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This experiment was conducted to investigate the effects of fucoidan on the blood constituents,anti-oxidation and innate immunity of juvenile yellow catfish, Pelteobagrus fulvidraco.Totally 420individuals of juvenile yellow catfish were randomly allocated to 7 groups with 3 replicates per goup and20 fishes per replicate.The same experimental fish were randomly subjected to one of the following 7treatments for 12 weeks: The basal diet was applied as control group, the experimental groups were fed on fucoidan extracted from Sargassum horneri (SF) and commodity fucoidan purchased from the market (MF),and the effective dosages were 0.05%, 0.1% and 0.2% per kilogram feed (the groups were respectively marked as SF1, SF2, SF3, MF1, MF2 and MF3).The capabilities of anti-oxidation and innate immunity were detected by the blood characters, serum enzyme activity, serum MDA content, respiratory burst activity and phagocytic index of head-kidney macrophages.Challenge test was conducted also.The results indicated that the triglyceride (TG) and total cholesterol (TC) values of the yellow catfish were significantly decreased when dietary with SF and MF, while there was no significant difference between the MF1 and the control group.Fish fed on SF and MF diet had a lower high density lipoprotein (HDL) level than those fed on basal diet except SF2 group.Thelow density lipoprotein (LDL) and glucose(GUL) levels of the fish were significantly decreased at the 0.2% dietary fucoidan level, and there were no significant difference between the other groups.The activities of serum superoxide dismutase (SOD) were significantly increased and the contents of malondialdehyde (MDA) were significantly decreased when the fish fed dietary with SF and MF.The CAT activities of SF groups were higher than the control groups, while the values were not significantly changed in MF1 and MF3 groups.The maximum of catalase (CAT) activities were obtained in the SF2 and MF2 groups (fucoidan=0.1%).The serum lysozyme (LZM) activities of the yellow catfish fed on SF and MF were significantly higher than the control ones except SF3 group.Phagocytosis index (PI) and the respiratory burst (RB) activity of head-kidney were significantly influenced by dietary fucoidan, PI values of the fish fed on SF2, MF1 and MF2 were higher than those fed on basal diet.RB activity of the yellow catfishes were significantly increased when they were fed on fucoidan except the SF3 and MF3 groups.The challenge experiment with Aeromonas hydrophilalala revealed that the fish fed on fucoidan had no significant effect on mortality rate of the yellow catfish.These results suggested that fucoidan significantly influences the blood characters, antioxidant status, non-specific immune responses in juvenile yellow catfish.