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 dish. Koura are harvestable once larger than 100 mm (3.9 in) in total length which can take between 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 of approximately 200 square metres (2,200 sq ft) in size. These ponds attempt to replicate the natural environment that P. zealandicus grow in. 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 optimum temperature for growth in these ponds is achieved at between 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 square metre. Additional feed in the form of fish based pallets are supplied to koura to support growth and 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 the northern koura species P. planifrons using a gravity fed system with pond culture and raceways for farming koura. A key step in this koura farm is the depuration of koura in clean running water without food for up to 2 days in order to purge the gut cavity. This enables the tail to be presented as an appealing white flesh to the consumer.
In order to breed koura in aquaculture a ratio of 1 male to 5 females is suggested during the mating periods with koura removed and placed in separate tanks depending of the life stage once hatched. The creation of artificial habitat in ponds may support koura survival. The use of 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 are 1.3–5.0 m (4 ft 3 in–16 ft 5 in) deep.
A number of environmental challenges exist to koura farmers in ensuring optimum growth and survivability of stock. Environmental contamination of freshwater supplied to ponds from other land use activities such as livestock farming can affect Koura survivability. 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 netting across pond surfaces. Algal blooms creating anoxic conditions and cannibalism caused by high density stocking of ponds is also a challenge to koura farmers.
The outlook for the growth of koura aquaculture in the New Zealand domestic setting may exist 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 of which the United States and China annually consume 34,000 tonnes and 88,000 tonnes respectively.
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