Studies on the inflammatory response of the striped snakehead Channa striatus (Fowler)

Abstract

Experiments were carried out to define the cellular response of snakehead fish, Channa striatus (Fowler), to integumental ulceration: chronic granulomatosis associated with the standard irritant Freund's adjuvant; bacterial septic abscessation due to Aeromonas hydrophila , and focal exposure to the aquatic phycomycete Achlya debaryana. Following exposure, the pathogenesis of the resultant lesion was followed by means of histopathologlcal examination of sequentially sampled specimens. In the case of integumental ulceration, small artificially induced wounds had re-epithelialized within the remarkably short space of 2-3 hours after incision. Large numbers of macrophages were found throughout the degenerated muscle area at 4-5 hours but had completely disappeared from the area of defect by day 6-12. Small numbers of polymorphonuclear leucocytes were observed only at the very earliest stage after wounding. The wounded site was restored to normal condition by around 21-28 days. Chronic granulomata were invoked by injection with Freund’s complete adjuvant. Macrophage infiltration was particularly active in the early stages after the inoculation and started to decrease by day 21. It started to take on an epithelioid configuration within 24 hours of its development. Fibrosis and vascularization were seen at about the same time around day 4.The regeneration of myofibres had strongly developed by day 6 and the new muscle bundles had replaced the area of fibrosis almost completely by the 28th day. The granulomata lesions were still extant, albeit in a very modified, and highly fibrosed form, by the end of the experiment (11 weeks).The acute inflammatory response was demonstrated in the snakehead by injection with the bacterium, Aeromonas hydrophila. An ulcerative wound developed by day 2 after the inoculation. PMN showed a marked response to the bacterial infection and had infiltrated into the inflammatory area by the second hour after the injection. Bacterial colonies, found in the inflammatory area, were very closely related to these PMN clusters. Fibrosis started to encapsulate the necrotic area around 30-36 hours post injection. The lesion began to heal by day 7 to 10 and the healing process was completed around day 28. A very mild inflammatory response occurred in the snakehead injected with the fungus, Achlya debaryana. Some infiltrated PMN and lymphocytes migrated into the inoculated site at the early stages of the experiment, but macrophage activity dominated in the necrotic muscle area. Fibrosis, new capillaries, and regenerated muscle fibres were found by day 3-4 and the lesion was completely healed around day 6.