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 o f the freshwater crab Potamonautes warreni was investigated by comparison o f infested and uninfested crab populations from, respectively, a polluted a nd an unpolluted site along the Mooi River, North West Province, South Afri ca. Heavy gill infestations by bacteria (70%), peritrichous ciliates such a s Lagenophrys sp, (15%), Zoothamnium sp. (10%), and Epistylis sp. (5%), and motile protozoans resulted in species-specific lesions in the gill epithel ia of P. warreni and physiological changes in crabs from the polluted site. Bacterial colonies enmeshed in polysaccharide-like films produced indentat ions of the gill cuticular surfaces and dissociation of microvillous membra nes at the basal zone of epithelial cells of gill lamellae of P. warreni. L agenophrys sp. induced large subcuticular spaces with an unfolding or resor ption of the plasma membrane in the gill epithelia, The attachment of stalk s of Zoothamnium and Epistylis resulted in dilation of lamellar tissues, th e formation of vacuoles, and an increase in subcuticular spaces in the epit helia. Physiological changes in infested crabs included significant differe nces (P = 0.001) in increments of wet body mass and a reduced growth rate o ver time compared with uninfested crabs. The specific oxygen consumption (M -O2) in rested infested crabs significantly increased (31.29 +/- 5.8 mu mol O-2/kg/ min) compared with the M-O2 in uninfested crabs (27.92 +/- 5.6 mu mol O-2/kg/min; P = 0.009). The heart rate of infested rested P. warreni wa s significantly lower (40.77 +/- 13.79 beats/min; P < 0.02) than that in un infested crabs (61.09 <plus/minus> 29.02 beats/min) but the heart rate of i nfested crabs increased significantly with body mass (r = 0.53, P = 0.02). These findings suggest an interrelationship among organic pollution, microb ial gill infestations, and specific pathological and physiological response s in the crab host. The role of P. warreni and its microbial gill communiti es as bioindicators of pollution are discussed. (C) 2001 Academic Press.