Article

Short- and long-term effects of a dietary yeast β-glucan (Macrogard) and alginic acid (Ergosan) preparation on immune response in sea bass (Dicentrarchus labrax)

ICRAM, Institute for the Research Applied to the Sea, Rome, Italy; Department of Environmental Sciences, Tuscia University, Viterbo, Italy; Department of Biology, University of Ferrara, Italy; Department of Comparative Biomedical Sciences, University of Teramo, Italy; Hendrix, Udine, Italy
Fish & Shellfish Immunology DOI:10.1016/j.fsi.2004.08.003

ABSTRACT The present study investigated the immunomodulatory activity of Ergosan, an algal extract containing alginic acid, and Macrogard, a yeast extract containing β-glucans, on innate and specific immunity in sea bass (Dicentrarchus labrax). Four cycles of experimental feeding using normal fish feed formulation (control group) supplemented with Ergosan (0.5%) or Macrogard (0.1%) were performed at 60-day intervals (15 days of treatment + 45 days of suspension). Serum complement, lysozyme, total proteins and heat shock protein (HSP) concentrations were measured at 15, 30 and 45 days from the end of the first 15-day feeding cycle (short term) and 45 days after the end of each feeding cycle over a 35-week period (long term). The percentage of B- and T-lymphocytes in peripheral blood leucocytes and gut were measured over long-term trial.Significant elevation (P < 0.05) in serum complement activity occurred in sea bass fed with alginic acid and glucans, at 15 days from the end of first cycle of treatment. Significant elevation (P < 0.05) in serum lysozyme, gill and liver HSP concentration were observed in the same experimental groups at 30 days from the end of treatment, whereas a significant increase (P < 0.05) of complement activity was only observed in fish that received an Ergosan diet. At 45 days from the end of treatment, complement, lysozyme and HSP concentration did not differ among groups.Over the long-term period, no significant differences were observed in innate and specific immune parameters, survival, growth performances and conversion index in treated and control fish. A dramatic decrease of both innate and acquired immune parameters was observed during the winter season in all groups, followed by a partial recovery when water temperature increased. Reduction in complement and lysozyme activities was significatively correlated (p < 0.01) to water temperature variation. The results suggested the potential of alginic acid and β-glucans to activate some innate immune responses in sea bass, and particularly under conditions of immunodepression related to environmental stress.

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Keywords

35-week period
 
60-day intervals
 
control fish
 
environmental stress
 
Ergosan diet
 
experimental groups
 
HSP concentration
 
innate immune responses
 
liver HSP concentration
 
long-term period
 
long-term trial.Significant elevation
 
partial recovery
 
sea bass
 
serum lysozyme
 
short term
 
Significant elevation
 
specific immunity
 
total proteins
 
water temperature
 
winter season