2 months is not a long time, it can take many months for an infectious agents to reproduce enough for it to become lethal (infectious dose). This is why a find the idea that a few week quarantine for fish is pathetic at best.
And as Tom said, there are species specific viruses and bacteria, and some that will be more virulent to some fish first, and or/other more pelagic species later on.
Many viruses take time to morph or become infective, take bird the flu transition to humans as an example.
Species that are substrate huggers are often very vulnerable to vectors such as bacteria or viruses that find detritus a convenient medium to reside.
And as Tom said, there are species specific viruses and bacteria, and some that will be more virulent to some fish first, and or/other more pelagic species later on.
Many viruses take time to morph or become infective, take bird the flu transition to humans as an example.
Species that are substrate huggers are often very vulnerable to vectors such as bacteria or viruses that find detritus a convenient medium to reside.
