Defense mechanisms and disease prevention in farmed marine invertebrates

In addition to xenobiotic assaults, cultured bivalve mollusks (mussels and oysters) and crustacean arthropods (Penaeid shrimps) are continuously confronted with infectious microorganisms. The deadly effect of infections are most probably underestimated as the diseased animals rapidly vanish in nature, and only in aquacultural farms are mortalities reported as causing economical breakdowns. To fight severe epizootic infections and to stabilize production, we have to simultaneously extend our knowledge on their immune defense systems and develop multiple strategies for promoting disease resistance. The presence of macrophage-like phagocytes and several morphologically distinguishable circulating hemocyte types have been reported as well as some humoral activities. More recently, activities related to vertebrate innate immunity have also been described, including inflammatory processes and the generation of radical oxygen intermediates (ROIs) and nitric oxide (NO), cytotoxic proteins and several families of antimicrobial peptides. Concerning the strategies to increase disease resistance, immunodiagnostic techniques for early detection of the pathogens are under development using molecular probes and antibodies. As not all individuals within a species suffer from certain diseases, programs of genetic selection have been instituted. Finally, genetic engineering have been employed to characterize immune gene regulation mechanisms that might be used for transgenesis or as selection criteria. (C) 1999 Elsevier Science B.V. All rights reserved.