The use of immunostimulants to control Aeromonas hydrophila infections in rainbow trout, Oncorhynchus mykiss (Walbaum)

Objective: To examine the effects of immunostimulants in enhancing the immune defense mechanisms of rainbow trout against Aeromonas hydrophila borne infections; to determine the possible mode of action(s) of these immunostimulants; possibly to establish the most effective dose(s) against A. hydrophila infections; and to assess the dietary effect of immunostimulants on growth performance of rainbow trout. Method & Materials: A group of 125 rainbow trouts, average wt. 15g were fed basal diet supplemented with 0g, 0.1g, 0.5g and 1.0g of immunostimulants 100g of feed for 14 days. They were challenged i.p with Aeromonas hydrophila inoculum at the end of the feeding trial. Mortality and behavioral alterations were monitored daily for 14 days. Dead fish were examined for evidence of disease after Austin & Austin, 1999. The following parameters were also examined in both immunostimulants treated fish and the controls to ascertained their mechanism in immunemodulations: Haematological, serum/blood biochemical and immunological indices. Results & Conclusion: Immunostimulants, which was fed at 0g, 0.1g, 0.5g and 1.0g 100g-1 of feed for 14 days to rainbow trout (Oncorhynchus mykiss, Walbaum) led to the control against experimental infections by Aeromonas hydrophila. At doses 0.5g and 1.0g immunostimulants (denoted as EN 1 and EN 2) 100g of feed, there was a reduction in mortalities of 0 to 4% compared to controls (88%). Moreover, there was a significant increase in growth, feed conversion ratio and protein efficiency. There was stimulations of non-specific immune parameters involving the proliferation of immune cells, mostly the lymphocytes and neutrophils, enhancement of phagocytic activity, oxidative burst, lysozymes, anti-protease and bactericidal activity, following immunostimulants treatments. Immunostimulant used in this study, provides a new perspective for use as prophylactic agent and indeed, ‘green solution’ to prevention and control of bacterial pathogens in fish cultures. Immunostimulants EN1 and EN2 modulate the immunological mechanism of rainbow trout against A. hydrophila infections. Thus it can be concluded that they can be used to up-regulate the immune defense mechanism and disease resistance of most fish species in aquaculture.

کلیدواژه ها:

Immunostimulant ، Non-specific immune response ، Aeromonas hydrophila ، Haemorrhagic septicaemia ، rainbow trout