60 March 2012 Table 3. Juvenile production of redclaw, Cherax quadricarinatus, hatched in tanks from 8, 12, 16, 20 or 24 females and nursed for a 30-day period. Parameters Females 8 12 16 20 24 Total weight of females (g) 512.75 686.75 940.75 1136.25 1347 Average weight of females (g) 64.09 57.23 58.80 56.81 56.13 Total juveniles hatched 3794 5082 6962 8408 9968 Biomass of females (g/m2) 178.04 238.45 326.65 394.53 467.71 Total Juvenile Production 1445a 1846a,b 2269b 2596b 1420a,b Juveniles/female 181a 154a 142a 130a 59b Juveniles/g/female 2.86a 2.69a 2.41a 2.27a 1.07b Biomass (g/m2) 192.71a 293.40a,b 305.56b 320.75b 233.51a Average weight of juveniles (g) 0.382a 0.454a 0.403a 0.381a 0.516a Survival % 38.1a 36.3a 32.6a 30.9a 14.2b 1Means within the same row with different superscripts are significantly different (P<0.05). juveniles is similar to the one obtained by Jones (1995a) who also nursed the juveniles for a 30-day period and reported an average weight of 0.4 ± 0.2 g/juvenile. Masser and Rouse (1997) projected juvenile sizes of approximately one gram but did not specify the nursery period length. Again, depending on the size required for stocking, nursery period can be lengthened or shortened, keeping in mind that it would affect survival. Hatchery managers generally tend to prefer producing large numbers at the expense of juvenile size, thus preferring short nursing periods. Experiment 3: Effect of nursery period and broodstock density on juvenile performance. An analysis of numbers of juveniles produced and average individual weight should be performed when deciding on the hatchery-nursery procedure to be used in commercial settings. Results of Experiment 3 suggest that a 30-day nursery period would maximize juvenile production without sacrificing average weight of individuals, and would also increase the amount of times a nursery tank could be used throughout the year, thus reducing capital costs. Appropriate nursery periods for Cherax quadricarinatus have not been determined and the 30-day nursery period used in Experiments 1 and 2, although arbitrary, was selected because Jones (1995a) used a 23 to 50 day period for his experiments. In the present experiment, juveniles maintained in the nursery for 30 days performed better than juveniles maintained in the nursery for 20 days or 40 days for all parameters studied except for average weight per juvenile, which was significantly less in the 20-day nursery period treatment than in the other two treatments (Table 4). Based on two-way ANOVA analysis, both nursery period and number of stocked broodstock significantly affected production. (Table 5). Juveniles held for 30 days in the nursery resulted in better total production, survival and biomass than juveniles held for 20- and 40- day nursery periods. Biomass (98.96 and 305.56 g/m2) in the treatvious studies (Jones 1995a, Masser and Rouse 1997). Furthermore, a trend suggesting a negative correlation between female number and juvenile survival was observed. In commercial operations, a decrease in survival would be acceptable only if the total production of juveniles is increased. Our results suggest that this is possible at stocking densities of 7 females/m2. Juveniles/female (59 to 181) and juveniles/g of female (1.07 and 2.86) in the treatment stocked with 24 females/tank were significantly less than in all other treatments. Total juvenile production in the treatment with 8 females/tank was significantly less than production in treatments stocked with 16 or 20 females/tank but similar to production in other treatments (Table 3). Total production of juveniles in Experiment 2 was 493901 juveniles/m2 and was superior to the total production of juveniles (135 to 202 juveniles/m2) projected by Masser and Rouse (1997) and comparable to the total production of juveniles (80-1212 juveniles/m2) reported by Jones (1995a). Although in Experiment 2, only the treatment stocked with 8 females/tank was different from all other treatments, a clear trend can be observed: Total juvenile production constantly increases as density of female increases from 3 females/m2 to 7 females/m2 and decreases at a density of 8 females/m2. Poor survival of juvenile at broodstock densities of 8 females/m2 could be because of the cannibalistic behavior of the juvenile redclaw. Cannibalism occurs mainly at the beginning of the nursery period when juveniles are competing for shelter areas. In the system we used, ample shelter was supplied and consequently cannibalism was not observed until juveniles reached a high density. Juvenile biomass produced in treatments stocked with 8 females/tank and 24 females/tank were significantly less than biomass in treatments stocked with 16 and 20 females/tank. Individual weight of juveniles at harvest (0.38-0.52 g) was not significantly different among treatments. Average weight of
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