The effect of inter- and intra-specific competition on survival and growth rate of native juvenile noble crayfish Astacus astacus and alien spiny-cheek crayfish Orconectes limosus

Juvenile noble crayfish, Astacus astacus and spiny-cheek crayfish, Orconectes limosus were reared from the 2nd and the 3rd developmental stage (i.e. since the stage of independence), respectively, until the end of the growing season. The first period revealed very low survival rate of O. limosus in the communal stock (7 +/- 6.2%), probably caused by predation of A. astacus. Separately reared O. limosus proved significantly higher survival rate (49 +/- 9.2%) than those in the communal stock with A. astacus. The latter species also showed the highest survival rate in this case (90 +/- 7.1%). This was not found to differ from the survival rate of separately reared noble crayfish (86 +/- 3.1%). In general, both the significant effect of bigger size of A. astacus than that of O. limosus and higher intra-specific cannibalism of O. limosus were reflected during the first phase of rearing. Size and weight of both species were equivalent 11 weeks after hatching (8 weeks of rearing). The higher cumulative survival rate was reached in the intraspecific culture of A. astacus (90%) while low cumulative survival of both species was found in communal stock (less than 50%) in the second phase of rearing. At the end of the growing season, 19-week-old O. limosus attained a higher mean size and weight but were more variable in the group (29.3 +/- 5.17 mm and 616.4 +/- 412.53 mg) than A. astacus (21.2 +/- 1.82 mm and 229.9 +/- 59.45 mg). Single and communal stock did not differ. Growth of O. limosus was much faster than that of A. astacus.