The troubled ferry has returned to the Troon-Arran route though almost a third of CalMac's fleet remains out of service.
Analysis confirmed the Usutu virus in birds found dead in Arran.
MV Isle of Islay has been placed on standby after MV Glen Sannox was taken out of service due to an engine fault.
A warning light for one of the ship's main engines means sailings have been cancelled since Monday afternoon.
The two other ferries which normally serve the Arran route have been undergoing maintenance.
Ferries and flights are cancelled and roads closed as the latest named storm sweeps across Scotland.
MV Caledonian Isles, which serves the Arran route, had been sidelined by a series of faults, with the bill reaching nearly £12m.
The MV Glen Sannox is to make its first scheduled passenger voyage between Troon and Arran early on Monday.
MV Glen Sannox has started carrying passengers between the Scottish mainland and the island of Arran.
