Detection and localization of streptococcus agalactiae in the ovary of nile tilapia (Oreochromis Niloticus) broodstock and evaluation of egg disinfection efficacy | |
| Author | Pravilada Wigraiphat |
| Call Number | AIT Thesis no.AQ-24-02 |
| Subject(s) | Bacterial diseases in fishes Fishes--Diseases Tilapia |
| 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 | Streptococcus agalactiae is a significant pathogen in Nile tilapia (Oreochromis niloticus), causing serious mortality worldwide in aquaculture. The disease has a significant impact on the reproduction of Nile tilapia broodstock. Although there have been several studies on S. agalactiae in Nile tilapia, the precise location of S. agalactiae and its effect on the tilapia ovary are unclear. The aim of this study was to explore the localization of S. agalactiae in the ovary of infected female Nile tilapia broodstock and the detection of fertilized eggs in the infected population. Using both bacteriological and qPCR techniques, there were 7/12 (58.33%) tested positive for S. agalactiae. On the other hand, three were 15.00% of apparently healthy broodstock (n=20) tested positive in their fertilized eggs. All isolated S. agalactiae were serotype III. Histopathologically, Gram staining sections of their ovary revealed the presence of Gram-positive cocci located both intracellularly within the oocyte, vesicle, yolk droplets, and connective tissue membrane of the oocytes, while extracellular cocci were found in blood vessels among the ovary, liver, and spleen of infected broodstock. Disinfectants like potassium permanganate at a concentration of 30 ppm for 10 minutes, formaldehyde at 4000 ppm for 10 minutes, and povidone-iodine concentrations up to 7.5 ppm for 1 minutes, ranging between 7.5 - 100 ppm for 1 - 10 minutes were found to be effective in reducing viable S. agalactiae in in vitro trials. In summary, this study highlights that S. agalactiae can be found both intracellularly and extracellularly in the ovaries of infected tilapia broodstock and in the fertilized eggs collected from apparently healthy fish in the same population. The findings suggest possible vertical transmission of S. agalactiae, and the necessity of using specific pathogen free broodstock for seed production. This study also suggests potential disinfectants that efficiently decrease viable S. agalactiae for further use in tilapia hatcheries. |
| Year | 2024 |
| Type | Thesis |
| School | School of Environment, Resources, and Development |
| 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) | Ha, Thanh Dong |
| Examination Committee(s) | Salin, Krishna R.;Tsusaka, Takuji W. |
| Scholarship Donor(s) | Ministry of Agriculture and Cooperatives (MOAC), Thailand;AIT Scholarships |
| Degree | Thesis (M. Sc.) - Asian Institute of Technology, 2024 |