Determining Suitable Thermal Regimes for Early Instar Redclaw Juveniles, Cherax quadricarinatus (von Martens, 1868) (Decapoda, Parastacidae), for a Proposed Nursery Phase

Abstract

Abstract Modern, intensified aquaculture typically involves three production phases; hatchery, nursery, and grow-out. For redclaw crayfish aquaculture however, such delineation has been ill-defined. Farming of redclaw was initiated based on the putative beneficial physical and biological attributes of the species, which suggested production methods would be relatively simple. The simple approach proved to be inefficient and only partially effective, which hindered industry development. Hatchery technology now exists to supply seed stock for grow-out, but hatchery production is variable, and the performance of hatchery reared juveniles is inconsistent. A nursery phase has been proposed between hatchery production and grow-out of approximately 3 weeks duration, sufficient to allow 2 or more moults. An important primary parameter in the proposed nursery phase is the thermal regime that will support optimum survival and growth. This study quantified the effect of temperature on the growth and survival of redclaw juveniles for a 22-day nursery phase. Temperature had a statistically significant effect on the survival of juveniles, whereby, the high temperatures were associated with high mortality, and the lower temperature treatments were associated with very low mortality. Survival was 98 to 100% for craylings held at temperatures between 18°C and 22°C, and between 0% and 6% for craylings at temperature treatments of 25°C to 32°C. Mortalities within treatments between 25°C and 30°C, primarily occurred from day six to day eleven, corresponding with the initiation of moulting. Change of mass of crayfish was significantly higher with increasing temperature between 18°C and 22°C and at individual weights that suggest they had completed a moult. This study suggests a water temperature of 22°C is optimal for survival and growth in a nursery phase.