Histopathological Examination of Wild American Eels Infected with Anguillicola crassus (original) (raw)
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Journal of Fish Diseases, 2011
This study compares two alternative indices for quantifying the gross pathology of the swimbladder of eels, Anguilla anguilla (L.), infected with the nematode Anguillicoloides crassus. Two observers recorded twice the scores obtained by the two indices on the same set of 71 wild caught eels (from elver to silver eels, French Mediterranean lagoons). The Length Ratio Index (LRI), performed better than the Swimbladder Degenerative Index (SDI), in three of four predefined criteria of decision. First, the LRI better correlated with an estimate of the swimbladder volume reduction, a functional consequence of the infection (representativeness). Also, the LRI was less prone to subjectivity (inter-observer variability) and more precise (intra-observer variability), although less easy to generate (time needed for measurement/ assessment). Using a sub-sample of 32 unaffected eels (showing minor if any swimbladder damage and no living worms at autopsy), we ascertained a linear relationship between the swimbladder length and the total body length, a prerequisite of isometric growth, to definitively accept the new ratio index as a valid alternative to the SDI. Also, because the LRI can be recorded on live specimens with radio-imagery (non-invasive method), we recommend its use, and provide a graph of correspondence between the SDI scores, the LRI scores and the estimated proportion of gas loss in the swimbladder.
Aquaculture, 1996
To study the effects of various doses of Anguilficolu crassus in primary infections, parasite-free European eels were orally infected with doses of 0, 1, 5, 10, 20 or 40 third-stage (L3) larvae. The eels were either killed and examined for parasites and lesions after 56 days, or reinfected with 20 L3 larvae to study the effect of primary infection on resistance. Reinfected eels were killed and examined on Day 112. Blood samples were collected weekly and examined in an enzyme-linked immunosorbent assay (ELISA) to detect antibodies against adult parasite cuticula antigen. The mean percentage of A. CMSSUS recovered from eel swimbladders ranged from 14 to 20% on Day 56 and from 9 to 26% on Day 112. There was no significant relation between the proportion of recovered parasites and the primary and/or secondary infection dose. Furthermore, the higher the dose, the more severe were the haemorrhages and pigment spots seen in the swimbladder. Reinfected eels had significantly more severely thickened swimbladders, haemorrhages in the swimbladders and congestion of blood vessels in the swimbladders. Results of the ELISA showed that the eels developed no detectable antibody response against A. crassus. We concluded that under the given stressful experimental conditions, although eels develop pathological signs after 0044-8486/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDl 0044.8486(95)0 12 13-3 42 O.L.M. Haenen et d./Aquaculture 141 (1996) 41-57 primary and secondary infection with A. craws, they do not develop an antibody response or resistance.
Diseases of Aquatic Organisms, 1989
Migration pattern of third-stage Anguillicola crassus larvae, and pathogenesis of the lesions induced by third-stage larvae, was investigated in European eel Anguilla anguilla L. Young elvers (l g) were fed infected Paracyclops fimbriatus (Copepoda). Eel samples were collected and examined histologically at varying intervals during the 6 mo post-infection period. Third-stage larvae (L-111) migrated directly through the intestinal wall and body cavity to the swimbladder within 17 h postinfection. L-IV larvae were detected 3 mo post-infection, and immature adults were detected within 4 mo post-infection. The parasites occasionally showed aberrant migration paths. Pathological effects caused by the parasite were less severe after experimentally induced infections than those detected in some natural infections.
Diseases of Aquatic Organisms, 2014
A year-round survey of American eels Anguilla rostrata was performed at 5 localities in South Carolina (SC), USA, 15 yr after the first infection by the nematode Anguillicoloides crassus was reported from Winyah Bay, SC. Infections by adult stages of A. crassus in the swimbladder lumen occurred with a prevalence of 45% (n = 479), a mean intensity (± SE) of 2.3 ± 0.2 worms per infected eel (range = 1−22), and a mean abundance of 2.0 ± 0.1 among all eels. Infections by larval stages of A. crassus in the swimbladder wall occurred with a prevalence, intensity, and abundance of 29%, 2.4 ± 0.3 (range = 1−15), and 0.7 ± 0.1, respectively (n = 471). Overall prevalence of the parasite (any stage) was 58%, with a mean intensity ± SE of 3.0 ± 0.2 and a mean abundance of 1.8 ± 0.2. Biomass of the adult parasite stage varied significantly with eel body length, but the direction of the effect depended on salinity. Prevalence and intensity of infection by adult nematodes varied by locality but not by eel total length, salinity, or season. Larval prevalence was significantly greater in the winter and spring and also differed among localities. The lack of seasonal effects on infection by the adult worm stage contrasts with studies from higher latitudes in North America and Europe and may be due to the warmer winter temperatures at southern latitudes. Significant variation in infection among localities reflects possible differences in abundance of intermediate and/or paratenic hosts. Overall, infection levels were higher than previous reports for eels in SC but comparable to more recent reports from other areas in North America.
Zoological …, 2008
Anguillicola crassus (Kuwahara, Niimi and Itagaki 1974) is an endemic swimbladder parasite of the Japanese eel Anguilla japonica in East Asia (Kuwahara et al. 1974, Nagasawa et al. 1994). Eels are infected by ingestion of 3rd-stage juveniles (L3 larvae) present in copepods, a crustacean that serves as an intermediate host (Kennedy and Fitch 1990, Ooi et al. 1997), or by preying on small paratenic fish hosts containing L3 larvae (Kirk 2003). Adult male and female nematodes copulate in the lumen of the eel's swimbladder.
Infection by Anguillicoloides crassus in a riverine stock of European eel, Anguilla anguilla
Fisheries Management and Ecology, 2010
Infection by the parasitic nematode Anguillicoloides crassus Kuwahara, Niimi & Itagaki, in a wild riverine stock of European eel, Anguilla anguilla (L.), in a near pristine river was investigated. Samples were collected on a seasonal basis in distinct habitats along the river gradient. This study highlighted the presence of the parasite and completion of the whole life cycle in eels from the Rı´o Esva. Infection levels by A. crassus were high at three sites between the mid river to the estuary and also varied among seasons. Condition of eels was lower at upstream sites compared with downstream locations. Although high-quality, environmental conditions in the Rı´o Esva may buffer the effects of A. crassus on eels, potential impacts and limiting factors for the parasite are discussed.