epiglucan and Flavobacteriaceae-Infections

β-glucan is one of the most potent immunostimulants enhancing innate immune activity, disease resistance and growth performance of many aquatic organisms. Nevertheless, there are few studies on feeding regimens of β-glucan that correlate to immune response and disease resistance and are important considerations for practical β-glucan utilization. Thus, the effect of β-glucan and feeding duration on innate immunity and disease resistance was investigated to establish an optimal feeding regimen of β-glucan for Nile tilapia (Oreochromis niloticus Linn.). A variety of β-glucan feeding regimens were evaluated, including: i) feeding for 2 weeks, ii) feeding for 4 weeks, and iii) feeding every-other-week, with the objective of establishing the optimal feeding regimen that enhanced innate immunity and disease resistance. Innate immunity parameters were determined every week for eight weeks. Alternative complement activity of all β-glucan groups was significantly (P < 0.05) increased at the end of the first week, and then fluctuated but was not significantly (P > 0.05) different to the control until the end of the trial. Increased lysozyme activity was only detected at the end of the second week in all β-glucan-treated groups, and then decreased to the control level during most of the sampling periods. Phagocytosis percentage was increased and prolonged by β-glucan feeding, while the phagocytic index was not. Apart from innate immunity, β-glucan-fed fish demonstrated enhanced disease resistance against Aeromonas hydrophila and Flavobacterium columnare challenge at only the end of the fourth week of the trial. The growth performance of β-glucan-fed fish was not significantly (P > 0.05) different among the experimental groups and control. Taken together, the result indicated that all β-glucan-feeding regimens resulted in quite similar outcomes with respect to innate immunity stimulation, disease resistance and growth performance. This novel result suggests that an every-other-week regimen is the optimal choice for Nile tilapia cultivation as an economic cost saving benefit. This is the first study to determine the optimal feeding-regimen of β-glucan to enhance innate immunity and increase resistance to infection by pathogenic bacteria in Nile tilapia.

Topics: Aeromonas hydrophila; Animal Feed; Animals; Aquaculture; beta-Glucans; Cichlids; Diet; Disease Resistance; Fish Diseases; Flavobacteriaceae Infections; Flavobacterium; Gram-Negative Bacterial Infections; Immunity, Innate

Bacterium Flavobacterium columnare is the causative agent of columnaris disease in many wild and farmed fish species. Immunostimulants are used with success in aquaculture against many pathogens, but the ability to improve innate resistance to columnaris disease has not been studied. Fingerling rainbow trout were treated with two immunostimulants, yeast beta-glucan and beta-hydroxy-beta-methylbutyrate (HMB). Selected innate immune function parameters, the production of reactive oxygen species (ROS) by whole blood and by isolated head kidney leukocytes, plasma lysozyme activity and complement bacteriolytic activity, were determined to assess the immune status of fish. The fish were then bath challenged with virulent F. columnare bacteria, and the mortality of fish was recorded. Given orally both stimulants raised the levels of immune function parameters, but did not improve survival in challenge at any concentration of the stimulants used. Intra peritoneal injection of beta-glucan increased parameter values several fold, but no beneficial effect of injected glucan on survival was noted. As a control, antibiotic medication administered prior to and during the challenge infection prevented the mortality. Innate immune mechanisms, even when induced to high levels with immunostimulants, as evidenced here, were not able to increase resistance against F. columnare. This may be connected to the external character of the infection. The results from the treatments with beta-glucan and HMB suggest that there is little prospect of preventing columnaris disease by means of immunostimulants in early life stage of rainbow trout. However, the efficacy of other immune stimulants remains open.

Topics: Adjuvants, Immunologic; Animals; Aquaculture; beta-Glucans; Complement System Proteins; Fish Diseases; Flavobacteriaceae Infections; Flavobacterium; Kaplan-Meier Estimate; Muramidase; Oncorhynchus mykiss; Reactive Oxygen Species; Valerates