Fish Diseases and Management

3.1.1.Non-specific defence mechanisms

Surface barriers

mucus: Whole integument of the fish is covered with mucus, which entraps microorganisms, and continuous secretion of the mucus inhibits colonisation of microorganisms on the integument.

Skin: Epidermal integrity is vital to fish for maintaining osmotic balance and excluding microorganisms. Epidermal healing is comparably faster in fish even at low temperature. Malpighian cells migrate from periphery of the wounds over the surface rapidly closing the lesion. Epidermis also responds to non-specific irritation by thickening of the cuticle.

Gills: Large surface area of delicate epithelium is available on gills, which has mucus protection. The gill is considered to be an important route of pathogen entry. This organ is highly responsive and results in hyperplasia in the event of any irritation. The gills also contain phagocytic cells, which seen in the branchial capillaries.

Gastrointestinal tract: The lining of the GI tract is similar to skin in many aspects. The digestive function of the gut provides an extremely hostile environment to invading pathogens by the low pH and due to the secretion of bile.