Pathological and Physiological Changes in the South African Freshwater Crab Potamonautes warreni Calman Induced by Microbial Gill Infestations

The impact of microbial gill infestations on the pathology and physiology of the freshwater crab Potamonautes warreni was investigated by comparison of infested and uninfested crab populations from, respectively, a polluted and an unpolluted site along the Mooi River, North West Province, South Africa. Heavy gill infestations by bacteria (70%), peritrichous ciliates such as Lagenophrys sp. (15%), Zoothamnium sp. (10%), and Epistylis sp. (5%), and motile protozoans resulted in species-specific lesions in the gill epithelia of P. warreni and physiological changes in crabs from the polluted site. Bacterial colonies enmeshed in polysaccharide-like films produced indentations of the gill cuticular surfaces and dissociation of microvillous membranes at the basal zone of epithelial cells of gill lamellae of P. warreni. Lagenophrys sp. induced large subcuticular spaces with an unfolding or resorption of the plasma membrane in the gill epithelia. The attachment of stalks of Zoothamnium and Epistylis resulted in dilation of lamellar tissues, the formation of vacuoles, and an increase in subcuticular spaces in the epithelia. Physiological changes in infested crabs included significant differences (P = 0.001) in increments of wet body mass and a reduced growth rate over time compared with uninfested crabs. The specific oxygen consumption (ṀO2) in rested infested crabs significantly increased (31.29 ± 5.8 μmol O2/kg/min) compared with the ṀO2 in uninfested crabs (27.92 ± 5.6 μmol O2/kg/min; P = 0.009). The heart rate of infested rested P. warreni was significantly lower (40.77 ± 13.79 beats/min; P < 0.02) than that in uninfested crabs (61.09 ± 29.02 beats/min) but the heart rate of infested crabs increased significantly with body mass (r = 0.53, P = 0.02). These findings suggest an interrelationship among organic pollution, microbial gill infestations, and specific pathological and physiological responses in the crab host. The role of P. warreni and its microbial gill communities as bioindicators of pollution are discussed.