Abstract
Background:
Vibrios are aquatic bacteria and ubiquitous in the marine environment causing Vibriosis in humans and aquatic animals. Vibriosis is a significant disease of cultured and wild fish living in marine water, brackish, and freshwater, which causes highly economic losses.
Aim:
The present study was aimed to address the impact of Vibrios on the health status of Trachurus trachurus inhabiting coastal area of Tripoli.
Methods:
A total of 100 samples of (Trachurus trachurus) were collected randomly from the Western Coast of Tripoli and Bab Al- Baher market, throughout the period from spring 2019 to summer 2019.All the sampled fish were examined externally and internally to identify any potential lesions. Bacterial isolation from liver and kidney was carried out using the appropriate culture media. Tissue samples were taken from liver, kidney and spleen in 10% neutral buffered formalin for histopathology examination. The tissue sections were stained with Hematoxylin and Eosin (H&E) to assess morphologically and Perl's Prussian blue for the demonstration of ferric iron.
Results:
On average 69% of the infected fish exhibited at least one pathological lesion. Vibrios were recovered from 90% of the examined fishes. The histopathological changes in the liver were observed as severe congestion of blood vessels, mononuclear cell infiltration surrounding a bile duct, granular degeneration and coagulative necrosis of hepatocytes in the centrilobular area, marked vacuolar degeneration of hepatocytes, activation of melano-macrophages centers (MMCs), multiple cysts of nematode in hepatic tissue (incidental finding). With respect to kidney and spleen, examination of H & E stained tissue sections have severe congestion of blood vessels, vacuolar degeneration of the renal tubular epithelium, severe interstitial mononuclear cell infiltration, and marked activation of melano-macrophages centers (MMCs) in the kidney. Moreover, congestion of blood vessels and marked activation of melano-macrophages (MMCs) were found in the spleen. The melano-macrophage centers (MMCs) of most of the sampled tissues showed a strong positive reaction for ferric iron.
Conclusion:
The polluted aquatic environment by sewage at Tripoli Coast is an essential factor for triggering the pathogenicity and invasion of Vibrios to vulnerable Atlantic horse mackerel fishes. Also, this study are a preliminary step to give a baseline for further future studies on epidemiology and control of Vibrio infection in Libyan fish.

Key words: Atlantic horse mackerel fish, Vibrionaceae, Histopathological changes, Melano-macrophages centers