Distribution of ligulid tapeworms in China

A survey of ligulid tapeworms carried out from 1979 through 1985 covered 29 provinces and autonomous regions in China. Of the 25,800 fishes of 219 species that were dissected, fishes of 43 species were found to serve as second intermediate hosts. These tapeworms inflict heavy losses on freshwater commercial fisheries. Their distribution indicates 3 distinct major zones: the Qing Zang Gaoyuan is dominated by Ligula; the rest of China, with the exception of a crescent area in Guangdong Province bordering part of the southern coast down to Hainan Island, is dominated by Digramma; and a saddle-shaped corridor, north of 42?N latitude, is characterized by a mix of both genera. Schizothoracinae are the primary hosts for Ligula, of which only Gymnocypris przewalskii przewalskii (Kessler) has economic value. Digramma is predominant in Carassius auratus auratus L. in reservoirs and lakes of 3 main water systems, Heilongjiang, Huang He (the Yellow River), and Chang Jiang (the Yangtze River), and in cultured cyprinids along the lower section of Huang He as well as in bodies of water on the Loess Plateau. Generic validity of ligulids and host specificity, their infection and periodicity, and control methods are discussed. Three genera, Ligula, Digramma, and Schistocephalus, comprise the family Ligulidae. The latter genus has not been found in China. Thus the present study is confined to Ligula and Digramma. The particular mode of parasitism of the large-sized plerocercoid larvae occupying the abdominal cavity of cyprinid hosts in reservoirs and lakes is considered dangerous, inflicting heavy losses on freshwater pisciculture in China. As early as the Ming Dynasty (1368-1644 A.D.), Carassius was recommended as a delicacy for winter months because of the whitish fatty worms it contained, which northerners took as noodles (Yang Sheng, Ming). These whitish worms, though identified as ligulids in recent years, are still greatly enjoyed as a dainty dish in some provinces in China. Ligula and Digramma exhibit similar life cycles, including 2 intermediate hosts and a fishfeeding definitive host. Cooper (1918) and Joyeux and Baer (1936) listed as many as 55 species of birds and 63 species of teleost fishes that have been reported to serve respectively as definitive and second intermediate hosts. The adult matures in the intestines of the definitive hosts within 44 hr after being acquired and subsequently lays an enormous number of eggs. Dead worms are usually discharged with the feces of the host 72 hr after infection. In South China, the plerocercoid takes 8-10 mo to develop into the infectious stage and in the northwest regions it takes 2-3 yr. Received 19 March 1986; revised 7 July 1986; accepted 7 July 1986. The distribution of ligulid tapeworms is cosmopolitan. In the U.S.S.R., considerable literature exists on their occurrence as the cause of massive epizootic ligulosis, which produces serious economic loss to freshwater commercial fisheries (Agapova and Zhatkanbaeva, 1971; Lyubina, 1972; Safonov, 1972; Denisov and Vorob'ev, 1974; Kazadaev, 1974; Dubinina, 1980), and research has been carried out to meet the demand for its control (Vasilkov and Kamenski, 1970; Medvedev, 1971; Antonov, 1972; Dubinina, 1980). In England, research on ligulids has been mostly concerned with population biology, pathology, and other biological aspects (Owen and Arme, 1965; Arme and Owen, 1969; Bibby, 1972; Harris and Wheeler, 1974; Sweeting, 1976, 1977; Kennedy and Burrough, 1981). As in Yunnan Province in China, people in the Mazurian Lake area in Poland have been known t eat Ligula plerocercoids obtained from local fish (Korpaczewska, 1972). In Canada, ligulids e a higher prevalence in cyprinids than in percids (Lawler, 1964; Mahon, 1976), whereas in the United States, Ligulidae are widespread among species of perch and cyprinids (Cooper, 1918; Pitt and Grundmann, 1957; Lewellen and White, 1971). Ligula is also found in Mexico, although rarely (Lamothe-Argumedo and Cruz-R., 1970, 1972). In Asiatic countries and in the Pacific region, records show that ligulids are common in Japan (Awakura, 1975; Awakura et al., 1976) but rare in India (Natarajan, 1976) and Australia (Pollard, 1974). Ligulid tapeworms are distributed throughout most of China. Their distribution is attributed to several factors. First, the migration of pisciv-