The injured man was attending a crayfish party -- a traditional Swedish celebration at which crayfish is eaten -- in Stockholm's Skansen Aquarium, when he was bitten on the arm by a crocodile.
The man was giving a speech while standing on a rock in a restricted area of the facility.
"He had his arm over the glass barrier, which is about two meters high. One of the Cuban crocodiles saw it and came and just jumped up and grabbed his lower arm," Jonas Wahlström, owner of the Skansen Aquarium, told CNN.
"Luckily there were three medical doctors at the party, so they took care of him and stopped the blood," he added. "The ambulance came and took him to hospital."
The man sustained injuries to his lower arm and hand.
"The crocodile lost its grip after 10 seconds," Wahlström added.
The snappy reptile is one of two Cuban crocodiles originally given to a Russian cosmonaut by Castro in the 1970s.
The cosmonaut took the animals back to Moscow, and they were eventually brought to Sweden by Wahlström.
The aquarium has bred many Cuban crocodiles from the pair since they arrived at the facility in 1981, and has reintroduced some of the animals to Cuba. Cuban crocodiles are thought to be critically endangered.
"The Skansen Aquarium are taking further actions to prevent this from happening again. Our thoughts are with the man, and his family, who are affected by this very tragic accident," the aquarium said in a statement.
A spokesperson for Stockholm police told CNN that the police were investigating the incident.