Successful sex ratio of 1M:4F in the astacid crayfish Pacifastacus leniusculus Dana under captive breeding conditions

In astacid crayfish breeding, a sex ratio of one male to two females (1M:2F) is usually recommended. In light of the fact that an increase in the proportion of females in the broodstock would be desirable, two experiments were carried out with Pacifastacus leniusculus Dana to test a proportion of females with a ratio as high as 1M:4F under different conditions of animal density and group size, with mating and spawning rates being evaluated in addition to the production and further viability of the eggs. In both experiments, no breeder mortality was recorded and all the females mated. No significant differences were noticed between groups of 5 and 125 animals nor between densities of 5 and 25 animals per square metre. Likewise, no differences were detected between the sex ratios 1M:2F and 1M:4F. With regard to overall results, some 10 days after spawning 98% of egg-bearing females was achieved, with a mean of 323 pleopodal eggs. When the eggs reached phases VII-IX (embryo with blastopore in closing process-embryo with naupliar appendages), the percentage of berried females was 93.6% with 245 eggs per female. At that point, eggs were stripped, pooled and artificially incubated by methods developed by this team. Finally, 165 stage 2 juveniles were obtained per female. This allows, at least in this species, a considerable increase in the proportion of females in the broodstock, and better use of farming facilities.