Myocarditis, called cardiomyopathy syndrome CMS is a disease in farmed Atlantic salmon caused by the piscine myocarditis virus (PMCV). "Currently no commercial vaccine available against PMCV, meaning the disease itself is the cause of myocarditis, not a reaction to a vaccine." Really?

https://pmc.ncbi.nlm.nih.gov/articles/PMC3889245/