Fish Immunology (1+1)

Unit 3- Nonspecific immunity

3.2. Physical barriers
The epithelial and mucosal barrier of the skin, scales, gills and alimentary tract act as the first barrier to infection. This physical barrier is much important in fish because the fish being aquatic in nature and constantly immersed in water that contain potentially harmful agents. The mucus of fish contains lectins, pentraxins, lysozymes, complement proteins, antibacterial peptides and immunoglobulin M (IgM), which have an important role in inhibiting the entry of pathogens. In addition, the epidermis is able to react by thickening and cellular hyperplasia to different attacks and its integrity is essential for osmotic balance and to prevent the entry of foreign agents. On the other hand, defending cells such as lymphocytes, macrophages and eosinophilic granular cells are also present.