habits for koura to occupy when being grown in ponds. The suggested depth for ponds used to farm ''P. zealandicus'' is . A number of environmental challenges exist for koura farmers in ensuring optimum growth and survivability of stock. Environmental contamination of fresh water supplied to ponds from other land use activities, such as livestock farming, can affect survival. Other risks come from the introduction into the ponds of predators such as carp, eels, and birds; however, these can be controlled by steps such as placing netting across pond surfaces.
Algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...
s creating anoxic conditions and cannibalism caused by high-density stocking of ponds are also challenges to koura farmers. The outlook for the growth of koura aquaculture in the New Zealand domestic setting may be positive, with the potential for increasing demand in the restaurant and tourism fields. Export of koura to the international market may offer less potential due to competition from other established freshwater crayfish species such as the red swamp crayfish ''
Procambarus clarkii ''Procambarus clarkii'', known variously as the red swamp crayfish, Louisiana crawfish or mudbug, is a species of cambarid crayfish native to freshwater bodies of northern Mexico, and southern and southeastern United States, but also introduc ...
'', of which the United States and China annually consume 34,000 tonnes and 88,000 tonnes, respectively.


References


Further reading

* *


External links

*Koura or freshwater crayfish discussed on RNZ ''
Critter of the Week ''Critter of the Week'' is a weekly RNZ National programme about endangered and neglected native plants and animals of New Zealand. Beginning in 2015, ''Critter of the Week'' is an approximately 15-minute discussion between Nicola Toki of the ...
''
20 November 2015
{{Taxonbar, from=Q4473734 Crustacean genera Freshwater crustaceans of New Zealand Edible crustaceans Parastacidae Taxa named by Adam White (zoologist) New Zealand seafood Māori cuisine