Physiological and Cellular Stress Responses of Juvenile Rainbow Trout to Vibriosis

Abstract

Juvenile rainbow trout Oncorhynchus mykiss were experimentally infected by intraperitoneal injection with 10⁵ colony-forming units (cfu) of Vibrio anguillarum. The disease was followed for 8 d, and similar temporal trends were observed between the progressive increase in viable cfu in the blood and plasma cortisol concentration. Plasma cortisol levels increased as the pathogen load increased; maximum levels occurred 24 h before both the highest levels of pathogen in the blood and any clinical signs of disease. Levels of stress protein 70 (SP70) in liver and head kidney tissues increased significantly during disease progression. The peak in liver tissue SP70 levels corresponded to that of the plasma cortisol levels; head kidney SP70 reached peak levels 24 h later. The significant changes in plasma protein and plasma lysozyme levels also corresponded to those in SP70. Plasma glucose levels, plasma ion concentrations ((Cl^–), (Mg²⁺), and (Ca⁺)), and changes in hematocrit and hemoglobin are also described in response to disease progression.