“…Histological indicators of gill disease include hypertrophy and hyperplasia of the epithelial and mucus cells, presence or absence of mast cells, lymphocytic and eosinophilic granular cell (EGC) infiltration, hyperemia and necrosis of gill tissue, and sequential progression of histopathology lesions (Ferguson et al, 1992;Dyková and Novoa, 2001;Bermingham and Mulcahy, 2004;Andrews et al, 2010;Saraiva et al, 2015). A disadvantage of histopathology is the subjective nature of interpretation, and a number of workers have devised evaluation schemes similar to those used to assess gross lesions to transform qualitative histological observations into semi-quantitative indices (Bernet et al, 1999;Mitchell et al, 2012;de Lima Cardoso et al, 2018). Behavioral changes and clinical signs, such as "coughing, " gasping, and excessive mucus production can indicate direct branchial tissue irritation or damage, and flared opercula and gilling can indicate a reaction to adverse environmental conditions (Roberts and Smith, 2011).…”