ABSTRACT
This chapter describes some mechanisms of immunological compromise that may be affected by environmental stressors. Fish appear to possess lymphocyte subpopulations and immunoglobulins analogous to other vertebrates and thus show immunological specificity and memory. Polymorphonuclear cells and macrophages of fish and macrophage-like blood cells of bivalves are thought to play important roles in internal defense systems, regardless of the relative sophistication of the host’s adaptive immune capabilities. Molluscan hemocytes are also known to play an important role in detoxification of pollutants, such as heavy metals. Interpretations of the effects of experimental manipulations as indicated by changed hemocyte counts in hemolymph samples must be made with caution. The biological role of serum lysozyme in bivalve molluscs is commonly thought to be involved with internal defense mechanisms by virtue of its antimicrobial activity.
