Occurrence of Heterotrophic Bacteria in the Hemolymph of Japanese Coastal Crustacea

Abstract

The heterotrophic bacteria in the hemolymph of 13 species of Japanese coastal Crustacea were investigated. As a result, it was found that all the animal species examined possessed the heterotrophic bacteria in their hemolymph. Incidence of bacteria was low (20-29 %) in the hemolymph of Japanese spiny lobster, Panulirus japonicus and Kona crab, Ranina ranina but high (89-100 %) in other coastal Crustacea including crabs and hermit crabs. The mean bacterial densities in the hemolymph of coastal Crustacea ranged from 8.0×10⁰ to 1.1×10⁴ CFU/ml. There was no remarkable differences in both the incidence and bacterial densities either between male and female or between injured and normal individuals. Fifty specimens of a crab, Pachygrapsus crassipes were collected monthly during August to November, and bacterial populations of the hemolymph were analyzed. The Vibrio alginolyticus-like bacterium was dominant in August and September, while other Vibrio-like organisms and Gram-positive cocci predominated in October and November, respectively. These results strongly suggested that the microflora of the hemolymph of coastal Crustacea is easily influenced by environmental factors such as water temperature.