The Coast Guard was called to the vessel after the mariners experienced possible carbon monoxide poisoning and required medical assistance.
Officials say the boat was in the Atlantic, about 11 miles east of the Indian River Bay, near Bethany Beach, at the time of the incident.
Two of the victims were taken to the Coast Guard station; the other three were taken by the Lewes Fire Department boat crew to the Bethany Fire Department.
"The Coast Guard routinely trains to provide assistance to the public in a variety of conditions," Chief Jennifer Lambert, command duty officer at the Sector Delaware Bay Command Center, said in a statement. "Today is an example of how effective training makes all the difference."
Delaware Fish and Wildlife, Department of Natural Resources and Delaware state troopers also provided assistance.