Paranephrops is a genus of freshwater crayfish found only in New Zealand. They are known by the English common names freshwater crayfish and koura, the latter from their Māori name of kōura.

The two species are:

Both species are a traditional food for Māori, and a small koura aquaculture industry supplies the restaurant market.

The northern koura (P. planifrons) reaches lengths of about 70 mm (2.8 in), whereas the southern koura (P. zealandicus) is slightly larger – 80 mm (3.1 in) – 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 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.

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, and mayflies are the main food source. Juvenile koura require higher amounts of protein 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 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.

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 5–10 metres (16–33 ft). In streams, koura take cover on the bottom beneath fallen leaf litter, fallen logs, and tree roots and undercut banks. Tree fern 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.

Eels, perch, catfish, and trout are the major aquatic predators of koura. Terrestrial predators include rats, kingfishers, shags, scaup, stoats, and kiwi. Shag populations in the Rotorua lakes 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 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 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.

Koura, like all crustaceans, moult their exoskeletons to increase in size. During moulting, the carapace becomes soft with calcium 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 gastroliths 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 in water for temperate species of koura has been suggested as sufficient to support exoskeleton hardening.