TABLE 3.
Semi-quantitative scoring system used for histopathological examination of gill tissue in sea farmed Atlantic salmon (adapted and modified from Mitchell et al., 2012).
| Parameter | Description |
| Index criteria with scores 0–31 | |
| LH | Lamellar hyperplasia |
| LF | Lamellar fusion |
| LO | Lamellar oedema |
| CA | Cellular anomalies |
| Ancillary criteria with scores 0–31 | |
| In | Inflammation (presence of inflammatory cells outside blood vessels) |
| Eg | Eosinophilic granular cells (numbers higher than normal in gill filaments) |
| Cc | Chloride cells (numbers higher than normal and/or abnormal location) |
| Cd | Circulatory disturbances (thrombi, telangiectasis, congestion) |
| Ib | Interlamellar blood (hemorrhage) |
| Ch | Cellular hypertrophy (hydropic degeneration of lamellar cells) |
| bE | Epitheliocystis-like bacteria |
| bT | Tenacibaculum-like bacteria (mats of filamentous bacteria on lamellar surfaces) |
| Ob | Other bacteria |
| Pp | Protist parasites, Neoparamoeba-like |
| Op | Other parasites or agents |
1Scoring system 0–3, with 0 = no pathological changes, 1 = mild changes affecting < 10% of gill tissue, 2 = moderate changes affecting 10–50% of gill tissue, and 3 = severe changes affecting > 50% of gill tissue.