The Department of Microbiology, Parasitology, and Biotechnology is pleased to announce to the scientific community and extend its heartfelt congratulations to Dr. Edward Samwel Mayila (first from the left in the picture) on the successful defense of his PhD on 4th February 2025 at the Department of Biology, Faculty of Sciences and Bioengineering Sciences, Vrije Universiteit Brussel (VUB) under the Ecology, Evolution and Genetics research group.
Dr. Mayila has been an academic member of staff at Sokoine University of Agriculture since 2016, serving in the Department of Microbiology, Parasitology, and Biotechnology, College of Veterinary Medicine and Biomedical Sciences.
His PhD thesis, titled “Environmental Trace Metal Status and Their Effects on Sharptooth Catfish (Clarias gariepinus) Immune Cell Population and Functioning in Tanzania,” explores the impact of trace metals on fish immunity in aquatic ecosystems.
Dr. Mayila began his PhD studies at VUB in October 2021, pursuing a Doctor of Philosophy in Sciences. He was supervised by Prof. Dr. Marc Kochzius (Vrije Universiteit Brussel), Dr. Cyrus Rumisha (Sokoine University of Agriculture, TZ), and Dr. Alexander Mzula (Sokoine University of Agriculture, TZ).
Once again, congratulations to Dr. Edward Samwel Mayila on this outstanding achievement!
Panel Members for the PhD Defense
| Name | Role | |
| 1 | Prof. dr. Luc Leyns (VUB, chair) | Chair |
| 2 | Prof. dr. Wen-Juan Ma (VUB) | Secretary |
| 3 | Prof. dr. Martine Leermakers (VUB) | Examiner |
| 4 | Prof. dr. Gudrun De Boeck (UAntwerpen) | Examiner |
| 5 | Prof. dr. Lieven Bervoets (UAntwerpen) | Examiner |
Summary of findings
Trace metals are naturally occurring elements, which can negatively affect biota at low concentrations due to their persistence and bioaccumulation in the food chain. This study assessed the environmental pollution status of eleven trace metals (Al, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, V, Zn) and arsenic using ICP-MS. This study also assessed the immune status of catfish by analyzing blood cells (WBC, RBC, Hb) and microflora. Samples were collected from the upper and lower Ruvu, Rufiji, and Matandu Rivers and a pond near Java-Saadani, in Tanzania. An experimental exposure study with Cd stress on the blood cell population and functioning was also conducted.
The results showed low to moderate pollution levels, with nickel posing the least ecological risk. Trace metal concentrations in catfish tissues were within WHO/FAO/EU limits. The Target Hazard Quotient (THQ) and Hazard Index (HI) were <1, indicating low risk. Trace metal concentrations in catfish tissues were within WHO, FAO, and EU limits. The Target Hazard Quotient (THQ), Hazard Index (HI), and carcinogenic risk were low, indicating minimal risk to the biota.
In-vivo blood parameters varied by site, with lower Ruvu showing the highest values: WBC (37.32 × 10³ cells/µl), RBC (1.4 × 10⁶ cells/µl), Hb (6.04 g/dl). Microflora load was highest at lower Ruvu (405 × 10⁸ CFU/ml).
Experimental cadmium exposure reduced WBC and RBC counts, increased cell fragility, and impaired phagocytosis. WBC counts in control tanks remained stable (28.8 to 32.0 × 10³ cells/µl), but in the treatment group, they progressively decreased (18.7 to 32.0 × 10³ cells/µl in week 1, 13.5 to 29.8 × 10³ cells/µl in week 2, 9.6 to 28.8 × 10³ cells/µl in week 3). RBC counts declined from 1.9 × 10⁶ cells/µl in week 1 to 1.2 × 10⁶ cells/µl in week 3, while Hb dropped from 9.3 g/dl to 5.0 g/dl.
Continued monitoring of trace metals is recommended to detect early pollution signs.
Publications:
- https://doi.org/10.1371/journal. pone.0306335.
- Edward S. Mayila, Alexanda Mzula, Cyrus Rumisha, Marc Kochzius 2025. Effects of Cd exposure on peripheral blood cell population and functional changes in innate immunity of the African sharptooth catfish (Clarias gariepinus), Comparative Immunology Reports, Volume 8, 200191. FULL TEXT
- https://bmcresnotes.biomedcentral.com/articles/10.1 186/s13104-016-2283-0