The development of a nutritionally complete artificial diet for yabbies is difficult and although progress is being made, has not yet been accomplished (Jones 1996). Yabbies, like most crayfish, are detritus feeders. Consequently, while supplementary feeding is essential for higher than natural crayfish production, crayfish make up for the deficiencies of essential micronutrients in the artificial feed by also eating natural food in the pond.
Nutrient leachates from the artificial feed, enhance the amount of natural food in a dam. Food Conversion Ratios (FCR's) of 4-5:1 have been returned when feeding yabbies on lucerne pellets, but many farmers use lupins even though commercial marron pellets give better results.
The major, and very widespread, problem in yabby ponds has been underfeeding. 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 (Lawrence et al. 1998).
Yabbies can reach a maximum size of 320g 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 large males over 100 g.
Although individual growth, as in other crayfish, is always highly variable in yabbies (Mills 1983), the minimum market size of 30 g can be produced in less than six months.
As in marron, growth of yabbies is temperature and density dependent (Mills 1983). 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.
During the first few months of their first year, yabbies attain a larger size than do marron. 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 (Morrissy & Cassells 1992, Geddes and Smallridge 1993).
Monosex culture, by separating male and female yabbies, gives better growth for both sexes and results in a 70 per cent increase in gross income. The equivalent difference for marron, in current trials, is less dramatic.The tail meat recovered from headed and shelled yabbies is 15 - 20 per cent of the total body weight (the basis for sale of crayfish), and is lower than the 31 per cent obtained from marron (Morrissy et al. 1990).
They also fetch a much lower price than marron but can be produced with very inexpensive technology.