Can freshwater and saltwater fish pass disease to each other?

[ralphie16]

Can freshwater and saltwater fish pass disease to each other?

Example 1: Using the same buckets, nets, etc.

Example 2: Take a freshwater black molly. Acclimate him to saltwater. Do I still have to QT him or can he go directly in saltwater display without any fear of disease transfer?

I understand saltwater ick and freshwater ick are two different species but how about the other diseases common in our hobby?

[leebca]

There are some bacteria that can make the transition, but almost all 'higher' pathogens can't go from one environment into the other.

Taking the Molly as an example. If the fish is coming from freshwater, then it can go into the saltwater, with proper acclimation, without concern of having to quarantine the fish for pathogens. Still, if there is any concern about injury, or the fish not eating, it is better to quarantine the fish.

Once the Molly is in the saltwater, it can be attacked and it can contract Marine Ich and other marine fish diseases.