Physiological response of hybrid striped bass subjected to Photobacterium damselae subsp. piscicida

This study consisted in the analysis of the physiological response through metabolic, immune and molecular indicators over time in the hybrid striped bass (HSB) affected by pasteurellosis, a bacterial infection caused by Photobacterium damselae subsp. piscicida (PDP). Affected fish showed statistically lower hematocrit, glucose values tended to increase and lactate levels decreased, compared to control values. Regarding the immunological parameters studied, lysozyme and complement showed a reduced response after the bacterial infection. Cortisol, a main indicator of stress response showed that animals were stressed during the first weeks of infection, reaching a 2.5-fold increase. Tissue glucocorticoid receptor (GR) expression was also analyzed to test its responsiveness in front of bacterial infection in several tissues and also its efficiency as an early predictor of health state in fish under infection by PDP. The GR expression was time-specific for each tissue and showed an earlier response in liver, adipose tissue, intestine and head kidney. These alterations suggest a chronic stress situation characterized by a metabolic, energetic and immune imbalance in affected HSB.