BENTHIC SUBSTRATE ENHANCES EARLY SURVIVAL OF AUSTRALIAN REDCLAW CRAYFISH Cherax quadricarinatus IN A RECIRCULATING NURSERY SYSTEM
Australian redclaw crayfish, also known as freshwater lobsters, are a new and promising aquaculture species. Fast growth rates, easy care and maintenance, combined with a high market value make this species attractive to the aquaculture industry. However, development of a domestic freshwater lobster industry is largely hampered by the need for a reliable supply of seed stock. This study examined two types of benthic substrates to determine whether production of 45-day old craylings could be enhanced.
Hatchling survival and growth were studied in an array of eight, 77 liter glass aquaria in a closed recirculation system. The bottom surface area of each tank was 2288 cm2 (30.5 cm x 75 cm). Average temperature was 26.2oC and day length was 14 hours.
In one set of experiments the bottom was covered by limestone rock, with particle sizes of 1-2mm, 4-8 mm, 16-32mm & 32-64 mm. Hatchlings were stocked at densities of 0.022, 0.044 and 0.066 cm2 (50, 100, 150 individuals). In the other set of experiments, black low density Matala filtration media was used in 6, 8, 10, 12 layers (930 cm2 each) on top of an 8-16 mm gravel substrate. Hatchlings were stocked at densities of 0.011, 0.022, 0.033, and 0.044 cm2 (25, 50, 75, 100 individuals).
Survival was highly variable ranging from 4-88% in the Matala and 2-58% in the rock. However, Matala (46.4%) had double the survival rate than stone (22.3%), when the same stocking densities were compared (chi square test, P <05). In 12 experimental trials, survival on a stone substrate was greater than 50% only 8% of the time, while survival on Matala was greater than 50% in 63% of the trials.
Growth was also highly variable with final average weights ranging from 0.20 - 1.06 g in Matala and 0.57 - 2.02 g in the rock. Weight of craylings after 45 days was significantly better with the rocky substrate than the Matala (T-test, P < .01).
Biomass production was 2.7 times greater with 6 layers of Matala (5580 cm2) over that of the bare gravel substrate. However, adding additional layers of Matala did not increase production. Coarse gravel (32-64mm) had the highest production of the rock substrate.
In summary, the addition of substrate significantly increased survival and production of redclaw craylings. Matala performed better than the coarse rock, yielding a higher survival percentage and was easier to handle when capturing the craylings at the completion of trials.