Blood Lymphocyte and Neutrophil Response of Cultured Rainbow Trout, Oncorhynchus mykiss, Administered Varying Dosages of an Oral Immunomodulator – ‘Fin-ImmuneTM’

In a 10-week (May – August, 2008) Phase I trial, 840, 1+ rainbow trout, Oncorhynchus mykiss, received a commercial oral immunomodulator, Fin ImmuneTM, at four different dosages (0, 10, 20 and 30 mg g-1) to evaluate immune response and growth. The overall objective of was to determine an optimal dosage of this product for rainbow trout that provides enhanced immunity with maximal growth and health. Biweekly blood samples were taken from 10 randomly selected fish in each tank (30 samples per treatment) to evaluate the duration of enhanced immunity conferred by Fin-ImmuneTM. The immunological assessment included serum white blood cell (lymphocyte, neutrophil) densities and blood hematocrit (packed cell volume %). Of these three variables, only lymphocyte density increased significantly among trout fed FinImmuneTM at 20 and 30 mg g-1 which peaked at week 6. At week 7, all trout were switched to regular feed (lacking Fin-ImmuneTM) and by week 10, lymphocyte levels decreased among all levels but were still greater than at week 0. There was growth impairment at the highest dose of Fin-ImmuneTM tested (30 mg g-1) which can be associated with a physiological compensatory mechanism due to a dose-specific threshold level. Thus, our main objective of this Phase I study was achieved, the 20 mg g-1 dose of Fin-ImmuneTM should be the most efficacious (of those we tested) to use for a Phase II disease challenge trial. Keywords—Blood Lymphocyte, Neutrophil Response of Cultured Rainbow Trout, Oncorhynchus mykiss, Oral Immunomodulator – ‘Fin-ImmuneTM.