Abstract
Background:
Oreochromis aureus is a member of the tilapia family that is considered one of the main food sources in different countries all over the world.

Aim:
Thus, studying the different pathogens infecting tilapia species is still one of the interesting search points.

Methods:
One hundred and eighty specimens of O. aureus were collected from Lake Manzala and transported directly in iceboxes to the laboratory of the faculty of Science at Port Said University. The fish were categorized into two groups depending on their sex. 0.1 gram of muscles and the internal organs were examined. Statistical epidemiological parameters were used based on the sex of the fish. The histological changes of the most infected organs of each syndrome were detected.

Results:
Diplopstomiasis was more prevalent in females than in males. On the contrary, acanthamoebiasis was more abundant in males than females. Muscles and the liver were the most infected organs in diplopstomiasis and acanthamoebiasis, respectively. Muscles suffered from severe deformations in the bundles, while there were many granulomatous areas in the liver and there were inflammatory immune cellular infiltrations in both tissues.

Conclusion:
Besides diplopstomiasis, acanthamoebiasis was observed in all examined organs of the study samples, with different distributions and severity in these organs. Further investigations were recommended for more understanding of these pathological syndromes and their relationship to their host.

Key words: Diplopstomiasis, acanthamoebiasis, severity, distribution, histopathology