Evaluation of fixation methods for demonstration of Neoparamoeba perurans infection in Atlantic salmon, Salmo salar L., gills

• Published in: Journal of Fish Diseases
• Main Authors: Cadoret, K, Bridle, A R, Leef, M J, Nowak, B F
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2013
• Subjects: Almo; Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1111/jfd.12078; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjfd.12078; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfd.12078

Abstract Formaldehyde‐based fixatives are generally employed in histopathology despite some significant disadvantages associated with their usage. Formaldehyde fixes tissue by covalently cross‐linking proteins, a process known to mask epitopes which in turn can reduce the intensity of immunohistochemical stains widely used in disease diagnostics. Additionally, formaldehyde fixation greatly limits the ability to recover DNA and m RNA from fixed specimens to the detriment of further downstream molecular analyses. Amoebic gill disease ( AGD ) has been reliably diagnosed from histological examination of gills although complementary methods such as in situ hybridization ( ISH ) and polymerase chain reaction ( PCR ) are required to confirm the presence of N eoparamoeba perurans , the causative agent of AGD . As molecular techniques are becoming more prevalent for pathogen identification, there is a need to adapt specimen collection and preservation so that both histology and molecular biology can be used to diagnose the same sample. This study used a general approach to evaluate five different fixatives for Atlantic salmon, S almo salar L ., gills. Neutral‐buffered formalin and seawater Davidson's, formaldehyde‐based fixatives commonly used in fish histopathology, were compared to formalin‐free commercial fixatives PAX gene ® , H istoChoice™ MB * and RNA later™. Each fixative was assessed by a suite of analyses used to demonstrate AGD including routine histochemical stains, immunohistochemical stains, ISH and DNA extraction followed by PCR . All five fixatives were suitable for histological examination of A tlantic salmon gills, with seawater D avidson's providing the best quality histopathology results. Of the fixatives evaluated seawater D avidson's and PAX gene ® were shown to be the most compatible with molecular biology techniques. They both provided good DNA recovery, quantity and integrity, from fixed and embedded specimens. The capacity to preserve tissue and cellular morphology in addition to allowing ...