Chinese herbs (Astragalus membranaceus and Lonicera japonica) and boron enhance the non-specific immune response of Nile tilapia (Oreochromis niloticus) and resistance against Aeromonas hydrophila

The effect of two Chinese medicinal herbs (Astragalus membranaceus and Lonicera japonica) and boron on non-specific immune response of Nile tilapia (Oreochromis niloticus) was investigated. Five diet variations in addition to a control diet (without herbs or boron) were used. These contained 0, 1 % Astragalus (with and without 0,05% boron), 0, 1 % Lonicera (with or without 0,05% boron) and a mixture of the two herbs with 0,05% boron. The diets were fed for four weeks, and respiratory burst and phagocytic activities of blood leukocytes; plasma lysozyme, total protein and total immunoglobulin level were measured weekly. After four weeks of feeding, fish were infected with Aeromonas hydrophila and mortalities were recorded. Results of this study showed that feeding tilapia with two herbs alone or in combination significantly enhanced phagocytic and respiratory burst activity of blood phagocytic cells. They had a moderate effect on the plasma lysozyme level and no effect on plasma total protein and total immunoglobulin level. Both herbs reduced the mortality following A. hydrophila infection. The lowest mortality was observed in the group fed with the combination of both herbs and boron. Combination of the herbs and boron could even more increase the survival rate of infected fish. It can be concluded that Astragalus and Lonicera extracts and boron supplementation added to fish feed can act as immunostimulants and enhance the immune response and disease resistance of cultured fish. (c) 2007 Elsevier B.V. All rights reserved.