Carnival Cruise Line is set to welcome two more ships from sister line Costa Cruises.As part of a new “Costa by Carnival” brand-within-a-brand experience that the line announced Wednesday, 4,208-passenger Costa Venezia and 4,232-passenger Costa Firenze will move to the Carnival fleet in 2023 and 2024, respectively.Costa Venezia and Costa Firenze — two of Costa Cruises’ four newest vessels — will join the 2,260-passenger Costa Luminosa in transferring to Carnival. Costa Luminosa is scheduled to move to Carnival’s fleet this September with a rebrand as Carnival Luminosa.However, the former two ships, which have the same layout as Carnival’s Vista-class vessels (Carnival Vista, Carnival Horizon and Carnival Panorama), will be operated without any physical rebranding. That means the ships will retain their original names and interior design aesthetic. As a result, passengers can enjoy Italian ambiance, combined with the food, entertainment, service and value they’ve come to expect from Carnival.For more cruise news, guides and tips, sign up for TPG’s cruise newsletter.“This is an exciting opportunity for us to operate two additional beautiful Vista-class ships in the [United States] and bring a unique experience to those who love the culture, food and vibe of Italy,” Carnival President Christine Duffy said in a statement. “There are lots of ways we plan to create an immersive fun experience for our guests who choose to sail on these ships, which have beautiful Italian-design elements, dining and retail that will deliver Carnival fun [and leverage] the spirit of Italy from our sister line Costa Cruises.“Costa Venezia has a design similar to Carnival’s Vista-class ships. (Photo courtesy of Costa Cruises)This might be the closest the cruise industry has come to a codeshare – when airline brands form a partnership to operate flights on behalf of each other in an effort to cover more markets and sell more tickets.Costa Venezia and Costa Firenze will continue to sail their scheduled itineraries for Costa until they move over to the Carnival fleet. The line has not yet released U.S.-based itineraries for either vessel, but Carnival has shared that the former will sail from New York City, and the latter will be based in Long Beach, California, near Los Angeles.Sailings on the vessels will be crewed, operated and sold by Carnival, which means that passengers who book voyages on the ships after they relocate will earn loyalty credit toward Carnival’s VIFP Club program, rather than Costa’s C|Club.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.In announcing the move, Carnival didn’t give a reason for the vessel transfer between the brands or elaborate on why the ships would continue to operate under the Costa monikers. But the announcement comes as the line’s parent company, Carnival Corporation, is in the midst of making changes to the fleets at several of its brands as it charts a path to recovery.Carnival Corporation is the parent company of nine brands including Carnival, Costa, Princess Cruises, Holland America and Seabourn, all of which paused operations for months after the COVID-19 pandemic began in early 2020 and have only been slowly resuming normal service.Carnival Corporation in March said occupancy on its ships was only at 54% during the first quarter of the year, far lower than normal. Only about 60% of the company’s fleet capacity was back in operation in the first quarter.As a result of the shutdown and slow restart, Carnival Corporation has lost billions of dollars over the past two years, forcing it to take on an enormous amount of debt. The company’s debt load was $34.9 billion at the end of the first quarter.Wednesday’s announcement came just two days before Carnival Corporation was scheduled to discuss its financial situation in a conference call with Wall Street analysts.Planning a cruise? Start with these stories:The 5 most desirable cabin locations on any cruise shipThe 8 worst cabin locations on any cruise shipA quick guide to the most popular cruise lines21 tips and tricks that will make your cruise go smoothly15 ways cruisers waste money12 best cruises for people who never want to grow upWhat to pack for your first cruise