| Summary: | The present investigation was carried out to study the inflammatory response of carp (Cyprinus carpio L. ) to various stimuli. The stimuli were; surgical wound, talcum powder, Freund's complete adjuvant (FCA), a bacterium Aeromonas hydrophila, and spores of fungus Aphanomyces invaderis. Following exposure to these stimuli, fish were sacrificed over a period of time, and sequential tissue samples were processed for histopathological examinations. The surgical wounds at 27°C, re-epithelialized at 4 hours. Macrophage infiltration began at 2 hours, and myophagia at 6 hours. Fibroplasia and muscle regeneration were initiated at 2 days. After 16 days epidermis was normal and dermis was completely linked. The wounded area restored its main components by 16 to 24 days after wounding. Injection of talcum powder at 26.5°C, and FCA at 24°C, produced chronic granulomatousin flammatory reaction. The following events started in both experiments at the same time; myophagia at 6 hours, macrophages had changed into epithelioid cells, active fibroplasia and muscle regeneration at 3 days. Regenerated muscles filled the defects by 14 to 28 days post-injection (p. i. ). Langhans and foreign body giant cells, were observed after 3 days in talc and 4 days in FCA experiment. New capillaries formed at 3 days in talc and 2 days in FCA study. At the end of the experiments (42 days) the encapsulation of the irritants was very advanced, and the granulomata were entirely surrounded by normal muscle tissue. Inoculation of the Aeromonas hydrophila at 27.5°C, provoked a lethal acute inflammatory response within 48 hours. The surviving fish showed well developed capacity for dealing with bacteria. An ulcerative wound developed by 48 hours in the surviving fish. Polymorphonuclear cells (PMNs) were observed at 1 hour p.i . and remained up to 7 days. PMNs were one of the dominant inflammatory cells and participated in myophagia and micro-abscess formation. The acute inflammation then developed into chronic inflammation characterised by fibroplasia which was active at 5 days. Process of wound healing began and developed by 5-10 days and was completed by scar formation at 28 days. A chronic inflammatory response occurred after inoculation of spores of the fungus Aphanomyces invaderis at 27°C. Limited growth of the fungus in tissue occurred in the early stages p. i. but was then halted by fish's defence mechanisms. Macrophages had changed into epithelioid cells at 3 days p. i. Presence of Langhans, foreign body and intermediate giant cells, muscle regeneration, fibroplasia, and vascularization also started at 3 days. Developing granulomata formed by 10 days, and fully matured granulomata were observed by 18 days.
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