Redclaw, Cherax quadricarinatus sex-separated rearing strategy enhances reproduction in females

Redclaw crayfish Cherax quadricarinatus, a tropical freshwater species, native to Northern Australia and is regarded as a promising species for global expansion of aquaculture. However, poor female fertility is a hin-drance towards the commercial production of redclaw. The present study investigated if dissociated; pre -exposure of female redclaw to males can stimulate spawning and increase reproductive efficiency. The study was conducted in dissociated (111 days) and associated (34 days) phases. Redclaw were held in vertical recir-culating aquaculture systems with each system consisting of 42 individual compartments (45 cm length x 33 cm width x 25 cm height) arranged as six compartments horizontally and seven compartments vertically. The average body weight of females was 66 +/- 2.2 g. In the dissociated phase, females were either kept alone (0M, n = 36) or were exposed to either 1 (1M, n = 36) or 2 (2M, n = 36) males suspended in the uppermost row of the system. During the associated phase, females (n = 108) were maintained at a sex ratio of 1M:1F. During the dissociated phase, the spawning rate was less in the control compared to the male exposed groups (2.8%, 1/36, 18.1%, 13/72 respectively; p = 0.026). However, the moulting rate was greater in the control compared to the male exposed groups (22.2%, 8/36; 5.6%, 4/72 respectively; p = 0.009). During the associated phase, there were no significant differences in spawning rate (22.2%, 8/36 and 33.3%, 24/72), mean days to spawning (21.88 +/- 3.06 and 16.38 +/- 2.35), moulting rate (11.1%, 4/36 and 6.9%, 5/72) and mean days to moulting (24.50 +/- 3.97 and 22.40 +/- 3.93) in the control and male exposed groups, respectively (p > 0.05). However, the mean total number of eggs (670.9 +/- 26.0 and 507.0 +/- 29.36), fecundity (11.00 +/- 0.59 and 6.14 +/- 0.47), the hatching rate (89.70 +/- 1.31% and 77.50 +/- 9.24%) and the total number of juveniles produced (545.70 +/- 42.50 and 343.30 +/- 37.47) during the associated phase were greater in the male exposed groups compared to the control group respectively; p < 0.05). It was concluded that pre-exposure of redclaw females to males in a dissociated recir-culation system, increases spawning rate during a dissociated phase, and after exposure to males improves egg and juvenile production during an associated phase. Such a breeding strategy has potential to increase hatchery productivity.

Automated summary

This study investigated the effect of pre-exposure of female redclaw crayfish to males on spawning and reproductive efficiency. The results showed that during the dissociated phase, the group exposed to males had a higher spawning rate but a lower molting rate. During the associated phase, there were no significant differences in spawning rate and molting rate between the exposed and control groups, but the exposed group had higher egg and juvenile production.