Phagocytosis, complement lytic activity and opsonization capacity of rainbow trout plasma as well as the ability of phagocytes to recognize foreign particles were studied at different temperatures. Respiratory burst (RB) activity and opsonization capacity were assessed as chemiluminescence emission from diluted whole blood of fish which were acclimatized for 57 days at temperatures between 5 and 20 degrees C. RB activity was higher at higher acclimatization and in vitro assay temperatures. The peak time of RB was significantly delayed in fish kept at lower temperatures (5-10 degrees C) as compared to fish kept at 15 or 20 degrees C temperatures. Opsonization capacity of plasma decreased in fish acclimatized at low temperatures and was also affected by in vitro assay temperature. The importance of glucan receptors in RB activity increased in fish kept at higher temperatures and was also affected by the in vitro assay temperature. The higher acclimation temperatures increased the lytic activity of both total and alternative complement pathways.
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