Southern Koura

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 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.

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.

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 dish. Koura are harvestable once larger than 100 mm (3.9 in) 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 200 m2 (2,200 sq ft) 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 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 15–18 °C (59–64 °F), 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. …