Retrospective identification and pathogenicity of Aeromonas dhakensis in Nile tilapia, Oreochromis niloticus | |
| Author | Rajendran, Rahul |
| Call Number | AIT Thesis no.AQ-21-02 |
| Subject(s) | Fishes--Diseases Nile tilapia Microbiology |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Aquaculture and Aquatic Resources Management |
| Publisher | Asian Institute of Technology |
| Abstract | Motile aeromonads septicemia is a disease of great concern to the freshwater aquaculture industry, including Nile tilapia, one of the most farmed fish globally. The disease is caused by a group of motile Aeromonas spp. of which A. hydrophila was commonly documented to be the primary causative agent. In contrast, some other species of the same genus were commonly misidentified as A. hydrophila, but not correctly recognized as the causative species. This study focuses on a collection of Aeromonas spp. isolates that were previously isolated from diseased tilapia but were initially misidentified as A. hydrophila. These isolated strains were re-identified by using a combination of phenotypic tests, sequencing four housekeeping genes 16S rRNA, rpoB, rpoD and gyrB and multilocus sequence analysis (MLSA). These strains were identified as A. hydrophila (n=1) and A. dhakensis (n=4). Upon identification, the pathogenicity of these strains was tested by a challenge study on Nile tilapia juveniles. The fish was intraperitoneally injected with three doses of bacteria ≅105, 106 and 107 CFU/ml for 14 days. The mortality rate for A. dhakensis was 10-100% upon challenge doses compared to 30-90% for A. hydrophila. The clinical signs and histopathology of diseased fish were similar between the two species, with haemorrhages on the body, scale loss, body discoloration, fin rot etc. The histopathological signs include congestions and haemorrhages on the brain, kidney and liver. In summary, this study identified A. dhakensis as one of the motile Aeromonas species causing disease in tilapia and proved its pathogenicity in controlled laboratory challenge, adding to the growing list of bacterial pathogens that require more attention on surveillance and monitoring. |
| Year | 2021 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Salin, Krishna R. |
| Examination Committee(s) | Yakupitiyage, Amararatne;Loc Thai Nguyen |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship |
| Degree | Thesis (M. Sc.) - Asian Institute of Technology, 2021 |