ICES Journal of Marine Science

ICES Journal of Marine Science ICES Journal of Marine Science (2016), 73(1), 14 21. doi:10.1093/icesjms/fsv097 Contribution to the Symposium: International Eel Symposium 2014 Original Article Infection of newly recruited American eels (Anguilla rostrata) by the invasive swimbladder parasite Anguillicoloides crassus in a US Atlantic tidal creek Jennifer L. Hein 1, Isaure de Buron 2, William A. Roumillat 1,WilliamC.Post 1, Allan P. Hazel 1, and Stephen A. Arnott 1 * 1 South Carolina Department of Natural Resources, Marine Resources Research Institute, 217 Fort Johnson Road, Charleston, SC 29422, USA 2 Department of Biology, College of Charleston, 58 Coming St, Charleston, SC 29401, USA *Corresponding author: tel: +1 843 953 9794; fax: +1 843 953 9820; e-mail: arnotts@dnr.sc.gov Hein, J. L., de Buron, I., Roumillat, W. A., Post, W. C., Hazel, A. P., and Arnott, S. A. Infection of newly recruited American eels (Anguilla rostrata) by the invasive swimbladder parasite Anguillicoloides crassus in a US Atlantic tidal creek. ICES Journal of Marine Science, 73: 14 21. Received 2 December 2014; revised 3 May 2015; accepted 5 May 2015; advance access publication 1 June 2015. Little is known about the infection status of glass eel and elver stages of the American eel Anguilla rostrata by the invasive swimbladder parasite Anguillicoloides crassus. This study examined infection by adult and larval A. crassus in glass eels (n ¼ 274) and elvers (n ¼ 199) collected during March December 2013 from an eel ladder at a dammed creek near Charleston, SC, USA. Among all the eels examined [total lengths (TLs), 34 156 mm], the prevalence (+SE), mean abundance, and mean intensity of A. crassus worms was 29.4 + 2.1%, 0.88 + 0.12, and 2.98 + 0.34, respectively. Infection by A. crassus was not detected in the earliest glass eel development stages (pigment stages 1 3), but it was detected in more advanced stages (pigment stages 4 7) and fully pigmented elvers. From March to July, parasite prevalence increased significantly with eel TL, and all eels 125 mm or longer (n ¼ 13) were infected. From August December, when fewer eels were caught, parasite prevalence was generally lower and less dependent on the eel TL. Our study demonstrates the potential risk of spreading A. crassus to new areas by transporting live glass eels and elvers. This is of particular relevance because our study site was located in the Cooper River drainage, one of the few locations in the USA that permits a glass eel harvest. Keywords: Anguilla rostrata, Anguillicola, Anguillicoloides crassus, elver, glass eel, invasive, nematode, North America, parasite, South Carolina. Introduction According to a recent stock assessment by the Atlantic States Marine Fisheries Commission (ASMFC), population numbers of the American eel Anguilla rostrata have declined substantially in the USA since the 1980s, and the stock is now considered to be depleted (ASMFC, 2012). The decline has prompted several petitions to list A. rostrata under the US Endangered Species Act. Management of American eels is complex, however, due to the species unusual catadromous life cycle, which involves spawning migrations of mature silver eels to the Sargasso Sea, oceanic transport of larval leptocephali for a year or more into coastal waters, and development through glass eel, elver, and yellow eel stages in coastal and freshwater habitats for 8 24+ years before maturity is attained. On a value per weight basis, the glass eel stages are the target of one of the world s most valuable fisheries, with prices in recent years exceeding $4000 per kg. They are used for human consumption, either directly or after live transport to aquaculture facilities for growth and have also been used to stock non-populated or extirpated eel habitats (Tesch, 2003; ICES, 2013). Harvesting of # International Council for the Exploration of the Sea 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Infection of newly recruited American eels by Anguillicoloides crassus 15 A. rostrata glass eels is currently illegal in Canada and most of the USA, except the state of Maine and the Cooper River (only) in South Carolina (SC). Harvesting of yellow and silver American eels is permitted more extensively in the USA, with eels being used mainly for human consumption or angler bait. Regulations are poorly documented elsewhere in the species panmictic range, which spans from Greenland to northern parts of South America (Avise et al., 1986). Declining numbers of A. rostrata may be linked to several factors such as varying ocean conditions, fishing mortality, barriers to migration, turbine mortality at dams, and infection by non-native (invasive) parasites. The nematode swimbladder parasite, Anguillicoloides (¼Anguillicola) crassus, hasreceivedparticular attention as an invasive parasite of anguillids (Székely et al., 2009; Vogel, 2010). Genetic evidence suggests that the parasite may have originated from Asia (Laetsch et al., 2012; Lefebvre et al., 2012b), where it infects the Japanese eel Anguilla japonica, but it was unintentionally introduced into American eels and into European eels, Anguilla anguilla (Lefebvre et al., 2012a). Eels acquire A. crassus by ingesting infected intermediate or paratenic hosts, which in North America are unknown, but in Europe and Asia include copepods and ostracods (intermediate hosts), fish (natural paratenic hosts), and amphibians, molluscs, and insects (experimentally infected paratenic hosts) (review by Moravec, 2013; Emde et al., 2014). Health issues associated with A. crassus infection in yellow and silver eel stages include anaemia (Boon et al., 1990; Ooi et al., 1996) and swimbladder damage (Molnár et al., 1995; Lefebvre et al., 2002a, 2012a), which may affect eel swimming efficiency and ability to migrate to spawning areas (Palstra et al., 2007; Sjöberg et al., 2009). Infected eels may also suffer high mortality rates under stressful environmental conditions, such as high water temperatures (Molnár et al.,1991; Molnár, 1993; Baruš and Prokeš, 1996). Since its first discovery in a wild-caught American eel from South Carolina in 1995 (Fries et al., 1996), A. crassus has spread to many areas along the Atlantic coastline of North America (Barse and Secor, 1999; Barse et al., 2001; Moser et al., 2001; Machut and Limburg, 2008; Aieta and Oliveira, 2009; Rockwell et al., 2009; Hein et al., 2014). Most studies have examined infection of the yellow and silver eel stages, but there is little information on the younger glass eel and elver stages. Glass eels undergo a series of developmental changes as they recruit from the ocean into coastal waterways (Tesch, 2003). The timing of infection of newly recruited American eels is poorly understood. Barse et al. (2001) reported no infection in American eel elvers from the Chesapeake Bay, but in the Hudson River Machut and Limburg (2008) found A. crassus parasites in American eels as small as 70 mm, and European glass eels are known to become infected both experimentally (e.g. De Charleroy et al., 1990; Nimeth et al., 2000) and naturally (Lefebvre et al., 2002b). Given the recent interest in transporting glass eels to restock depleted and extirpated habitats in the USA and Canada (Symonds, 2006; ICES, 2013), as well as the live transport of glass eels for aquaculture, there is a need to understand the stage(s) at which American eels become infected in the wild. The objectives of this study were to (i) quantify A. crassus infection in A. rostrata glass eels and elvers collected from the wild, (ii) determine the earliest developmental stage at which infection occurs, and (iii) determine whether infection in these young eels varies seasonally. Our study area was a tidal creek leading into the Cooper River, which is the only location in SC with a legal glass eel fishery. Material and methods Collection of eels Anguilla rostrata glass eels and elvers were collected from an eel ladder installed at the northeastern end of the Goose Creek Reservoir dam in North Charleston, SC (latitude +32.933140, longitude 280.008803). The eel ladder consists of a covered aluminium ramp with flowing water to allow eels to swim from below the dam to the top of the dam. Once at the top, eels fell into a catch basin filled with circulating reservoir water, where they remained until collected. Eel catches were enumerated from the basin on 127 occasions during January December 2013. On 54 of those occasions, from March through December only, a subsample of eels was kept and returned to the laboratory for parasite screening. Goose Creek Reservoir surface water temperature was recorded on each occasion and ranged from 48C in February to 348C in July (Figure 1). Goose Creek Reservoir is connected to the Cooper River via Goose Creek, which is 16.5 km long. Salinity at the head of the creek (i.e. at the base of the eel ladder, immediately below the dam) is typically near zero due to freshwater outflow from the reservoir, but during low-flow conditions may reach 5 ppt due to tidal influences. Salinity near the mouth of the creek (confluence with Cooper River) has been observed to range between 3 and 24 ppt, depending on tidal stage and water flow conditions (SCDNR Inshore Fisheries Section, unpubl. data). Screening for eel parasites In all, 473 glass eels and elvers were returned to the laboratory for screening (n.b. no yellow or silver eel stages were captured in the ladder). Eel total length (TL) was measured to the nearest millimetre. The glass eel pigment stage (1 7) was determined using Figure 1. South Carolina Goose Creek Reservoir surface water temperature (circles) plotted against day of the year during 2013. The black line is the maximum daily water temperature recorded in the Cooper River, which Goose Creek flows into (United States Geological Survey surface water site 021720677, accessed through http:// waterwatch.usgs.gov, November 2014).

16 J. L. Hein et al. the key of Haro and Krueger (1988), and fully pigmented eels were categorized as elvers. Glass eels (n ¼ 274) ranged from 34 to 91 mm TL with a mean (+SE) of 56.0 + 0.4 mm, and elvers (n ¼ 199) ranged from 62 to 156 mm TL with a mean of 94.1 + 1.1 mm (Figure 2, Table 1). In most months from March to December, both glass eels and elvers were screened. The exceptions were September and October, when only elvers were caught on the eel ladder. Eels were dissected and numbers of larval (L3 and L4 stages) and adult A. crassus parasites were determined by examining a swimbladder squash under a compound microscope (larvae) or by gross examination of the swimbladder lumen (adults) (Hein et al., 2014). Prevalence (percent of eels infected by A. crassus parasites), mean abundance (number of A. crassus parasites per eel examined), and mean intensity (number of A. crassus parasites per infected eel) (Bush et al., 1997) were calculated by the parasite stage (i.e. for just larval, or just adult A. crassus parasites) and also for overall infection (i.e. infection by any A. crassus stage). Figure 2. Size distribution of A. rostrata specimens that were subsampled during 2013 from the South Carolina Goose Creek Reservoir eel ladder and screened for infection by A. crassus parasites. Grey, glass eels; black, elvers. Statistical analyses A one-way ANOVA, with Tukey s pairwise post hoc tests, was used to test for differences in TL among eel development stages. Logistic regressions (logit-link) were used to test the effects of eel TL (covariate) and eel development stage and month (categorical factors) on the prevalence of parasite infection. Generalized linear models (Poisson distribution) were used to test the effects of the glass eel pigmentation stage on parasite abundance. Results The highest catch rates of eels (mean number per day) on the eel ladder occurred in January and February due to large numbers of glass eels moving up the eel ladder in those months. Catch rates declined to a minimum in August, and then increased modestly through December (Figure 3a). Glass eels were present from January through August, but were absent in September and October before reappearing in November and December (Figure 3a). From March through August, glass eels generally progressed from less developed (mostly stages 1 3) to more developed stages (mostly stages 6 7) (Figure 3b). Glass eels that were captured in November and December (after the September October hiatus) reverted to less developed stages because they belonged to the subsequent year class (i.e. distinct year class from those caught earlier in the year; Figure 3b). Elvers were captured throughout most of the year and comprised the majority of the catches from August on due to lower glass eel numbers in those months (Figure 3a). Elvers had a significantly greater TL than all the glass eel stages (p, 0.001). Among just glass eels, TL differed significantly between pigment stages. Post hoc tests indicated that stages 1 4 did not differ significantly from each other, after which significant increases in TL occurred (Table 1). Overall prevalence (+SE) of infection by A. crassus parasites (i.e. larval and adult stages combined) was 29.4 + 2.1%, mean abundance was 0.88 + 0.12 parasites per eel, and mean intensity was 2.98 + 0.34 parasites per infected eel. Among just glass eels, values were 8.0 + 1.6%, 0.12 + 0.03, and 1.46 + 0.16, respectively, and among just elvers values were 58.8 + 3.5%, 1.92 + 0.26, and 3.27 + 0.40, respectively (Table 1). No A. crassus parasites were observed in any glass eel pigment stages 1 3. In glass eel pigment stages 4 7, only adult stages of A. crassus were found, except for a single A. crassus larva (together with an adult) found in a stage 6 glass eel collected in July. Among elvers, 17.1% were infected with larval A. crassus parasites and Table 1. Prevalence (P), mean abundance (A), and mean intensity (I) of A. crassus parasites in A. rostrata glass eels and elvers collected at the South Carolina Goose Creek Reservoir eel ladder between March and December 2013. A. crassus L3/L4 larvae A. crassus adults A. crassus, any stage Eel stage Pigment stage n Mean TL (mm) P (%) A I P (%) A I P (%) A I Glass eel 1 23 54.0 0.0 0.00 0.0 0.00 0.0 0.00 2 36 53.1 0.0 0.00 0.0 0.00 0.0 0.00 3 37 53.9 0.0 0.00 0.0 0.00 0.0 0.00 4 40 53.0 0.0 0.00 5.0 0.05 1.00 5.0 0.05 1.00 5 51 56.8 0.0 0.00 7.8 0.12 1.50 7.8 0.12 1.50 6 67 60.1 1.5 0.01 1.00 14.9 0.25 1.70 14.9 0.27 1.80 7 20 58.3 0.0 0.00 30.0 0.30 1.00 30.0 0.30 1.00 Glass eel All (1 7) 274 56.0 0.4 0.00 1.00 8.0 0.11 1.41 8.0 0.12 1.46 Elver Complete 199 94.1 17.1 0.51 2.97 56.3 1.41 2.51 58.8 1.92 3.27 TOTAL All 473 72.1 7.4 0.22 2.91 28.3 0.66 2.33 29.4 0.88 2.98 Glass eel pigment stages follow Haro and Krueger (1988).

Infection of newly recruited American eels by Anguillicoloides crassus 17 Figure 3. (a) Monthly mean (+SE) number of A. rostrata caught per day in the South Carolina Goose Creek Reservoir eel ladder during 2013 (white bars:, screening for A. crassus parasites did not occur; grey bars, screening for A. crassus parasites did occur), and the proportion of A. rostrata that were glass eels (dash line with circles), as opposed to elvers. Note the log-transformation of the left vertical axis. (b) Monthly composition of glass eel pigmentation stages, showing progression of stages from March through August, a hiatus of glass eel catches in September and October, and the beginning of the next year class of glass eels in November and December. 56.3% were infected with adult A. crassus parasites. Parasite gravidity was not routinely screened, but gravid female A. crassus adult worms (determined by the presence of developed eggs) were nevertheless observed in the swimbladder lumen of some of the infected elvers. Overall prevalence of infection and abundance of A. crassus parasites increased significantly as development progressed from stage 1 glass eels to elvers (p, 0.001 for both prevalence and abundance; Table 1). Overall parasite prevalence varied significantly with eel TL (p, 0.001) and month (p ¼ 0.01), with a significant interaction between them (p ¼ 0.002). Based on pairwise comparisons from the logistic model, the monthly effects were groupedintotwomainperiods:marchthroughjulyandaugust through December. From March through July, overall prevalence increased significantly with eel TL (Figure 4a). From August through December, prevalence was generally lower and it was less dependent on eel TL (Figure 4b). Similar effects of TL and month were detected for infections by just adult A. crassus worms (TL, p, 0.001; month, p ¼ 0.02, TL month, p ¼ 0.005), whereas only TL was significant for infections by larval stages of the A. crassus parasite (positive TL slope, p ¼ 0.001; month, p ¼ 0.16, TL month, p ¼ 0.98). From the plots of eel TL against capture date (Figure 5), it was clear that the relationship between TL and overall prevalence of infection by A. crassus parasites, described above, was due to lower prevalence among glass eels compared with high prevalence among the larger elvers. Indeed, among just the elvers, overall Figure 4. Overall prevalence of infection by A. crassus parasites (i.e. infection by any stage of the parasite) in A. rostrata collected from the South Carolina Goose Creek Reservoir eel ladder during 2013. Eel TLs have been grouped into 10 mm bins for the periods (a) March through July (n ¼ 358) and (b) August through December (n ¼ 115). Black portion of bar, infected eels; white portion of bar, uninfected eels; no bar, no eels sampled. prevalence was not related to TL (p ¼ 0.71), although it did vary significantly with month (p, 0.001). Overall prevalence among elvers was higher from March to July (77.1%) compared with August to December (38.3%). Among just the glass eels, overall prevalence of infection increased with TL (p, 0.001) and varied with month (p, 0.001). Discussion Our study indicates that A. rostrata glass eels become infected by A. crassus parasites within months of recruiting from the ocean into estuaries, and that infection generally progresses with the eel development stage. We did not find A. crassus parasites in any of the early glass eel pigment stages (1 3), but they were detected in more developed pigment stages (4 7), and also in the elvers. The

18 J. L. Hein et al. Figure 5. Infection by A. crassus parasites in A. rostrata glass eels (a) and elvers (b) collected from the South Carolina Goose Creek Reservoir eel ladder from March December 2013. Black plus, uninfected; red circle, infected by A. crassus larval and/or adult stages. smallest infected specimen was a stage 4 glass eel with a TL of 48 mm. This compares with a minimum infected size of 70 mm in the Hudson River watershed (Machut and Limburg, 2008). Conversely, Barse et al. (2001) did not find A. crassus parasites in elvers from Chesapeake Bay, despite high prevalence among yellow eels in that region. Age was probably an important factor that influenced infection by A. crassus parasites among the eels we sampled, since it affects the potential duration of exposure to A. crassus infective stages harboured in the environment by intermediate and paratenic hosts. The combined size distribution of glass eels and elvers in our study suggests that we captured two or three age classes of A. rostrata at any given time during the year, which is similar to the multi-age composition reported for small eels moving upstream in the St Lawrence River drainage (Dutil et al., 1989). Glass eels are commercially harvested from the estuary we studied, which could spread A. crassus parasites to other regions if eels are transported alive. The sizes and pigment stages of commercially harvested glass eels are not reported by the fishery, but a previous survey using commercial fykenet gear next to our study site captured glass eels between 45 and 66 mm TL belonging to pigment stages 1 7 (mean TL ¼ 54.1 mm, n ¼ 6193 during 2000 2009; W. C. Post and A. P. Hazel, SCDNR, unpubl. data). Coupled with the data from our study, this indicates that a proportion of commercially harvested glass eels is likely infected by A. crassus parasites. It was notable that we only detected the adult stages of A. crassus in glass eels, with the single exception of a stage 6 glass eel collected in July that harboured both a larval and an adult stage. In elvers, however, both larval and adult stages of the parasite were found (prevalence was 17.1 and 56.3%, respectively; Table 1). Glass eels probably acquired A. crassus larvae downstream from our study site, but only migrated upstream after the parasite had developed into the adult stage. Ashworth and Kennedy (1999) suggested that development of A. crassus larvae is arrested when A. crassus adults are already present in the swimbladder lumen. This process may have been responsible for the higher prevalence of larval A. crassus in elvers compared with glass eels (Table 1), since elvers were also more likely to be infected by adult stages. In support of this, 26% of elvers that were infected by A. crassus adults also harboured A. crassus larvae, whereas only 6% of elvers without adults had larvae. Some of the A. crassus adults found in elvers were also gravid, suggesting that small eels play a role in transporting the parasite upstream into freshwater habitats. The first exposure of glass eels to A. crassus parasites in our study system probably occurred very soon after they entered estuarine habitats from coastal shelf waters, as also suggested by Van Banning and Haenen (1990) for A. anguilla glass eels in Europe. It seems unlikely that glass eels would have encountered infective stages before then because the parasite is probably absent, or extremely rare, in offshore coastal waters, and feeding rates of glass eels are much lower at that time (Tesch, 2003). Salinity regimes encountered by eels before we captured them may have influenced their parasite infection levels. Prevalence of infection by A. crassus parasites has been shown to decline (Lefebvre and Crivelli, 2012), and larval development of the parasite to be partially impaired (Kennedy and Fitch, 1990), as salinities increase from freshwater to seawater conditions. Contrary to this, a recent survey covering multiple locations in SC showed that the highest prevalence of A. crassus parasites in yellow eels occurred at a high-salinity (.30 ppt) location (Hein et al., 2014), and other studies have reported A. crassus parasites from hyperhaline conditions (Loukili and Belghyti, 2007; Rockwell et al., 2009). The glass eels and elvers in our study were captured in near freshwater conditions, but they would have travelled 16.5 km along a brackish creek from the main channel of the Cooper River, where salinities are much higher, to reach the eel ladder. It is possible that the salinity gradient along the creek influences parasite infection, and that temporal variation in freshwater run-off and associated salinities affect A. crassus prevalence from one year to the next. The earliest date of observed infection among glass eels was 19 March (one of the nine glass eels was infected by an adult A. crassus worm), which is about 4 months after the first glass eels of a cohort recruit to the estuary (based on our November sampling

Infection of newly recruited American eels by Anguillicoloides crassus 19 data; Figure 3). In the European eel, A. anguilla, it takes 50 80 d at 18 208C for A. crassus L3 larvae to develop into an adult stage, although development is slower at colder temperatures and delayed considerably below 108C (Haenen et al., 1996; Knopf et al., 1998). Winter water temperatures in Goose Creek Reservoir and Cooper River were between 10 and 188C preceding the earliest detected glass eel infection in March (Figure 1), so it is plausible that A. crassus L3 larvae could have developed into adults by spring if L3 vectors were eaten by glass eels during winter. The diet of elvers near our study area includes insects (mainly chironomids), ostracods, amphipods, and fish (McCord, 1977). Intermediate host species of A. crassus parasites have not been exhaustively studied in North America, although previously we have been able to experimentally infect a freshwater cyclopoid copepod from Goose Creek with A. crassus larvae (unpublished data). In Europe, a wide variety of intermediate and paratenic hosts have been identified, including copepods, ostracods, insects, snails, tadpoles, and fish (e.g. Hirose et al., 1976; Kim et al., 1989; Petter et al., 1989; Moravec and Konecny, 1994; Ooi et al., 1997; Moravec et al., 2005; review by Moravec, 2013), and this lack of specificity probably accounts for the parasite s ability to successfully invade new regions (Kennedy and Fitch, 1990). From March to July, prevalence of infection increased significantly with eel TL. Studies on the European eel, A. anguilla, have documented similar positive correlations between host size and infection by A. crassus parasites (Möller et al., 1991; Thomas and Ollevier, 1992; Molnár et al., 1994; Lefebvre et al., 2002b). This relationship occurs as eels grow and develop, likely because they consume more food and have a longer exposure to the parasite in the environment. Larger eels may also provide a larger habitat for the parasite to establish (Möller et al., 1991; Thomas and Ollevier, 1993; Molnár et al., 1994; Lefebvre et al., 2002b). In our study, the effect of eel TL was driven mostly by the difference between small glass eel stages (low prevalence in small, recently recruited eels) and larger elvers (high prevalence in larger, older eels). Prevalence among just the elvers was high from March to July (77.1%), and not related to TL. Although its effect was significant, length was a poor predictor of infection among just the glass eels because there was little variation in TL between pigment stages (Table 1). Such slow growth (or even regression in size) during glass eel development is likely due to the energetic costs they endure soon after recruiting to estuaries (Appelbaum et al., 1998; Tesch, 2003), but it is not known whether growth is further impacted by infection. From August to December, prevalence of infection by A. crassus parasites was lower than earlier in the year, and there was no relationship between prevalence and TL. A similar decline in infection by A. crassus parasites in late summer was observed in adult eels in SC (Hein et al. 2014) and, although not yet fully understood, it may have been driven by several causes. For example, in our study, infected eels may have cleared their infections (A. crassus adult stages die after reproducing), or the infected eels may have died. Information about mortality of glass eels and elvers infected by A. crassus parasites is lacking, but mortality of infected A. anguilla yellow eels during summer has been reported in Europe (Molnár et al., 1991; Baruš and Prokeš, 1996) and was attributed to a combination of extreme abiotic water conditions and pathological impacts of anguillicolosis. Molnár (1993) determined experimentally that mortality of infected eels occurred at dissolved oxygen levels less than 3 mg l 21 and water temperatures greater than 338C. Water temperatures during our study approached or exceeded this temperature threshold in summer (Figure 1). From August to December, it is likely that a portion of the elvers we examined belonged to the same year class as the young-of-the year glass eels caught earlier in the year, since glass eel pigment development was near complete by August (Figure 3b) and glass eels started to show evidence of growth from June on (Figure 5). This transition may have contributed towards the switch in dynamics of infection after July, since prevalence of infection was lower among young-of-the-year eels. In conclusion, we detected A. crassus parasites in A. rostrata elvers and late stage (4 7) glass eels, but not in early stage (1 3) glass eels. Further research is required to determine the mortality and health impacts of A. crassus infection on glass eels and elvers, since these younger eel stages may be more vulnerable than older eels. Infection by A. crassus parasites in very small, newly recruited glass eels, and the presence of the parasite s eggs within the swimbladder lumen of elvers indicate a high risk of spreading the parasite by moving young stages of live eels. This is particularly relevant with respect to our study area because it is one of the few locations in the USA where a glass eel fishery is currently permitted. Acknowledgements We thank SCDNR s Inshore Fisheries Section and Anadromous Section for field and laboratory support during the project. Funding was provided by the Atlantic Coast Fish Habitat Partnership, the Atlantic Coastal Fisheries Cooperative Management Act, and a South Carolina State Wildlife Grant (U.S. Fish and Wildlife Services). We are grateful to Professor David Secor and two anonymous reviewers for helping improve the manuscript. This is publication number 732 from the Marine Resources Division, South Carolina Department of Natural Resources. References Aieta, A. E., and Oliveira, K. 2009. Distribution, prevalence, and intensity of the swim bladder parasite Anguillicola crassus in New England and eastern Canada. Diseases of Aquatic Organisms, 84: 229 235. Appelbaum, S., Chernitsky, A., and Birkan, V. 1998. Growth observations on European (Anguilla anguilla L.) and American (Anguilla rostrata Le Sueur) glass eels. Bulletin Français de la Pêche et de la Pisciculture, 349: 187 193. Ashworth, S. T., and Kennedy, C. R. 1999. Density-dependent effects on Anguillicola crassus (Nematoda) within its European eel definitive host. Parasitology, 118: 289 296. ASMFC. 2012. American eel benchmark stock assessment. Stock Assessment Report 12 01. Atlantic States Marine Fisheries Commission, Washington, DC. Avise, J. C., Helfmant, G. S., Saunders, N. C., and Hales, L. S. 1986. Mitochondrial DNA differentiation in North Atlantic eels: population genetic consequences of an unusual life history pattern. Proceedings of the National Academy of Sciences of the USA, 83: 4350 4354. Barse, A. M., McGuire, S. A., Vinores, M. A., Eierman, L. E., and Weeder, J. A. 2001. The swimbladder nematode Anguillicola crassus in American eels (Anguilla rostrata) from middle and upper regions of Chesapeake Bay. Journal of Parasitology, 87: 1366 1370. Barse, A. M., and Secor, D. H. 1999. An exotic nematode parasite of the American eel. Fisheries, 24: 6 10. Baruš, V., and Prokeš, M. 1996. Length-weight relations of uninfected and infected eels (Anguilla anguilla) by Anguillicola crassus (Nematoda). Folia Zoologica, 45: 183 189. Boon, J. H., Cannaerts, V. M. H., Augustijn, H., Machiels, M. A. M., De Charleroy, D., and Ollevier, F. 1990. The effect of different infection levels with infective larvae of Anguillicola crassus on hematological parameters of the European eels (Anguilla anguilla). Aquaculture, 87: 243 253.

20 J. L. Hein et al. Bush, A. O., Lafferty, K. D., Lotz, J. M., and Shostak, A. W. 1997. Parasitology meets ecology on its own terms: Margolis et al. revisited. Journal of Parasitology, 83: 575 583. De Charleroy, D., Grisez, L., Thomas, K., Belpaire, C., and Ollevier, F. 1990. The life cycle of Anguillicola crassus. Diseases of Aquatic Organisms, 8: 77 84. Dutil, J-D., Michaud, M., and Giroux, A. 1989. Seasonal and diel patterns of stream invasion by American eels (Anguilla rostrata) in the northern Gulf of St. Lawrence. Canadian Journal of Zoology, 67: 182 188. Emde, S., Rueckert, S., Kochmann, J., Knopf, K., Sures, B., and Klimpel, S. 2014. Nematode eel parasite found inside acanthocephalan cysts a Trojan horse strategy? Parasites and Vectors, 7: 504. Fries, L. T., Williams, D. J., and Johnson, S. K. 1996. Occurrence of Anguillicola crassus, an exotic parasitic swimbladder nematode of eels, in the southeastern United States. Transactions of the American Fisheries Society, 125: 794 797. Haenen, O. L. M., Van Wijngaarden, T. A. M., Van der Heijden, M. H. T., Hoglund, J., Cornelissen, J. B. J. W., Van Lengoed, L. A. M. G., Borgsteede, F. H. M., et al. 1996. Effects of experimental infections with different doses of Anguillicola crassus (Nematoda, Dracunculoidea) on European eel (Anguilla anguilla). Aquaculture, 141: 41 57. Haro, A. J., and Krueger, W. H. 1988. Pigmentation, size, and migration of elvers (Anguilla rostrata (Lesueur) in a coastal Rhode Island stream. Canadian Journal of Zoology, 66: 2528 2533. Hein, J. L., Arnott, S. A., Roumillat, W. A., Allen, D. M., and de Buron, I. 2014. Invasive swimbladder parasite Anguillicoloides crassus: infection status 15 years after discovery in wild populations of American eel Anguilla rostrata. Diseases of Aquatic Organisms, 107: 199 209. Hirose, H., Sekino, T., and Egusa, S. 1976. Notes on the egg deposition, larval migration, and intermediate host of the nematode Anguillicola crassus in the swimbladder of eels. Fish Pathology, 11: 27 31. ICES. 2013. Report of the Joint EIFAAC/ICES Working Group on Eel (WGEEL), 18 22 March 2013 in Sukarietta, Spain, 4 10 September 2013 in Copenhagen, Denmark. ICES Document CM 2013/ACOM: 18. 851 pp. Kennedy, C. R., and Fitch, D. J. 1990. Colonization, larval survival, and epidemiology of the nematode Anguillicola crassus, parasitic in the eel, Anguilla anguilla, in Britain. Journal of Fish Biology, 36: 117 131. Kim, Y-G., Kim, E-B., Kim, J-Y., and Chun, S-K. 1989. Studies on a nematode, Anguillicola crassa parasitic in the air bladder of the eel. Journal of Fish Pathology, 2: 1 18. Knopf, K., Würtz, J., Sures, B., and Taraschewski, H. 1998. Impact of low water temperature on the development of Anguillicola crassus in the final host Anguilla anguilla. Diseases of Aquatic Organisms, 33: 143 149. Laetsch, R., Heitlinger, E. G., Taraschewski, H., Nadler, S. A., and Blaxter, M. L. 2012. The phylogenetics of Anguillicolidae (Nematoda: Anguillicoloidea), swimbladder parasites of eels. BMC Evolutionary Biology, 12: 60. Lefebvre, F., Contournet, P., and Crivelli, A. J. 2002a. The health state of the eel swimbladder as a measure of parasite pressure by Anguillicola crassus. Parasitology, 124: 457 463. Lefebvre, F., Contournet, P., Priour, F., Soulas, O., and Crivelli, A. J. 2002b. Spatial and temporal variation in Anguillicola crassus counts: results of a 4 year survey of eels in Mediterranean lagoons. Diseases of Aquatic Organisms, 50: 181 188. Lefebvre, F., and Crivelli, A. J. 2012. Salinity effects on anguillicolosis in Atlantic eels: a natural tool for disease control. Marine Ecology Progress Series, 471: 193 202. Lefebvre, F., Fazio, G., and Crivelli, J. 2012a. Anguillicoloides crassus. In Fish Parasites: Pathobiology and Protection, pp. 310 326. Ed. by P. T. K. Woo, and K. Buchmann. CABI, Wallingford, Oxfordshire, Cambridge, MA. 383 pp. Lefebvre, F., Wielgoss, S., Nagasawa, K., and Moravec, F. 2012b. On the origin of Anguillicoloides crassus, the invasive nematode of anguillid eels. Aquatic Invasions, 7: 443 453. Loukili, A., and Belghyti, D. 2007. The dynamics of the nematode Anguillicola crassus, Kuvahara 1974 in eel Anguilla anguilla (L. 1758) inthe Sebou estuary (Morocco). ParasitologyResearch, 100: 683 686. Machut, L. S., and Limburg, K. E. 2008. Anguillicola crassus infection in Anguilla rostrata from small tributaries of the Hudson river watershed, New York, USA. Diseases of Aquatic Organisms, 79: 37 45. McCord, J. W. 1977. Food habits and elver migration of American eel, Anguilla rostrata (LeSueur), in Cooper River, South Carolina. MS thesis, Clemson University, Clemson, SC. 47 pp. Möller, H., Holst, S., Lüchtenberg, H., and Petersen, F. 1991. Infection of eel Anguilla anguilla from the River Elbe estuary with two nematodes, Anguillicola crassus and Pseudoterranova decipiens. Diseases of Aquatic Organisms, 11: 193 199. Molnár, K. 1993. Effect of decreased oxygen content on eels (Anguilla anguilla) infected by Anguillicola crassus (Nematoda: Dracunculoidea). Acta Veterinaria Hungarica, 41: 349 360. Molnár, K., Székely, C., and Baska, F. 1991. Mass mortality of eel in Lake Balaton due to Anguillicola crassus infection. Bulletin of the European Association of Fish Pathologists, 11: 211 212. Molnár, K., Szakolczai, J., and Vetesi, F. 1995. Histological changes in the swimbladder wall of eels due to abnormal location of adults and second stage larvae of Anguillicola crassus. Acta Veterinaria Hungarica, 43: 125 137. Molnár, K., Székely, C., and Perenyi, M. 1994. Dynamics of Anguillicola crassus (Nematoda: Dracunculoidea) infection in eels of Lake Balaton, Hungary. Folia Parasitologica, 41: 193 202. Moravec, F. 2013. Parasitic Nematodes of Freshwater Fishes of Europe, 2nd edn. Academia, Praha. Moravec, F., and Konecny, R. 1994. Some new data on the intermediate and paratenic hosts of the nematode Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974 (Dracunculoidea) a swimbladder parasite of eels. Folia Parasitologica, 41: 65 70. Moravec, F., Nagasawa, K., and Miyakawa, M. 2005. First record of ostracods as natural intermediate hosts of Anguillicola crassus, a pathogenic swimbladder parasite of eels Anguilla spp. Diseases of Aquatic Organisms, 66: 171 173. Moser, M. L., Patrick, W. S., and Crutchfield, J. U., Jr. 2001. Infection of American eels, Anguilla rostrata, by an introduced nematode parasite, Anguillicola crassus, in North Carolina. Copeia, 3: 848 853. Nimeth, K., Zwerger, P., Würtz, J., Salvenmoser, W., and Pelster, B. 2000. Infection of the glass-eel swimbladder with the nematode Anguillicola crassus. Parasitology, 121: 75 83. Ooi, H. K., Lin, C. C., Chen, M. C., and Wang, W. S. 1997. Eucyclops euacanthus (Copepoda: Cyclopidae) is an intermediate host of Anguillicola crassus (Nematoda: Dracunculoidae) in Taiwan. Taiwan Journal of Veterinary Medicine and Animal Husbandry, 67: 135 138. Ooi, H. K., Wang, W. S., Chang, H. Y., Wu, C. H., Lin, C. C., and Hsieh, M. T. 1996. An epizootic of anguillicolosis in cultured American eels in Taiwan. Journal of Aquatic Animal Health, 8: 163 166. Palstra, A. P., Heppener, D. F. M., Van Gikkeken, V. J. T., Székely, C., and Van den Thillart, G. E. E. J. M. 2007. Swimming performance of silver eels is severely impaired by the swim-bladder parasite Anguillicola crassus. Journal of Experimental Marine Biology and Ecology, 352: 244 256. Petter, A. J., Fontaine, Y. A., and Le Belle, N. 1989. Etude du développement larvaire de Anguillicola crassus (Dracunculoidea, Nematoda) chez un Cyclopidae de la région parisienne. Annales de Parasitologie Humaine et Comparée, 64: 347 355. Rockwell, L. S., Jones, K. M. M., and Cone, D. K. 2009. First record of Anguillicoloides crassus (Nematoda) in American eels (Anguilla rostrata) in Canadian estuaries, Cape Breton, Nova Scotia. Journal of Parasitology, 95: 483 486. Sjöberg, N. B., Petersson, E., Wickström, H., and Hansson, S. 2009. Effects of the swimbladder parasite Anguillicola crassus on the

Infection of newly recruited American eels by Anguillicoloides crassus 21 migration of European silver eels Anguilla anguilla in the Baltic Sea. Journal of Fish Biology, 74: 2158 2170. Symonds, J. E. 2006. The American eel (Anguilla rostrata): stock enhancement review. Industrial Research Assistance Program, NRC and South Shore Trading Co Ltd. 135 pp. Székely, C., Palstra, A., Molnár, K., and Van den Thillart, G. 2009. Impact of the swim-bladder parasite on the health and performance of European eels. In Spawning Migration of the European Eel, pp. 199 224. Ed. by G. Van den Thillart, S. Dufour, and J. C. Rankin. Springer, London. 477 pp. Tesch, F W. 2003. The Eel, 3rd edn. Ed. by J. E. Thorpe. Blackwell Science, Oxford. 408 pp. Thomas, K., and Ollevier, F. 1992. Paratenic hosts of the swimbladder nematode Anguillicola crassus. Diseases of Aquatic Organisms, 13: 165 174. Thomas, K., and Ollevier, F. 1993. Hatching, survival, activity, and penetration efficiency of second stage larvae of Anguillicola crassus (Nematoda). Parasitology, 107: 211 217. Van Banning, P., and Haenen, O. L. M. 1990. Effect of the swimbladder nematode Anguillicola crassus in wild and farmed eel, Anguilla anguilla. In Pathology in Marine Science, pp. 317 330. Ed. by F. O. Perkins, and T. C. Cheng. Academic Press, New York. 538 pp. Vogel, G. 2010. Europe tries to save its eels. Science, 329: 505. Handling editor: David Secor