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Diseases of Aquatic Organisms

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DAO 129:41-51 (2018)  -  DOI:

Amyloodiniosis in cultured Dicentrarchus labrax: parasitological and molecular diagnosis, and an improved treatment protocol

Mohamed Bessat1,*, Amr Fadel2

1Department of Parasitology, Faculty of Veterinary Medicine, Alexandria University, Egypt
2Laboratory of Fish Diseases, National Institute of Oceanography and Fisheries (NIOF), Alexandria Branch, Egypt
*Corresponding author:

ABSTRACT: Amyloodinium ocellatum, the causative agent of amyloodiniosis (marine velvet, velvet disease), affects marine and brackish fish in various warm and temperate habitats. We recorded disease outbreaks with high morbidity and mortality rates in marine-cultured European seabass Dicentrarchus labrax fry at 2 locations in northwest Egypt. The sudden outbreak, high morbidity and mortality rates, and skin lesions with a velvety appearance in affected fish all indicated A. ocellatum infection. This was further confirmed by microscopic findings of the parasitic stage (trophonts) in skin and gill smears. While ecological factors including water temperature and salinity were all amenable to parasite establishment and propagation, mortality rates differed between the 2 farms, with rates of mortality well correlated with prevalence and intensity of A. ocellatum infections. Characterization by PCR targeting rDNA gene fragments and subsequent DNA sequencing and phylogenetic analysis further confirmed the molecular identity of the A. ocellatum isolate, which was genetically similar to isolates from other geographical locations. Finally, an improved treatment method using dual hyposalination and copper sulfate exposure to increase the efficiency and decrease the toxicity of copper sulfate was tested. The gradual reduction in water salinity coupled with copper sulfate treatment was more efficient at controlling the disease than only applying copper sulfate. To our knowledge, this is the first parasitological and molecular characterization of A. ocellatum in marine cultures in Egypt. The high molecular identity and close phylogenetic relationship further confirmed the monophyletic nature of A. ocellatum isolates.

KEY WORDS: European seabass · Dicentrarchus labrax · Amyloodiniosis · PCR · Phylogenetic analysis · Copper sulfate treatment

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Cite this article as: Bessat M, Fadel A (2018) Amyloodiniosis in cultured Dicentrarchus labrax: parasitological and molecular diagnosis, and an improved treatment protocol. Dis Aquat Org 129:41-51.

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