Priority Diseases of Farmed Salmon

(article 2020) deaths at all new high - suffer from wide range diseases = crowded conditions - high levels of stress = caused by sea lice infesttation and its treatment, handling and crowding = increasingly susceptable to infection - Amoebic Gill Disease ~ causes resp problems and death through asphyxiation ~ major mortalities scotland - 50% losses on salmon farms - 2019 £3 bilion fish farming firm Mowi reported deaths of around 700,000 salmon in just 3 months diseases/sea lice infestations among top reasons cited for huge no. deaths • but not clear of exact cause

• salmon pox virus • proliferative gill disease • cardiomyopathy syndrome, • pancreas disease, • anaemia, • fungus • bacterial challenges • treatment losses (misuse chemicals, de-licing machines), • handling errors, • algal booms, • jelly fish, • seals, • poor water quality • oxygen shortage

Areas of action • information flow and transparancy • gill health • sea lice • cleanerfish • production cycle and on-farm management • licencing regime and medicine use • climate change and ocean acidification • require commitment and resource from all of its partners • interaction with no. related activities inc farmed wild fish interactions, help inform future development of framework and working activities

• Notifiable diseases – e.g. Infectious salmon anaemia, Bacterial kidney disease (BKD) = info from marine scotland website/ceefax • Sea lice infection – Sea lice infect salmon skin and if not controlled they can cause lesions and secondary infection • Viral induced cardiomyopathies – Group of diseases, cause similar pathologies. No control measures available except for salmon alphavirus • Gill health problems – complex disease scenario, contributed by many pathogens. (global warming) bac, virus, parasites cause probs similtaneously. compromise resp system

• Sea lice are copepods (Crustaceans) • Occur naturally in coastal and open ocean populations of fish, as well as in freshwater environments • There are over 300 species of lice, most of which are parasitic on fish • Natural parasite of wild and farmed sea-caged Atlantic salmon ( Salmo salar) ~ Lepeophtheirus salmonis (common) ~ Caligus elongatus

• Sea lice infestation is a major issue in many salmon producing countries • Productivity loss due to lice infestations has cost GBP 1.8 billion in Scotland alone • In Norway, the total loss caused by sea lice is equivalent to 8.81% of the industry’s total production value • welfare concern - stress, death, transmit to wild fish

2 main stages - free swimming stage - parasitic stage 2 free swimming stages - noplius stage x2 - copepodid (infective stage) Parasitic stages - chalmus x4 stages (static = parasite attatched to and feed on fish but not mobile) - pre-adult x2 (mobile) - adult (determine if male or female) ~ female = long paired eggstrings at lower end

Industry Requirements • Satisfactory measures – control prevention and reduction • Legislative requirements – ‘2008 Record Keeping Order’ • Industry Code of Good Practice Industry Code of Good Practice • weekly counts 25 fish (5 fish from 5 cages) average no adult female lice exeeds 2 = manditory to report to fish inspectorate • suggested trigger 0.5 (Feb-June) 1 (July-Jan) Ls adult female • management agreements • appropriate training • good practice in the use of medicinal products

• mortalities • runting • post havest condemnation

- Salmonid alphavirus (SAV) ~ Salmon pancreas disease (SPD or PD) - Piscine Myocarditis virus (PMCV) ~ Cardiomyopathy syndrome (CMS) ~ inflamation of heart - Piscine Reo virus (PRV) ~ Heart and Skeletal muscle inflammation (HSMI)

• mortalities - range from 5-50% of stock • runting - poor growth • post havest condemnation - pale musculature or black colour discolouration ~ muscle inflamation, ~ macrophages gather around lesions, ~ preaching pignemted macrophages = melana macrophages

• alpha virus • RNA +ve sense ssRNA (group 4) • pancreas, heart, skeletal muscle • post smolts and adults 1st and 2nd year • lethargy and off food, faecal casts = see large amount of undigested food, white in colour, apear as tails from animal

• Piscine reovirus • RNA segmented linear dsRNA (group 3) • heart and skeletal muscle • post smolt 1st year in sea • sudden death, ascites in PM = accumulation of fluid in abdominal cavity

• toti virus • RNA linear dsRNA genome (group 3) • heart and liver • sea water - smolts, post smolt and adult ~ when fish handled just before harvest = second heart failure ~ have been reported from hatchery and brood stock very recently • sudden death, flabby hearts in PM, skin haemorrhages

• sea water transfer and stay in sea for 2 years • HSMI infection 5-8 months into sea water phase ~ clinical 7-9 months • PD infection 10-12 months ~ PD clinical 11.5-13.5 months • CMS infection 14-17.5 months ~ CMS clinical 16-18 months (all diseases virus induced cardiomyopathies) • now at seawater transfer, serious infection at early stages in sea water and hatchery (no clinical signs at hatchery) with IPNV infection • pd also canged as can infect fresh water as well as sea water fish

• next generation sequencing to map genetic diversity and geographic distribution 7 alphavirus • SAV3 only found in norway • SAV 2 used to be a freshwater varient, • but study suggests that SAV subtypes are circulating in between geographical boundries • circulation of multiple SAV subtypes on the same fish farm and abundant within-subtype genetic diversity in all studied samples • co-infections of two SAV subtypes detected in individual wild host fish