Key Data for Keeping Yabbies

Temperature
The yabby is tolerant of high and low water temperature, and can survive 1-35℃. However, feeding and growth cease below 16℃ or above 34℃. The yabby grows normally at 20-28℃, and grows fast at 24-25℃.


Dissolved Oxygen
The yabby can tolerate very low dissolved oxygen and can survive temporally even below 1ppm. However, the water should preferably contain over 4ppm. The dissolved oxygen level above 6ppm is ideal.


Water Quality

pH
The water should be alkaline ( pH 7.5-10.5). The yabby is rarely found in acidic waters (pH below 7.0) where moulting and shell hardening problems occur.

Salinity
The Yabby can tolerate elevated salinity up to 8ppt (equal to 1/4 seawater). However, salinity level should not exceed 2ppt. The yabby survives for 48 hours in seawater, but it will die at last above 25ppt.

Hardness
The water must be hard enough (as dissolved calcium level of more than 80ppm) to maintain strength in the shell.

Heavy Metals
The yabby, being tolerant of mercury and lead, can concentrate these metals in its body without harm, and so may be caught and used for a biological indicator of environmental pollution.

Others
The yabby is susceptible to insecticides and herbicides. The juvenile is particularly affected by chlorine.


Reproduction
The yabby reaches sexual maturity when 9-10cm long (40-45g, within 16 months of hatching). Some yabbies may reach this size within 12 months. Breeding begins in spring when the water temperature reaches 15-16℃. The number of eggs per individual is 100-1000, depending upon the size of the female. The female may spawn three or more times during the breeding season from spring to autumn. The length of time taken for the eggs to hatch entirely depends on temperature. Normally it takes 19-40 days to hatch. In water temperature of 23-24℃, the eggs hatch in 3 weeks. The juvenile will leave the mother 2-3 weeks later.


Growth
At juvenile (1-2g) stocking rates of 5-10/�u, the yabby shows 50-70% survival. The yabby can be average 40-60g in 6 months above 20℃ and the growth rates will range 5-100g after 1 year. The yabby grows fast at 24-25℃ and stops growing below 16℃.


Disease

Porcelain disease (White tail disease)
This disease is caused by a single-celled animal, microspordian, Thelohania. The yabby, being an opaque or whitish blotched abdomen in the advanced phase, will die. The disease is transmitted through cannibalism of infected individuals. There is no known treatment for Thelohania. The disease may be managed by screening out and destroying animals, though the disease can not be easily detected in the early stage. There is a report in Australia that it is present in 5-10% of dams, with 5% of individuals in an affected population.

Crayfish plague
Crayfish plague caused by fungus Aphanomyces astaci and originated in the United States spread to Europe and destroyed their crayfish stocks. The fungus is not present in Australia, but it is not known whether the fungus is present in Japan or not.

Parasites
A temnocephalan or an epistylis are found on the gill or shell. They are not actively harmful to the yabby but they may cause the harm if there are too many. Temnocephalan or epistylis may be removed with salt baths. Dose: either 30 grams of salt (not table salt but sea salt or artificial sea salt) per liter of bath, for 2-3 minutes; or 10 grams per liter of bath, for 30 minutes.


Diet
The yabby is primarily detritovore and its main sources of nutrition are the microbes (including bacteria and fungi) that break down leaf matter. Best growth rates are achieved with supplementary feeding.　Pelletized diet, earthworms, maggots, water plants, cabbage leaves, carrot tops, peeled potatoes, tomatoes, etc. Coloured fruits and vegetables are good for the animal pigment (body colouring).