Stochastic dynamic model analysis of the effect of stocking density on the monosex production of male redclaw crayfish Cherax quadricarinatus reared in commercial gravel-lined ponds

The potential for commercial Australian redclaw crayfish culture is considered very significate. However, information on maximization of pond carrying capacity that provides consistent production of commercial sizes is limited. A stochastic model was used to study the dynamics of commercial male redclaw production in 2500 m(2) gravel-lined ponds with continuous aeration, when reared at 1, 2, 4, and 6 pre-adults m(-2). After 119 days, the individual weight ranged from 80.9 to 90.5 g, survival averaged 74.0%, yields varied from 0.68 to 3.2 ton ha(-1), depending on density, and the feed conversion ratio fell within the 0.75-0.87 range, indicating good production performance of male redclaw when compared with other reports. Three commercial whole-body size ranges were considered for evaluation: 40-60, 61-90 and over 90 g. The commercial category including males weighing 90 g or more was the most productive in terms of biomass, followed by the groups integrated by 61-90 and 40-60 g individuals. Production distributions inferred using the stochastic model resulted in mean yields approximating the crops in the database, with differences ranging from 0.9-7.1% and coefficient of variation values from 0.03 (1 m(-2)) to 0.81 (6 m(-2)) indicating higher uncertainty in the expected production at the highest density. The random variability of the 40-60 category and mean individual weight during rearing were the main factors affecting yields. We conclude that it is feasible to produce up to 3.2 ton ha(-l) male redclaw crayfish in gravel-lined ponds, and that the stochastic model is useful for redclaw production analysis, establishing the relationships among commercial categories from a dynamic perspective, and to identify and assess production variability.