Interactive cellular and physiological responses of the freshwater crab Potamonautes warreni to cadmium and microbial gill infestations.

Cellular and physiological responses of the freshwater crab, Potamonautes warreni, to cadmium and microbial gill infestations were investigated. Infested crabs were collected from the Mooi River, at Noordbrug, Northwest Province, South Africa in the autumn of 1995 and exposed to 0.2mg Cd(2+)L(-1) or kept unexposed under constant laboratory conditions for 7, 14 and 21 days at 24 degrees C. Cellular lesions with microbial gill infestations were persistent over 21 days and showed a similar species diversity and density as recorded in the previous summer [Schuwerack et al., 2001a. Pathological and physiological changes in the South African freshwater crab, P. warreni Calman induced by microbial gill infestations. J. Invertebrate Pathol. 77(4), 259-269]. With Cd exposure the microbial community disappeared and crabs showed a higher mean but wider range in ammonia excretion and lower mean O:N ratio after 7 days. After 14 days exposure to Cd, time- and stressor-specific cellular and physiological responses included degeneration of oxygen and gas exchange gill tissues and a mean reduced growth rate, ion exchange, a significantly reduced O:N ratio (P<or=0.05) and induced hemolymph pH (P<or=0.05). Both stressors, i.e. gill infestation and Cd, produce a barrier, which obstructs pathways in ion exchange and oxygen uptake, resulting in NH(3)/NH(4)(+) retention and similar physiological responses after 21 days. The interactive cellular and physiological mechanisms in P. warreni exposed to multiple stress are discussed.