Abstract

As the mortality of newly hatched 1-cm-long crayfish juveniles has been found to be very high in natural waters, methods for hatchery production of stage 2 juveniles and further rearing methods have been investigated. Fertile females were stocked in 100 m² ponds together with males in 1979, and 95% of surviving females were egg-bearing in the summer of 1980. Production of newly hatched stage 2 juveniles was found to be about 68 individuals per egg-bearing female. In 15 m² earthen ponds the juveniles feed only on natural food. With initial density 100 ind./m² the survival rate at the end of a 3-month growing period was 67%, while at an initial density 300 ind./m² it was only 32%. The mean size and weight at the end of the growing period were 21.4 mm and 221 mg at the lower density, which means an increase in biomass of 11.1 g/m². At the higher density, the mean size was 19.5 mm and weight 166 mg, or there was a biomass increase of only 4.7 g/m². In 4 m² plastic basins the juveniles were fed zooplankton and a mixture of fish, vegetables, and shrimp shell waste. The survival rate at an initial density of 100 ind./m² was 58% and at 300 ind./m² 50%. The mean weight at end of growing period in basins was only half that of pond-reared juveniles and the increase in biomass only 2.0 and 1.3 g/m² for respective densities.

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