The humoral immune response of Salmo trutta L. and Cyprinus carpio L. exposed to heavy metals

Salmo trutta L. and Cyprinus carpio L. were exposed to low levels of waterborne heavy metals, 0.75 mg Ni dm^-3, 1.06mg Zn dm^-3, 0.29 mg Cu dm^-3 and 1.01 mg Cr dm^-3, at pH 7.83, water hardness 206.9 mg CaCO, dm^-3, and water temperature 15.5° C. During a 38 week exposure period, the humoral antibody response to MS2 bacteriophage was followed using a 50% viral neutralization assay (SD₅₀) method. A suppression of the immune response was observed in fish exposed to the four heavy metals. Total suppression of the humoral antibody response was found only in C. carpio exposed to Cu or Cr, and these fish exhibited symptoms of acute toxicosis. The time for the primary blood clearance of live bacteriophage was increased in S. trutta exposed to the heavy metals, with the exception of Zn-exposed fish, and in C. carpio exposed to Cu. Following the suppressed primary responses, the Ni-exposed S. trutta and Zn-exposed C. carpio exhibited an adjuvant-like response to the second bacteriophage challenge.