Tipped as this year's must-see Christmas movie for kids, Disney's Finding Nemo hits German cinema screens Thursday. German experts fear the computer animation film, already a smash hit in the U.S., could unleash an exotic fish craze across the country. But parents should be warned -- the German Nature Protection Office has issued a statement saying that "plenty of animals make suitable pets but deep sea fish are not among them." Its president, nature protection expert Hartmut Vogtmann, says that clownfish -- the star of the film -- should only be kept by experienced fish owners in properly equipped seawater aquariums, adding that their upkeep is costly, time-consuming and demanding. Aquariums might be figuring high on this year's Christmas wish-lists, but according to Hamburg-based environmental organization Save the Rainforest, the sudden demand for tropical fish is a serious threat for endangered species.