Table 1. Overview of the prevalence of ISA virus positive wild salmonids sampled in rivers in Trøndelag (Orkla, Gaula, Stjørdalselva, Steinkjærelva, Namsen) and Finnmark (Altaelva).
Salmon and trout were also collected in the sea using fish traps in the fjords; Agdenes, Kvaløya, Namsfjorden and Altafjorden (Fig 1). Gill tissues from all fish sampled were tested for presence of ISA virus.
| 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | Total | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Species/Location | N | Pos—% | N | Pos—% | N | Pos—% | N | Pos—% | N | Pos—% | N | Pos—% | N | Pos—% |
| Salmo salar | ||||||||||||||
| Agdenes | - | - | 204 | 5–2.5 | 43 | 4–9.3 | 60 | 2–3.3 | 67 | 6–9.0 | 56 | 7–12.5 | 430 | 24–5.6 |
| Orkla | 70 | 4–5.7 | 70 | 2–2.9 | 72 | 4–5.6 | 28 | 0–0.0 | 27 | 0–0.0 | - | - | 267 | 10–3.7 |
| Gaula | 75 | 3–4.0 | 149 | 1–0.7 | 46 | 5–10.9 | 76 | 0–0.0 | - | - | 22 | 0–0.0 | 368 | 9–2.4 |
| Stjørdalselva | 74 | 2–2.7 | 16 | 2–12.5 | 50 | 0–0.0 | 12 | 0–0.0 | 60 | 3–5.0 | 78 | 2–2.6 | 290 | 9–3.1 |
| Stenkjærelva | - | - | - | - | - | - | - | - | 58 | 0–0.0 | 35 | 0–0.0 | 93 | 0–0.0 |
| Kvaløya | - | - | - | - | - | - | - | - | - | - | 60 | 6–10.0 | 60 | 6–10.0 |
| Namsfjorden | - | - | - | - | 94 | 20–21.3 | 62 | 4–6.5 | 58 | 22–37.9 | 60 | 18–30.0 | 274 | 64–23.4 |
| Namsen | 121 | 0–0.0 | 95 | 2–2.1 | 49 | 1–2.0 | 60 | 1–1.7 | 60 | 3–5.0 | 60 | 2–3.3 | 445 | 9–2.0 |
| Altafjorden | - | - | - | - | - | - | - | - | 41 | 2–4.9 | 38 | 8–21.1 | 79 | 10–12.7 |
| Altaelva | - | - | - | - | - | - | 80 | 5–6.3 | 81 | 4–4.9 | 60 | 3–5.0 | 221 | 12–5.2 |
| Salmo trutta | ||||||||||||||
| Agdenes | - | - | 18 | 2–11.1 | 1 | 0–0.0 | 32 | 0–0.0 | 15 | 1–6.7 | 14 | 0–0.0 | 80 | 3–3.8 |
| Kvaløya | - | - | - | - | - | - | - | - | - | - | 8 | 1–12.5 | 8 | 1–12.5 |
| Namsfjorden | - | - | - | - | 2 | 1–50.0 | 1 | 0–0.0 | 2 | 0–0.0 | 7 | 0–0.0 | 12 | 1–8.3 |
| Altafjorden | - | - | - | - | - | - | - | - | 12 | 2–16.7 | 35 | 2–5.7 | 47 | 4–8.5 |