We evaluated the effect of dietary supplementation with
mannan oligosaccharide (MOS) on the resistance to Aeromonas hydrophi1a
infection in Allogynogenetic crucian carp. The fish were randomly divided into five groups: a control group was fed with basal diet, and four treatment groups fed with basal diet supplemented with 60, 120, 240, 480 mg/kg MOS for 10 weeks, respectively. We then challenged the fish with A. hydrophi1a and recorded the mortality and the changes in serum
cortisol, T3, T4,
lysozyme,
alkaline phosphatase (ALP),
globin and hepatic total anti-oxidative capacity,
superoxide dismutase (SOD),
malondialdehyde (MDA) and the relative expression of
heat shock protein 70 (HSP70)
mRNA for a period of 7 d. Supplementation with 240 mg/kg MOS significantly increased serum ALP activity before
infection, 1d and 2d after
infection, serum
globin concentration prior to
infection, 1d and 7d after
infection, serum
lysozyme activity at 2d after
infection, T3 concentration at 2d after
infection, hepatic total anti-oxidative capacity prior to
infection, hepatic SOD activity at 7d after
infection and reduced serum
cortisol concentration at 2d after
infection, hepatic
malondialdehyde content at 1d and 2d after
infection. Supplementation with 480 mg/kg MOS significantly increased serum ALP activity before
infection, 1d and 2d after
infection, T3 content 1d after
infection, T4 content prior
infection and 7d after
infection, serum
globin concentration prior to
infection, 1d and 7d after
infection, serum
lysozyme activity prior
infection and 1d after
infection, serum total anti-oxidative capacity prior to
infection and 7d after
infection, hepatic SOD activity at 7d after
infection and the relative level of hepatic HSP70
mRNA at 2d and 7d after
infection, had decreased levels of serum
cortisol concentration before the
infection, at 2d after
infection, T4 concentration at 1d and 2d after
infection, hepatic
malondialdehyde content at 1d and 2d after
infection. Mortality was significantly lower in the group of 240 and 480 mg/kg MOS than the control. Our results suggest that ingestion of a basal diet supplemented with 240-480 mg/kg MOS can enhance resistance against pathogenic
infections in Allogynogenetic crucian carp.