An Exotic Nematode Parasite

We investigated reports from commercial fishers of parasitized American eels (Anguilla rostrata) in the Patuxent River (located in the mid-Chesapeake Bay) and discovered that some eels were infected with an exotic swim bladder nematode, Anguillicola crassus. Here, we (1) describe the dispersal of this blood-feeding nematode, endemic to the Japanese eel (A. japonica), in Europe and North America; (2) discuss what is known of the effects of this parasite on eels; (3) summarize current knowledge of the life cycle and identification of this parasite; and (4) present new data on the range of A. crassus in the eastern United States. We examined the swim bladders of 329 American eels from 4 sites in the midand upper Chesapeake Bay as well as 150 eels from 4 sites in the Hudson River in New York. Prevalence ranged from 10% to 29% in the Chesapeake Bay and from 0% to 12% in the Hudson River. Maximum intensity of infection was 24 for Chesapeake Bay eels and 3 for Hudson River eels. We urge our U.S and Canadian colleagues to examine American eels for A. crassus to assess the dispersal of this parasite in eastern North America. A important consequence of deliberate or accidental introductions of exotic species is dispersal of the parasites carried with them. Typically, indigenous species are more susceptible to disease caused by introduced parasite species than are the host species that transport pathogens into a new habitat, presumably because native species lack adaptations for resistance that are acquired only after long periods of parasite-host coevolution. In the Hudson River and Chesapeake Bay, we have discovered one such exotic parasite (Anguillicola crassus) a nematode that infects swim bladders of anguillid species of eels. Prior to 1980, A. crassus occurred only in east Asian countries, infecting the native Japanese eel (Anguilla japonica) and the introduced European eel (A. anguilla) (Moravec 1992). In the early 1980s, A. crassus infections were noted in European eel populations. Scientists presumed the introduction was due to shipment of Japanese eels from Asia to aquaculture facilities in Germany, where the nematode first was observed in 1982 (Koie 1991). Since then, A. crassus also has been recorded in the Netherlands, Belgium, Spain, Portugal, France, England, Denmark, Italy, Greece, the former Yugoslavia, Austria, the Czech Republic, Hungary, Poland, Sweden, Estonia, Russia, and Egypt (Hoglund and Thomas 1992; Nagasawa et al. 1994). Ann M. Barse is an assistant professor at the Richard A. Henson School of Science and Technology, Department of Biological Sciences, Salisbury State University, Salisbury, MD 21801; 410/543-6073; [email protected]. David H. Secor is an assistant professor at the Chesapeake Biological , Laboratory, University of Maryland Centerfor Environmental Science. 6 * Fisheries In February 1995, Fries et al. (1996) reported that the Texas Parks and Wildlife Department found A. crassus in the swim bladders of 8 of 23 eels from a Texas aquaculture facility, although the identity of the host species was not confirmed. Subsequently, these authors examined swim bladders of 30 wild American eels (Anguilla rostrata) collected from Winyah Bay, South Carolina, and several Texas rivers for the presence of A. crassus. Only a single Winyay Bay eel was infected, representing the first confirmed record of A. crassus for this anguillid host. In spring 1997, local watermen alerted us that American eels in the Patuxent River (a tributary in the midChespeake Bay) contained numerous "worms," which we identified as A. crassus. Subsequent sampling revealed that American eels infected with A. crassus were present in several Chesapeake Bay and Hudson River localities (Table 1). Because juvenile stages of A. crassus live in the swim bladder wall, and we enumerated only those worms living in the swim bladder lumen, these data underestimate the true prevalence (% of eels infected) and intensity (number of nematodes per eel) of infection. We suspect that this nematode parasite has dispersed widely among North American Atlantic coast rivers and estuaries. A. crassus Life Cycle The life cycle of A. crassus (Figure 1) includes the eel definitive host, a crustacean intermediate host (required for development), and small fish as paratenic (= transport) hosts (De Charleroy et al. 1990; Moravec et al. 1994). Only eels of the genus Anguilla can serve as final hosts (where the parasite reaches sexual maturity) of all nematodes in the genus Anguillicola (Nagasawa et Vol. 24, No. 2 MR-PW Ki^Kl KIA-riliC Cnr'f-1r RAAP.1A1-rRn rK1-