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The Yabby is a
freshwater crayfish native to Australia.
Yabbies grow well in farm dams and some commercial aquaculture
operations are extensive farm dam harvest operations
Commercial Fishing & Aquaculture Farming for Yabbies:
The Yabby is a freshwater crayfish native to
Australia. Also known as a crawchie, crawdad, craybob or even lobbie, it's all
dependent on where you come from. Yabbies as a name can refer to any number of
different crayfish species (small smooth shelled species) but as a rule it
generally refers to Cherax destructor. This species is a native of the
Murray Darling system (west of Great Divide – eastern states) and has the
broadest distribution of any species in Australia. In fact the yabby Cherax
destructor is one of the few species other than man which is increasing its
distribution across the planets surface. Unfortunately, it is an invasive
species and is becoming established along the eastern drainage of Australia in
streams that it is not endemic to. The repercussions of this and the effects to
the native crayfish species and animals that live in these streams are unknown.
Yabbies are also known as the western blue claw yabbies, basically because they
mostly have blue claws. Yabbies can be any colour blue, black, white, brown,
red, green or any combination, they will change colour to that which is most
suitable for camouflage in the wild. Yabbies grow to a maximum size of 350 gram,
however, the common large size is 120 – 150 gram. Yabbies have a life span of
only 5 – 7 years under average conditions, in the wild their life expectancy is
much shorter as they are towards the bottom of the food chain and a vast amount
of animals consume them. Some of their main predators are insect larvae, fish,
eels, turtles, birds and water rats.
Yabbiesgrow well in
farm dams and some commercial aquaculture operations are extensive farm dam
harvest operations where yabbies are just trapped from farmer’s dams. If you
have a group of farmers with lots of farm dams full of yabbies then this is a
viable option.
Generally most commercial farms are located on rural properties in specially
designed yabby ponds. Commercial yabby farms consist of large numbers of shallow
ponds designed specifically for the yabbies. This maximizes the growth and
numbers of yabbies that the pond produces. It also allows for easy management
and less costs in construction and ongoing maintenance.
Scientific Name
Cherax Species
Location in Australia
WA, QLD, NT, NSW, VIC, SA
Season
All year round
Size
300-500 carapace length *variation between sexes
Australian Species Code
00 704005
Taste, Texture
Farming and Handling of Yabbies Video (Fisheries Research
AU):
FARMING YABBIES (Source: Government of Western
Australia - Department of Fisheries)
You do
not need any permits to grow yabbies for your family and yourself, however, if
you want to sell yabbies then you will need an aquaculture permit from
your states Fisheries Department.
Spawning
The sex of yabbies can be determined externally. Females have oviducts located
at the base of the third or middle of the five pairs of legs, while male genital
papillae are at the base of the fifth pair of walking legs, nearest the tail. A
male deposits a spermatophore between the female's fourth and fifth pair of
walking legs and the female extrudes the eggs, mixes them with sperm and
attaches them to the swimmerets located under her tail.
Yabbies typically produce from 30 to 450 eggs per brood, although an average
spawning is 350 eggs. Larger females generally produce more juveniles. The eggs
hatch on the female and the juveniles are carried until they reach an advanced
stage of development and detach themselves. Eggs are incubated under the tail of
the female yabby and take between 19 and 40 days to hatch, depending on water
temperature. After the young leave the female she is capable of spawning again
immediately if environmental conditions are suitable.
In cold parts of their eastern Australian native range yabbies spawn annually
during the summer months. The cue for development of eggs inside the female is
longer day lengths and for spawning, higher water temperatures. When water
temperature is above 15 degrees Celsius, yabbies spawn from early spring to mid
summer. However, if the water temperature remains between 18 degrees and 20
degrees Celsius with a long artificial day length of 14 hours, they are capable
of spawning repeatedly up to five times through a year.
Female yabbies are sexually mature at a very small size and early age - at 20
grams and less than one year old. In the South-West of Western Australia, young
may be released in December and again in February. Unfortunately, this prolific
breeding has major disadvantages for aquaculture because it results in
over-crowding and stunting of growth in farm dam populations. Clearly, there is
no need to have a hatchery for yabbies. A hybrid between two yabby species has
been discovered from which all progeny are males. This simple technique can be
used to prevent reproduction in carefully stocked ponds. Because male yabbies
grow faster than female yabbies, the hybrid-cross also results in larger and
therefore more valuable animals. It is also possible to produce sterile yabbies
by hybridising a number of yabby species and these may also have potential for
controlling reproduction in ponds and dams.
Culture Environment
Yabbies are adapted to a higher temperature range than marron and thrive in the
warmer, drier inland regions. Yabbies do not grow at winter water temperatures
below 15 degrees Celsius and grow best at 28 degrees Celsius. Growth ceases at
over 34 degrees Celsius, and mortalities start to occur at 36 degrees Celsius.
Growth of yabbies ceases at salinities above eight parts per thousand (ppt),
equal to about one quarter seawater. Although yabbies tolerate higher
salinities, they become stressed at salinities over one-third seawater, with
mortalities occurring at levels above half seawater. Yabbies are hardier under
stagnant water conditions than marron and can tolerate dissolved oxygen levels
lower than one part per million (pp) and can survive for a short time at zero
oxygen. However, feeding activity and hence good growth are dependent upon
healthy, well oxygenated water conditions. Excessive run-off of sheep manure
should be avoided as it leads to depressed oxygen levels. This can be achieved
by constructing contour banks leading to sediment traps at the mouth of the dam.
Farm dams do not have a piped water supply and are necessarily deep (four
metres) to retain some water over summer. Most of the light and heat of sunlight
are absorbed close to the surface in these muddy dams, so that water below about
one metre is colder and heavier than surface water - this is called layering or
stratification effect. This cold, deeper water becomes deoxygenated, resulting
in the yabbies being forced to crowd in the shallows close to the banks, making
them more vulnerable to predators.
Extensive pond or dam production of yabbies can yield 400-690 kg per hectare of
water area (kg/ha). However, many of these yabbies are below market size due to
uncontrolled breeding. Farm dams cannot be readily drained for (i) efficient
harvesting during winter; (ii) stock control against excessive breeding; or
(iii) cleaning out of the bottom mud when the sediments become over enriched.
Harvesting yabbies from dams by actively hauling a seine net is damaging to the
animals physically and may result in bacterial infection from mud stirred up
from the bottom. However, better feeding practices and monosex stocking of male
and female yabbies are leading to much better yields, larger yabbies and better
prices. Fortunately Cherax albidus has been shown to be relatively
non-destructive in farm dams as it constructs fairly shallow burrows in
comparison to the aptly names central Australian yabby species Cherax
destructor.
The use of purpose-built adjacent ponds at a site favourable for more intensive
crayfish farming has a number of advantages over widely spread and isolated farm
dams. Unfortunately, at current market prices, the level of investment that is
required to build and manage commercial ponds is rarely economic for yabbies,
unlike their larger relative marron (Cherax tenuimanus and Cherax
cainii) which have a much higher market price.
When harvested from farm dams, trapped yabbies need to be gill washed in clean
water immediately on the dam bank and subsequently kept cool in a moist
atmosphere. For marketing, a processor must purge, or depurate, the yabbies in
clean water to empty food from the digestive tract in the tail (the dark vein)
to improve the flavour of the flesh and to prevent stress during transport due
to fecal wastes in the carton.
Diet
Yabbies, like most crayfish, are detritus feeders. Consequently, while
supplementary feeding is essential for higher than natural crayfish production,
crayfish ake up for the deficiencies of essential micronutrients in the
artificial feed by also eating natural food in the pond.
A variety of low cost feeds and feed rates have been evaluated with the most
promising results coming from cheap freshwater crayfish pellets fed at the rate
of 5-10g/m2/week. Nutrient leachates, from the artificial feed, enhance the
amount of natural food in a dam. While some farmers feed yabbies lupins,
commercial marron pellets give much better results. The major, and very
widespread, problem in yabby ponds has been underfeeding. Improving feed quality
and increasing feed rates can improve yabby growth by 85 per cent.
Growth
Yabbies can reach a maximum size of 320 grams and these large yabbies are males.
Females are greatly suppressed in growth by the diversion of food energy into
spawning. As size increases, yabby claws increase relatively more in size than
the rest of the body and they are massive in larger males over 100 grams.
Although individual growth of yabbies is temperature and density dependent.
Consequently the uncontrolled breeding of yabbies in farm dams not only produces
many undersize animals, but also affects the subsequent growth and survival of
the parent stock.
Regular trapping of dams is vital to control density so that optimum growth can
be achieved. But, farmers must be careful that they do not harvest all the
fastest growing yabbies from their dam and leave the slower growing animals to
become the broodstock for future generations, otherwise stunting will occur.
At the onset of their early maturity and first spawning, growth of female
yabbies declines markedly and is zero while they spawn over spring and summer.
Monosex culture, by separating male and female yabbies, gives better growth for
both sexes and results in a 70 per cent increase in grow income.
The tail meat recovered from headed and shelled yabbies is 15 to 20 per cent of
the total body weight (the basis for sale of crayfish), and is lower than 31 per
cent obtained from marron. They also fetch a much lower price than marron but
can be produced with very inexpensive technology.
Yabby Health Issues
For the protection of Western Australian native crayfish stock (gilgies, koonacs
and marron), live crayfish may not be brought into this State from other
Australian States and Territories. To preserve the disease status of existing
yabby stocks in Western Australia, further unregulated introductions of yabbies
into this State are not permitted.
The microsporidian parasite Thelohania affects yabby and other freshwater
crayfish populations in eastern states and has unfortunately become established
in Western Australia.
Yabbies and all other Australian crayfish are extremely susceptible to the
"crayfish plague" of the northern hemisphere (a fungal disease Aphanomyces
astaci, found on American crayfish), which has devastated Europe's native
crayfish populations. To guard against plague, the importation into Australia
of any species of live foreign crayfish for whatever purpose, is not permitted.
Surface fouling on yabbies by ectocommensals, such as the protozoan Epistylis
and the platyhelminth (flat worm) Temnocephala, although rarely harmful
to the animals unless in extremely high densities, lowers the market appearance
of affected individuals. These so-called epibionts are symptomatic of waters
which are over enriched with nutrients. A virus that affects a small percentage
of yabbies has also been discovered but, as with these other diseases or
ectocommensals, it poses no threat to humans.
Economics of Production
The establishment costs for farm dam production of yabbies is very low. As most
farmers already have their dams for watering stock, the only equipment required
are traps to catch the yabbies and containers for gill flushing and
transportation. Alternatively, farmers may elect to have commercial harvesters
trap their yabbies and receive a percentage of the crop value. Commercial
semi-intensive pond production is much more expensive with set up and operating
costs similar to those of a marron farm.
A case study of the economics of harvesting yabbies from a farmer's dams was
conducted (1996) and in that year the farmer produced marketable yabbies which
grossed $19,000. The study demonstrated that the farmer, who had 46 dams on the
property, incurred the costs shown below. After removing working costs from the
$19,000 gross income for 1996 the farmer received $13,504 for the year. The
farmer spent 360 hours, or approximately 7 hours per week, on harvesting and
feeding the yabby dams which provided an equivalent return of $37.51/hour of
labour.
The Yabby is a freshwater crayfish native to
Australia. Also known as a crawchie, crawdad, craybob or even lobbie, it's all
dependent on where you come from. Yabbies as a name can refer to any number of
different crayfish species (small smooth shelled species) but as a rule it
generally refers to Cherax destructor. This species is a native of the
Murray Darling system (west of Great Divide – eastern states) and has the
broadest distribution of any species in Australia. In fact the yabby Cherax
destructor is one of the few species other than man which is increasing its
distribution across the planets surface. Unfortunately, it is an invasive
species and is becoming established along the eastern drainage of Australia in
streams that it is not endemic to. The repercussions of this and the effects to
the native crayfish species and animals that live in these streams are unknown.
