Prevalence of Anguillicoloides crassus and growth variation in migrant yellow-phase American eels of the upper Potomac River drainage

Abstract

Prevalence of the non-native swim bladder nematode Anguillicoloides crassus has recently increased in American eels from estuaries of the North American Atlantic coast, but little is known about parasite prevalence or conditions of previous infection in upstream migrant eels within upper watersheds. This study is the first to confirm presence of A. crassus in the upper Potomac River watershed. We estimated A. crassus prevalence during 3 time periods: September to October 2006 (5/143 eels, 3.5%), August to October 2007 (0/49 eels), and June 2008 (0/50 eels). All eels were sampled from the Millville Dam eel ladder on the lower Shenandoah River, a Potomac River tributary located approximately 285 km upstream of Chesapeake Bay, USA. Of the 5 infected eels, parasite intensity was 1 for each eel, and mean intensity was also 1.0. A swim bladder degenerative index (SDI) was calculated for the 50 eels from the final sampling period, and 38% of those eels (19 of 50) showed signs of previous infection by A. crassus. We also aged 42 of the 50 eels (mean ± SE = 6.7 ± 0.29 yr, range 4 to 11 yr) from the final sampling period. Based on the range of possible SDI scores (0 to 6), severity of previously infected swim bladders was moderate (SDI = 1 or 2). Previously infected eels, however, had a lower length-at-age than that of uninfected eels. Female yellow-phase eels in upper watersheds develop into large highly fecund silver-phase adults; hence, a parasite-induced effect on growth of yellow-phase eels could ultimately reduce reproductive potential.

Influence of introduced vs. native parasites on the body condition of migrant silver eels

“…But this criterion is not the best reflecting the eel pathogenicity due to the short life cycle of A. crassus , and severely damaged swimbladders are shown to harbor very few or even no living nematodes [42, 63]. Nevertheless, using the Swimbladder Degenerative Index, Lefebvre et al [44] recently demonstrated that the most affected eels had greater body length and mass (+11% and +41% respectively) than unaffected eels of the same age.…”

Effects of the invasive swim bladder parasiteAnguillicola crassuson health and condition indicators in the European eel

“…Arguably, the migrating stage is the most important stage to study from a population viability perspective, rather than the body condition of earlier life stages. However, a study of American eel ( Anguilla rostrata ) found that eels with signs of previous infections with A. crassus (damage to the swim bladder) were shorter at a given age compared to eels that did not show any signs of previous infections (no damage to the swim bladder) (Zimmerman & Welsh, 2012). It is important to mention that our results showing no major observed effects of A. crassus concern only selected health indicators.…”

Effects of Infectious Diseases on Population Dynamics of Marine Organisms in Chesapeake Bay

“…Furthermore, Atlantic sturgeon (Acipenser oxyrinchus) with skin and gill infections of the trematode, Nitzschia sturionis, lost weight compared to uninfected Atlantic sturgeon (Matsche et al 2010). Similarly, American eel (Anguilla rostrata) infected with the swim bladder nematode, Anguillicoloides crassus, had a lower length-at-age than uninfected eels (Zimmerman and Welsh 2012). Dermo disease in the eastern oyster can slow growth and cause a reduction in condition index of the oysters (Paynter and Burreson 1991).…”

“…However, the upper watershed may be an important juvenile habitat for female American eels (Goodwin and Angermeier 2003). Therefore, an effect of A. crassus on growth could result in lower reproductive potential because American eels are semelparous with only one opportunity to spawn and smaller American eels would likely have lower fecundity (Zimmerman and Welsh 2012;Jessop 2018). During 2004During -2008 of Atlantic sturgeon from the Chesapeake Bay had infections of N. sturionis, which caused reduced growth (Matsche et al 2010).…”