Yes - fish can harbor ich and/or velvet and be asymtomatic...but they cannot be carriers in the traditional sense as the ich MUST still go through its life-cycle to persist in the tank. That means they MUST drop, encyst hatch and re-infect their host.
As the studies on immunity show - no trophonts were detected dropping from infected fish @3 months and because of this, the life cycle cannot complete. Even at 6 months - as the temporary immunity fades (which it won't if its still encountering ich). The reproduction rate of ich is below the replacement threshold, meaning ich is on its way to extinction.
Additionally, in isolate studies - it is very difficult to get ich any isolate if ich to persist beyound 11 months - even if it is continually fed a diet of susceptiple non-immune fish...the average isolate dies off much sooner.
And finally if you could actually see ich and velvet and watch their movements - you would see what is wrong with your tank and why I keep saying - lethal ich or velvet is a symptom of a mis-configured system. If your tank has adequate flow and circulation - ich will never build to lethal levels...but I'll take that one up in another thread.
As the studies on immunity show - no trophonts were detected dropping from infected fish @3 months and because of this, the life cycle cannot complete. Even at 6 months - as the temporary immunity fades (which it won't if its still encountering ich). The reproduction rate of ich is below the replacement threshold, meaning ich is on its way to extinction.
Additionally, in isolate studies - it is very difficult to get ich any isolate if ich to persist beyound 11 months - even if it is continually fed a diet of susceptiple non-immune fish...the average isolate dies off much sooner.
And finally if you could actually see ich and velvet and watch their movements - you would see what is wrong with your tank and why I keep saying - lethal ich or velvet is a symptom of a mis-configured system. If your tank has adequate flow and circulation - ich will never build to lethal levels...but I'll take that one up in another thread.