A large number of parasites are known to infect the zander's skin, eyes and internal organs. Its gastrointestinal tract can host the nematode Anisakis, which can be transmitted to humans if the fish is smoked, fried or otherwise cooked at temperatures lower than . The zander is also a vector of the trematode Bucephalus polymorphus and may have been responsible for spreading the parasite to some French river systems during the 1960s and 1970s, leading to decreases in populations of native cyprinids. Recorded predators of the zander include other zanders, as well as European eels (Anguilla anguilla), Northern pike, European perch, the wels catfish (Silurus glanis) and the Caspian seal (Phoca caspia). Use by humans The zander is considered one of the most valuable food fish native to Europe. It is esteemed for its light, firm but tender meat with few bones and a delicate flavour. Although it is not generally bred for food, its adaptability makes zander fishery quite sustainable. Indeed, in some regions release of young zanders is restricted, as natural stocks already provide a sufficient supply for the market, while boosting the population of this large predator would have an adverse effect on populations of its prey. Zander is especially well suited for fish fillets. It can also be served whole, baked, smoked or cooked. In some culinary circles, zander is appreciated even more highly than salmon. Even the offals can be cooked into consommé. In 2004, it was revealed that some restaurants in the Minneapolis-St. Paul area of Minnesota were serving imported zander instead of the closely related North American walleye (the state fish, and a popular food in the region). While zander and walleye are almost indistinguishable by taste, the restaurants were selling the European fish under the name "walleye", which is an illegal practice. An investigation by the U.S. Food and Drug Administration followed. In Ohio, many restaurants were caught using juvenile zander fillets in the 40 to 80 gram range in place of the Lake Erie yellow perch. Shortages of the perch along with skyrocketing prices caused wholesalers and restaurants to use the juvenile zander for popular "pike perch fillets". In Finland, as a conservation measure, the law regulates the minimum size of zander considered mature enough to be eaten. In July 2009, in a rare occurrence, a zander bit bathers swimming in the Swiss part of Lake Maggiore, sending two people to