Chapter 14 – Immune System

Publisher Summary This chapter focuses on the identification and discussion of grossly visible tissues and changes in organs responsible for immunity in fish. In teleost fish, the thymus is normally pale white. However, severe systemic infections that penetrate the thymus result in a red and hemorrhagic surface. The thymus produces T-cell lymphocytes that appear to be involved in allograph rejection, enhanced macrophage function, and antibody producing B-cell stimulation. Commonly, this organ becomes more flattened or involuted with age or in response to long periods of stress. Chronic infections of the kidney and spleen with Mycobacteria spp. produce characteristic white or pale yellow granulomatous lesions particularly common in aquarium fish species. The immune functions of the kidney include phagocytosis, antigen processing, IgM-like antibody formation and immunologic memory. Antigen from an intraperitoneally injected vaccine is transported, processed, and localized in areas adjacent to melanomacrophage aggregates in kidney, spleen, and liver.