The Efficacy of Oral Immunostimulants in Enhancing Resistance against Microsporidiosis in Juvenile Atlantic Cod (Gadus morhua L.)

摘要

The intracellular parasite Loma morhua (Microsporidia) can induce severe pathology in juvenile Atlantic cod (Gadus morhua L.), characterized by the formation of conspicuous white xenomas in the gills, heart, and spleen. In the absence of suitable chemotherapeutants and given the potential problem of microsporidiosis to a commercial cod aquaculture industry, studies are ongoing to determine the efficacy of various commercial immunostimulant products as prophylactic treatments. In the present study, juvenile, hatchery-reared cod were fed a formulated gadoid diet treated with one of four immunostimulant products, while control groups received untreated feed. Immunostimulant formulations were based on one of three product classes: beta-glucans, bioflavinoid, or nucleotide supplements. To evaluate product efficacy, growth rates were monitored, and random, peripheral blood samples were analyzed for lymphocyte density as an indicator of immune system activity. Finally, the cod were exposed to the infective spores of L. morhua, and the trials were terminated either two (Trial 1) or six weeks (Trial 2) post-challenge. Increased terminal lymphocyte densities were found in all beta-glucan groups for both trials and decreased prev -alence of heavy to severe infections with L. morhua for both beta-glucan and nucleotide supplement groups in Trial 2.