Administration of a commercial immunostimulant preparation, EcoActiva™ as a feed supplement enhances macrophage respiratory burst and the growth rate of snapper (Pagrus auratus, Sparidae (Bloch and Schneider)) in winter

This study investigated the effects of prolonged administration of a commercial β-glucan based immunostimulant preparation, EcoActiva™, in the form of a feed supplement, on non-specific immune parameters and the growth rate of snapper (Pagrus auratus). Fish held at a temperature representing either summer or winter conditions, were sampled periodically and assayed for head kidney macrophage activity via in vitro superoxide production, and classical and alternative complement activity. Fish were also weighed monthly and the growth rate determined. Fish fed on a diet supplemented with EcoActiva™ and held at the winter temperature had a significant enhancement of macrophage superoxide anion production upon stimulation with phorbol myristate acetate (PMA), and this increased activity was maintained throughout the trial. Macrophage activity in fish fed the supplemented diet and held at the summer temperature was also increased. However, EcoActiva™ failed to increase either classical or alternate complement activity. Most significantly EcoActiva™ resulted in an increase in growth rates of the fish held at the winter temperature as compared to the control fish, although no difference was seen between the groups held at the summer temperature. These results suggest that routine incorporation of β-glucan preparations like EcoActiva™during winter may enhance macrophage function and growth rates at a time of increased disease susceptibility and little or no growth.