Immune Response Of Channel Catfish, Ictalurus Punctatus Against Dietary Ysest Complex And Its Administration Process

Channel catfish, Ictalurus punctatus, inoculated with formalin killed Cytophaga columnaris were feed supplemented with appropriate amount of yeast complex. 28 days. In oeder to investigate the infulence of yeast complex on immune enhancement of immunized channel catfish, the gained weight, agglutinating antibody titer, lysozyme activity, serum glutamic pyruvic transaminase (SGPT) total protein in serum, phagoeytic activity and relative percent survival (RPS) after challenge with live C. columnaris of experimental channel catfish were monitored. The results showed that adding yeast complex with a ratio of 200.0 mg/kg·d^-1 into the feed of channel catfish can upgrade the immune response level, strengthen their resistance to C. columnaris as well as improve their liver function and prompt their growth to some degree.In order to study the effect of yeast complex on non-specific immune function of Ictalurus punctatus, the fish were fed with diets supplemented with different amount of yeast complex (diets supplemented were formulated to contain 0g/kg, 0.5g/kg, 2g/kg and 4g/kg yeast complex respectively), and the phagoeytic activity of leukocytes in blood, lysozyme activity in serum, the content of serum complement C₃ and C₄ in serum were tested on 0, 7th, 14th, 21st, 28th, 42nd and 56th day. The results showed that the phagoeytic activity of leukocytes in blood, lysozyme activity and the content complement C₃ and C₄ in serum in groups contained yeast complex were markedly enhanced, especially the addition of 2g/kg yeast complex in diet were significantly higher than the control group (p<0.05) and that were higher than the addition of 0.5g/kg and 4g/kg yeast complexs in diet. The mortality of 2g/kg yeast complex challenged with live Aeromonas hydrophila was lower than others.Channel catfish, Ictalurus punctatus were continuously fed with feed supplemented with yeast complex at the dose of 1000.0mg/kg. B. W. every 10 days, 10 fish from experimental and control group respectively were blooded, and the non-specific immune parameters including the phagocytic activity of the leucocytes, lysozyme activity, bactericidity and compliment activity in the serum were monitored in order to investigate the relationship between the continuous feeding period of dietary yeast complex and the efficacy of stimulation. The results showed that after 10 days of continuous feeding, the phagocytic activity of the leucocytes, lysozyme activity, bactericidity and compliment activity in the serum were significantly higher than that of the control group, and were on the continuous increase during the 40 days. The phagocytic activity of the leucocytes reached the highest level after 40 days of feeding, followed by a gradual decline, and showed no significant difference between the experimental and the control group (t-test, p>0.05) after 70 days of continuous feeding. The lysozyme activity and compliment activity reached the highest level after 50 days of feeding, followed by a decline, and showed no significant differences between the experimental and the control group (t-test, p>0.05) after 80 days of continuous feeding. From the above research results, it was suggested that the optimal period to feeding Channel catfish continuously with yeast complex is no more than 40 days.