The Yabby

Definition; yabby / l jæbi /, n 1. an Australian freshwater crayfish, of genus Cherax. -v.i. 2. to catch yabbies. Also, yabbie. - yabbying, n. (The Concise Macquarie Dictionary)

This is a good opportunity to note the spelling used. In many parts of the world, Yabbie is the common name, but in Australia Yabby is the preferred option. In both cases however, Yabbies is used for the plural and they are always delicious. (Even my spell checker gets this one right for a change)

Biology

 
Phylum: ARTHROPODA
Subphylum: CRUSTACEA
Class: MALACOSTRACA
Order: DECAPODA
Infra-order: ASTACIDEA
Family: PARASTACIDAE
Genus: CHERAX

 

Four of the better known Australian yabbies include:-
GENUS SCIENTIFIC NAME COMMON NAME DISTRIBUTION
Cherax destructor Blue Claw Throughout AUS
Cherax albidus Blue Pearl VIC, WA
Cherax quadricarinatus Red Claw QLD, NSW
Cherax tenuimanus Marron WA

 

 

Habitat

The yabby is capable of living in virtually any body of fresh water including rivers, streams, dams and even some temporary waters. Yabbies actively burrow into dam walls and are very hardy creatures. They are able to withstand poor water quality, fluctuating temperatures and long periods of drought. If a particular watercourse dries up, yabbies burrow deep into the bottom until they reach moist soil, and remain there until the watercourse fills once again. They can remain this way for many months, or even years.

Yabbies are known as detritus feeders (rotting vegetable and animal matter); they are omnivorous although prefer a vegetarian diet. The yabby is not averse to attacking and eating its own kind, especially when the prey yabby is smaller, or soft after shedding its shell

To live, the yabby does not require to be immersed in water. If its gills are kept wet it can absorb oxygen from the air and can survive for many months.

To breed however, the yabby must be completely immersed in water.

Environmental Factors

Some environmental factors to consider when farming yabbies are: -

DO (Dissolved oxygen)
Water should contain over 4ppm (parts per million) of DO, or roughly 40% saturation

TEMP
Adult yabbies can tolerate quite a large temperature range of between 1ºC and 35ºC. Juvenile yabbies do not survive over 30ºC and the preferred temperature is between 15ºC and 26ºC

pH
Yabbies prefer alkaline water (pH 7.5 to 10), rarely are yabbies found in acidic water (pH below 7) as this inhibits their metabolism and respiration rate.

SALINITY
A salinity level of up to 12ppt (parts per thousand) will not affect yabbies but they will die at levels of 25ppt.

CHLORINE
Low levels of chlorine do not seem to affect adult yabbies, however juveniles do suffer at higher levels and start to die off.

Growth

Like all crustaceans, yabbies must "moult", or shed their shell (external skeleton) to grow. Growth of this kind is not continuous; juveniles moult every few days but far less often as they age. A two year old yabby may moult only once a year. Growth also depends upon water temperature, available food and population density. A female yabby never grows to the size of an adult male. The average yabby caught in dams is 7 to 10cm long and weighing 20 to 60gms.

Disease

In natural populations causes of death include predators, cannibalism, fishing, injury, starvation, disease and old age. Diseases such as the European Crayfish Plague (Aphanomyces) have devastated European stocks and reached British native stocks in 1986. Australia is the only continent to be Crayfish Plague free.

Porcelain disease (or White Tail disease) can also occur in the yabby, caused by a single celled microscopic animal, the microsporidian Thelophania. The disease can easily be detected in its late stages, when the underside of the tail turns white and the walking legs often become rigid and splayed. It is invariably fatal and seems to be transmitted by cannibalism of dead or dying yabbies that have the disease. This disease is not harmful to humans, and is present in possibly 5% of natural crayfish populations.

Themnocephalid flatworms are 1 to 110mm long leech-like animals, and their eggs are laid on the soft under surfaces of the crayfish. These worms are not true parasites but commensals because they feed upon particles of food scattered in the water while the crayfish is eating. They are not actively harmful to the crayfish.

Home Aquarium Pets

Yabbies are entertaining aquarium pets and very easy to keep.

Two large (100gm) or four small (30gm) yabbies can be kept quite happily in a 4-foot aquarium by giving them enough shelter to hide when moulting, feeding them regularly and supplying a filtered/oxygenated environment. The yabby can live for months without eating at all so it's better to under-feed than over-feed. This will help to keep the environment free of algae. Yabbies breed readily. No special food is required for the juveniles as they will feed on scraps missed by the mother. Extra shelter is required as other yabbies, and even mothers eat the juveniles. It is also important to keep the water level below the top of the tank, and the lid on at all times so that the yabbies do not climb up the air hose and escape.

Preparation and Cooking

There are many edible parts to the yabby. The tail and the claw meat (about 40% of the total body weight) form the bulk of the edible flesh.

The 'mustard' is the soft, orange-brown liver found in the carapace (main shell). It has a mustard flavour and connoisseurs relish it spread over the tail meat. The 'coral' is the developing ovary or egg sac, found in the carapace of the female. This turns red on cooking and is quite tasty alone, or beaten into sauces.

There is an abundance of other information available including:

  • New South Wales Fisheries
  • Western Australia Fisheries
  • Native Fish Australia
  • CSIRO Animal Production, South Australia