World Aquaculture 59 negative effect on Survival or Average weight of juvenile redclaws. Experiment 1: Effect of water volume on juvenile production Results of the present experiment are presented in Table 2. No significant differences among treatments were observed in total juvenile production (1147-1516), juveniles/ female (68-168), juveniles/g of female (1.11-2.12), biomass (235-322g/m2), average weight of juveniles (0.55-0.65g) or survival (15-29 percent) although the ranges of reported results were large. However, there was an apparent trend where survival decreased as stocking density increased. D’Abramo (2000) reported that weight gain for Macrobrachium rosenbergii was maximized through a simultaneous increase in water volume and surface area. However, their experiment did not assess the effect of increased water volume alone. Our results suggest that increasing volume beyond a certain minimum is without effect but female stocking density has a significant effect on juvenile weight. Therefore, if the goal is to increase average individual juvenile weight, irrespective of total production, we should reduce stocking density of brood females. If number of juveniles produced is important, manipulating brood stocking density is not effective. Experiment 2: Effect of female stocking density on juvenile growth and survival Stocking between 12 and 20 (4.1 to 6.9/m2) females/tank had no effect on average weight of juveniles produced, yet resulted in best Total Juvenile Production. Accordingly, if Table 2. Juvenile production of redclaw, Cherax quadricarinatus, hatched in tanks and nursed for a 30-day period. Parameters 9FV1 9FV2 18FV2 P. Value PSE2 Area (m2) 2.84 2.84 2.84 Depth (cm) 10 10 20 Females 9 9 18 Females/m2 3.17 3.17 6.35 Total weight of females (g) 721 591 1101 Average weight of females (g) 80.19 65.74 61.2 Estimated juvenile/ gram of female 7.4 7.4 7.4 Total juveniles hatched 5340 4378 8152 Nursery period (days) 30 30 30 Total juvenile production 1516 1147 1225 0.528 230.709 Juveniles per female 168.48 127.48 68.07 0.082 25.518 Juveniles/g/female 2.12 1.95 1.11 0.174 0.350 Biomass (g) 322 235 235 0.218 35.596 Average weight of juveniles (g) 0.65 0.59 0.55 0.744 0.098 Survival % 29 26 15 0.174 4.731 1No significant differences were found between treatments (P>0.05). 2Pooled standard error of treatment means (n=3). hatcheries can make more profit by selling large numbers of small juveniles than by selling smaller quantities of larger juveniles, a female broodstock density of 4 to 7/m2 is advised. Handling of newly hatched redclaw juveniles usually results in very poor survivals. Accordingly, a hatchery/nursery technique where a number of berried females are placed in hatchery tanks, their eggs allowed to hatch, and females removed when broods drop off seems to produce healthier and more numerous juveniles (Jones 1995a, Masser and Rouse 1997, Parnes and Sagi 2002). This hatchery-nursery protocol has been preferred by redclaw producers in Australia and Latin America. A drawback to such a system is lack of good production estimates but this can be mitigated by weighing the females and then estimating 7.8 eggs/g female and a 90 to 95 percent survival of hatchlings as suggested by Yeh and Rouse (1994) and observed in the first part of the present work. However, it is recommended that hatchery operators calculate survival specific to their operation to increase the accuracy of their estimates. Masser and Rouse (1997) recommended that stocking density of juveniles in nursery tanks should not exceed 270 juveniles/m2 whereas Jones (1995a) stocked juveniles at densities between 980 and 1842 /m2. In the present work, juveniles were stocked at 1317-3461/m2, significantly more than recommended by other workers. This increase in stocking densities might be the reason for poor survivals (14.2 to 38.1 percent) observed in Experiment 2. Survival in the treatment stocked with 24 females/tank was significantly less than survival in all other treatments (Table 3), and survivals in all treatments were inferior to survivals reported in pre-
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