Paranephrops

Paranephrops is a genus of freshwater crayfish found only in New Zealand. They are known by the English common names freshwater crayfish^[1] and koura,^[2] the latter from their Māori name of kōura.^[1] The two species are the northern koura, Paranephrops planifrons, found mainly in the North Island, but also in Marlborough, Nelson, and the West Coast of the South Island, and the southern koura, Paranephrops zealandicus, found only in the eastern and southern of the South Island and on Stewart Island/Rakiura. 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.^[3] 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.^[3]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.^[4]

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).^[3] 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.^[4] 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.^[5]

Paranephrops forms much of the diet of the black shag in the Rotorua lakes

Northern crayfish, P. planifrons

Northern koura, P. planifrons