Interesting smorgasbord of diseases the salmon feedlots are breeding...
Gill Disease (Proliferative Gill Inflammation
Epitheliocysts/Chlamydia & Amoebic Gill Disease)
Paranucleospora theridion
Parvicapsulosis (Parvicapsula pseudobranchicola/Paranucleospora theridion)
Gyrodactylus (‘Salmon Killer’)
Furunculosis (Aeromonas salmonicida)
Infectious Hematopoietic Necrosis (IHN)
Viral Haemorrhagic Septicaemia (VHS)
Cardiomyopathy Syndrome (CMS)
Heart and Skeletal Muscle Inflammation (HMSI)
Plasmacytoid Leukemia (Marine Anemia)
Bacteria Kidney Disease (BKD)
Myxobacterial Infection (Piscine Tuberculosis)
Spironucleosis (Spironucleus salmonicida)
Francisella (Francisellosis)
Yersinia ruckeri (Yersiniosis/Enteric Redmouth/ERM)
Flavobacterium psychrophilum (Bacterial Cold Water Disease/Rainbow Trout Fry Syndrome)
Vibriosis (Cold Water Vibriosis/Hitra Disease)
Moritella Vicosa (Winter Ulcer)
Hemorrhagic smolt syndrome (HSS)
Mad Fish Disease
Botulism (Clostridium botulinum)
Parasitic Meningitis
Costia (Ichthyobodo species)
Tapeworm (Diphyllobothriasis)
Microsporidian encephalitis
Nephrocalcinosis (urolithiasis)
Malignant Intestinal Tumours
Desmozoon lepeophtherii (Paranucleospora theridion) & Autumn Disease and Salmonella.
It's easier to understand why they need to use all those antibiotics.
Edit: I missed Infectious Salmon Anaemia (ISA) and Infectious Pancreatic Necrosis (IPN)