Helminth, protozoan and viral infections of the European eel, Anguilla anguilla

Ab Aziz, R

Abstract

The European eel, Anguilla anguilla, is an important catadromous fish that has been
classified as critically endangered due to severe population decline. The reasons for this are
not fully understood; however, infectious disease undoubtedly makes a contribution. To explore
this further, a total of 509 A. anguilla were sampled between 2008 and 2010 from 27 locations
across England and Wales. Following dissection, the swimbladder nematode Anguillicoloides
crassus was found present in 245 specimens sampled from 20 locations (48.1%). Significant
correlation was found between eel length and intensity of infection. However, no significant
correlation between eel condition factor and A. crassus infection was found. To explore the A.
crassus population further, microsatellite analysis of 7 loci from 72 nematodes, sampled from 10
different locations, was conducted. Although multiple alleles (between 12 and 38) existed at all
analysed loci, genetic differentiation of A. crassus was low (average FST = 0.037). Further
analyses (STRUCTURE, BAPS and UPGMA phylogeny) showed the existence of two distinct A.
crassus populations; one originating from the river Piddle and the other represented by the
remaining sites.
To examine eel for infection with the protozoan haemoflagellate Trypanosoma
granulosum, a nested PCR assay was developed to amplify a region of the parasite 18S rRNA
gene from heart tissue. Giemsa staining of eel blood sampled from specimens obtained the
river Gowy confirmed the robustness of the molecular diagnostic test. Overall, T. granulosum
was found to be highly prevalent (87.2%) in UK eel.
A PCR-based assay for detection of the Herpesvirus anguillae (HVA) DMA polymerase
gene was also developed. Heart screening revealed that H. anguillae was present in 176 eel
sampled from 26 locations (34.5%). Tissue-based screening of river Gowy eel showed that
HVA detection was tissue dependent. Morphological examinations showed that some eel
presented clinical signs of HVA infection, though most did not, suggesting that the virus is
primarily latent.
Overall, the prevalence of triple co-infections (A. crassus, T. granulosum and H.
anguillae), varied significantly according to sampling location; however, there was no
association between these infectious agents.

Citation

Ab Aziz, R. Helminth, protozoan and viral infections of the European eel, Anguilla anguilla. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Aug 5, 2021
• Award Date: Jul 1, 2012