New
Zealand Clearwater Crayfish (Koura) Ltd
New
Zealand Clearwater Crayfish (Koura) Ltd (NZCC) is a private
company established in 1996 by Peter Wilhelmus and David
Smythe to farm the North Island species (Paranephrops planifrons)
of New Zealand freshwater crayfish known as koura.
This
new pioneering venture in New Zealand is still very much
in the development stage but minor sales of live koura have
been made since late 1999.
The
NZCC koura farm is part of an organic freshwater aquaculture
complex based on a small mixed sex salmon farm. It is located
in Wairau valley about 35km from Blenheim.
The
farm was only the second in New Zealand to be established
and market farmed koura. The first being near Alexandra.
There
was no information or existing practical experience to build
upon so the farm has been developed by the partners through
hard work, trial and error, and reading literature from
Australia, USA and Europe to glean ideas. David Smythe has
visited yabbie farms in Australia.
After
initial aquarium trials in 1993 and 1994, field trials began
in 1995 and farm construction began in March 1997 with a
broodstock pond of some 100m² and two races totalling
80m in length and 5m wide.
Koura broodstock pond and first two growing-on
races 22 November 1997
Four more races totaling 485m were built in March 1998 and
a small hatchery comprising 12 tanks was built in April
1998 adapted from earlier trials.
Peter
assesses the new hatchery
In
mid 1999 the hatchery was tripled in size and now houses
360 females. Three races each 100m long were built in June
2000 and another 200m were constructed in 2001 and the remainder
will be constructed in 2002 which will bring the total length
of growing-on races in the farm to over 1500m.
Water
is diverted from the Ormond Aquaculture Ltd organic salmon
farm settling pond via a rock screen and head race to the
growing on races. The Koura environment is managed to achieve
as closely as possible natural conditions but with considerable
enhancement such as eliminating predators from all sources
and providing abundant natural cover and a supplementary
diet.
Berried
female about 120gm and 140mm TL with about 350 eggs
Broodstock
either mate in the broodstock pond or are collected and
selectively mated in tanks. Selective mating is experimental
but showing very good results. Berried females are collected
from the broodstock pond 3 to 4 months after mating and
transferred to the hatchery. Females selectively mated are
placed in the hatchery as soon as the fertilised eggs are
cemented to the pleopods.
One
of the Founding Fathers
When
all the hatchlings have left the female she is returned
to the broodstock pond and the hatchlings remain in the
hatchery until about 10 to 15mm overall length (TL) then
transferred to a growing-on race. During that time they
have undergone at least four if not five molts and the shell
has 'hardened up so that the translucent effect of the baby
hatchlings has disappeared and they have taken on a brown-faun
colouring.
We
have often been asked by students if the colour of koura
is influenced by their surroundings or container they are
kept in. We have not been able to identify any colour change
in either adults, babies, or juveniles that is attributable
to the colour of the container. The only colour change we
have seen is the natural change from translucent baby to
brown-faun juvenile.
Minimum
marketable size of about 100mm TL and 45 to 55gms weight
is achieved in 20 months to 2 years while up to 105-115mm
TL and 90 to 110 gm is achieved in about 2 &1/2 years.
Larger size Koura of around 130 to 150 mm TL and 120+ gms
have grown in about 3 years. It is too early to be certain
about actual or predicted growth rates but these figures
are indicative of what is being achieved. Results are very
encouraging as to growth and fertility with berried females
having been produced at 15 months age.
Pincers
on left: 160mm - 6 males with 3 females on right end.
Size range: males 150-165 gms, females 80 - 95 gms.
Fecundity
is also improving with females carrying about 150 to 200
eggs on average. Some large selectively mated females have
had over 400 eggs.
In
August 2000 females were found mating while some were found
with eggs just hatched. This is both late (some two months)
and very early (3 months) respectively and looks promising
for possibly having a wide spread of breeding through the
year, if the trend continues. However, the timing may be
influenced by the La Nina weather pattern over New Zealand
the last three years bringing gradually warmer temperatures.
The
farm now has about 1000 breeding females, the majority of
which have been grown in the farm. This broodstock provides
the basis for continuity of supply for full commercial production.
The first rotation was initiated in February 2000 when some
35000 hatchlings were transferred from the hatchery to the
races. Provided the same or more hatchlings can be carried
to survival in the hatchery each year, an annual commercial
harvest of around 1.5 to 2T should be possible. There are
still problems to overcome. The harvest of the first full
commercial rotation is due to commence in late 2001.
The
total aquaculture complex of OAL and NZCC is a completely
GE free enterprise and in August 2000 received interim certification
by AgriQuality New Zealand as an organic freshwater salmon
and crayfish farm. Full certification ("CERTNZ")
was obtained in December 2001. It is understood that this
is the only certified organic freshwater aquaculture farm
in Australia and New Zealand.
The
directors are confident that the system developed is sustainable
and in harmony with the environment. Achieving organic certification
for both the salmon and freshwater crayfish farms is a major
achievement and bodes well for the future.
A
feature of the farm is the careful management of the environment
in which Koura thrive. A high level of natural nutrition
is promoted but supplementary feeding is essential to achieve
growth rates desirable for a commercially viable enterprise.
A
high protein organic food has been developed utilising all
solid waste from processing salmon and suitable 'waste'
fish is purchased and processed into our fish silage on
site. The fish silage is mixed with other organic products
to produce the koura food. The koura are fed every evening
if all the previous feed out has been consumed.
At this stage there is no scientific data to show feed out
rate per kg of koura or the conversion rate.
No
chemicals or hormones are used.
Koura
are harvested by trapping in 'opera house' traps, but can
be done less efficiently by dragging a scoop net through
the weed, or by draining the race and collecting Koura by
hand.
Before
sent to market the koura must be held in clean running water
without food for up to two days so that the gut line is
purged. This enables the koura to be presented with a clean
white tail meat attractive on the plate.
Koura
should be chilled in a freezer for about 3 hours before
dropping into boiling water or putting on the barbeque.
The shell will turn a bright red. Cook for about 3 minutes
then drop into a large bowl of cold water to arrest the
cooking. The cooked colour is a real stand-out in any food
preparation or presentation.
There
are several ways the cooked koura can be presented and it
is really over to the imagination of the chef. If further
cooking is to be done, such as sauté the tail meat
in garlic or herbed butter, the initial cooking time should
be 50% shorter.
One
male and five females; four showing eggs cooked on body
as 'crayfish caviar'
Pile
of male koura
Koura
tails, sautéed in butter and garlic with honey glaze
and dipping sauce
There
are many things NZCC would like to do by way of research
and development but several factors limit the immediate
prospects for serious research. The first serious project
has been the development of an electronic counter for the
hatchlings. In November 2000 NZCC received a NZ Industry
Awards Grants for this project, a very small but useful
contribution to the external costs involved. Much more needs
to be done to perfect the counter.
A
second NZIA grant was received in Dec 2001 and a second
prototype counter is under field trials.
Research
and development is on going with the hatchery to increase
survival rate of hatchlings.
