It is not clear how the animal managed to gain access to the ship while it was docked at the English port city.
The zoo said initial examinations suggested the fox appeared to be in good health and that additional results from a separate routine health screening were pending.
“He seems to be settling in well,” Keith Lovett, the zoo’s director of animal programmes, told the Associated Press. “It’s gone through a lot.”
A spokesperson for Associated British Ports (ABP) Southampton said: “The Port of Southampton handles everything from cars to containers to cruises, but even we were surprised to find a fox had booked itself a transatlantic crossing.
“Clearly it fancied swapping the Solent for the Staten Island Ferry. Though next time we’d recommend it considers the Queen Mary 2, which offers the Southampton to New York route with considerably more comfort!”
According to the Bronx Zoo, red foxes are among the most widespread carnivorous mammals in the world.
Known for their reddish coat and white-tipped bushy tail, they are found across Europe, Asia, North America and parts of Africa.
The red fox’s remarkable adaptability allows them to thrive in environments ranging from forests and grasslands to urban areas, the zoo said, feeding off everything from fruits to rodents.