Vibriosis Due to<i>Vibrio mimicus</i>in Australian Freshwater Crayfish

Abstract

The pathogenicity of Vibrio mimicus for two commercially cultured species of Australian freshwater crayfish, the yabbie Cherax albidus and the red claw Cherax quadricarinatus was investigated. Total aerobic mesophilic bacterial counts were obtained from hemolymph extracted from live crayfish. Bacteria were found in the hemolymph of 100% of C. albidus and 98% of C. quadricarinatus sampled; 45% and 54% of each species, respectively, had concentrations of more than 100 colony-forming units/mL. Aeromonas, Acinetobacter, Vibrio, Micrococcus, and Staphylococcus were the predominant bacterial genera isolated from both species of crayfish. Vibrio mimicus was isolated from 14% of the C. albidus sampled over 3 months. Three of seven V. mimicus isolates were virulent and produced rapid mortalities when 105 viable cells were inoculated into crayfish by intramuscular injection. Inoculation with lysed cells and filtered culture supernatants produced no mortalities. Ribotyping was used to study relationships among the V. mimicus isolates. Eleven ribotypes were observed among 18 isolates with different pathogenicity for crayfish. We confirmed that strains of V. mimicus present in the aquaculture environment can produce systemic disease in two commercially cultured species of crayfish.