THE IMMUNOREGULATIVE EFFECTS OF LIQUORICE EXTRACT ON CRUCIAN

The problem of fish disease in both natural fisheries and in intensive cultivation systems is a major subject of scientific investigation1 Researchers try to solve this problem by all kinds of methods1 It is reported that many herbal medicines have very good characters to enhance the disease resistance of mammals1 However, these medicines are seldom used in aquaculture up to the present1 The aimof this study is to investigate whether there have immunoregulative effects of liquorice (Glycyrrhiza uralensis Fiseh)-one kind of traditional Chinese medicine on crucian(Carassius auratus) 1 In this study, liquorice was roughly extracted and then the extract was added in basal fish feed at the doses of 015% and 2% to raise crucian,which were subsequently sampled at day 14, 28, 35, 42 and 56 to examine their immune indexes, including serum lysozyme activity, serum bactericidal activity, lymphocyte count, phagocytic percent of leucocytes and spleen weight index, which are very typical immunological parameters referring not only to cellular immunity but also to humoral immunity1. The results exhibited that the serum lysozyme activity of low dose group increased gradually, and that of high dose group reached the maximum (205.5 ?28.8) U/ mL at day 35, then decreased slightly1 Serum bactericidal activityof both low and high dose groupsfluctuatedfrom 6210% to 7311% andfrom 75.0% to 83.3%, respectively1 At every sampling, serum bactericidal activity of control group, low dose group and high dose group rised in turn1 As to lymphocyte count, high dose group showed a higher value than control group only at day 42(p < 0105), but no statistical difference was found at other times1 Additionally, phagocytic percent of leucocytes of low dose group enhanced remarkably(p < 0105), and the maximum(6615 ?914)% ap2 peared at day 42, while that of high dose group increased, then decreased, with the peak value being(7417 ?516)% at day 351 Finally, spleen weight indexof low dose group was higher than that of control group at day 56(p < 0105), with the value being (1.08 ?0.09) × 10-3and(0.71 ?0.09) ×10-3,respectively1 Spleen weight index of high dose group was(1.12 ?0.13) × 10-3at day 28, higher than that of the control(0163 ?0108) ×10-31. As is known, teleost fish possess a variety of specific and nonspecific defence mechanisms against invading organisms1 When a pathogen penetrates the physical barriers of the animal, the first lines of defence it encounters are those of the nonspecific immune system1 Chemical defences attack the pathogen or mayopsonise it for further destruction by the cellular components of the nonspecific immune system1 Therefore, the nonspecific immune systemof fish is very important in resistance to disease1 The present study indicated that this kind of liquorice extract significantly improved some nonspecific immune indexes of crucian, such as lysozyme activity, bactericidal activity and phagocytic activity, showing its immunomodulatory effects on crucian and a promising future to apply in aquaculture1