Effects of the ectoparasite Caligus rogercresseyi on Salmo salar blood parameters under farm conditions

Abstract

Between 2006 and 2009, the Chilean salmon industry suffered a major sanitary crisis caused by outbreaks of infectious salmon anemia virus and Caligus rogercresseyi. Additionally, Piscirickettsia salmonis, the causative agent of piscirickettsiosis, and the parasite C. rogercresseyi continue to impact the salmon industry. This study evaluates the effects of both C. rogercresseyi infestation and P. salmonis infection concurrently on the blood parameters of Salmo salar (Atlantic salmon) under field conditions, providing an estimated parasite threshold at which the least impact occurs on host physiology. The presence of P. salmonis and C. rogercresseyi increased S. salar hematocrit, plasma glucose, and pCO2 levels but decreased hemoglobin and pO2 levels. Significant threshold values of parasite abundances were estimated for glucose, hematocrit, hemoglobin, and lymphocytes. This is the first study to evaluate the effects of C. rogercresseyi on S. salar physiology and to provide estimated abundance threshold values under farm conditions. Although the threshold estimations will likely be of great value for surveillance and control programs, they are an initial approximation that requires further confirmation. The prevalence of C. rogercresseyi and P. salmonis in Chilean salmon farms necessitates further research on the development and establishment of on-farm pathogen indicators. Statement of relevanceThe manuscript is the first study of C. rogercresseyi effects on S. salar blood parameters on farm conditions, with an estimation of abundances thresholds values. This information is of great relevance in an integrated pest management program and S. salar welfare.