Effect of endotoxin on the immunity of Indian major carp, Labeo rohita

Endotoxin, a lipopolysaccharide component of outer cell wall membrane of the Gram-negative bacteria is a factor responsible for a number of biological effects including immunostimulatory activities in different animal species including fish. In this study, L. rohita yearlings of weight ranging from 80 to 100 g were injected intraperitoneally with 0.5, 1, 2, 5, 10 and 20 EU/fish dose of endotoxin to find out its effect on the immunity. The L. rohita yearlings were found to resist the endotoxin dose up to 20 EU/fish and at the lower doses, i.e., at 1 and 2 EU/fish; it acted as an immune potentiator. Different serum and immune parameters like protein, globulin, lysozyme, respiratory burst activity, myeloperoxidase activity, natural agglutination titre were found to be significantly high (p < 0.01) at a dose of 1 EU/fish. While at 10 and 20 EU/fish, most of these parameters were lower thereby indicating the immuno-suppressive nature of the endotoxin at these higher doses.