MASS MORTALITIES ASSOCIATED WITH ISOPODA INFESTATION AS A RESULT OF UNCONTROLLED BIOSECURITY MEASURES IN LAKE QARUN, EGYPT  

Crustacean parasitic infestations are associated with high fish mortalities and economic losses in aquaculture. Conventional chemical treatments to control these infestations adversely affect fish and aquatic environment. Therefore, finding alternative control measures through vaccination or environment-friendly approaches is currently a global concern.

Lake Qarun is a closed lake covers an area of 235 km2, and stretches for 40 km from east to west (Fig. 1). Water in the lake was originally fresh but is currently salty and turbid.

The present study aims to investigate the main reason behind the appearance of unusual external parasite heavily infesting all fish species and causing mass fish mortalities in Lake Qarun, Fayoum province, Egypt during the summer season of 2015.

A total number of 300 fish of three fish species Tilapia zilli, Mugil cephalus and Solea vulgaris (100/ each species) were collected and transported alive to the Faculty of Veterinary Medicine, Mansoura University, Egypt for clinical, parasitological, and pathological examination. In addition, water samples were also collected for the physicochemical analysis and measuring the concentration of trace element in water.

Parasitological results revealed the existence of two different types of isopod species identified as Nerocila orbignyi and Renocila thresherorum heavily infesting the branchial cavity of all the collected fish (fig.2). The gills showed sever congestion, edema and deformity of the gill arch (data not shown).

Water analysis (table 1) revealed higher salinity levels that enabled the unusual acclimatization of the infesting parasites. In addition, total dissolved Fe, Cd, Cu and Pb were higher than the permissible limits.  Finally, after investigating the main reason behind the presence of such parasites in this closed Lake, we concluded that it was due to a breach in the biosecurity measures during the routine fry transfer to the lake.  

Currently, fishing in the lake is totally prohibited by the government and the lake is almost free of fish that has a huge economic loss on the aquaculture industry.

Some control measures are currently being adopted trying to solve that problem in such an important Lake. In addition, we are trying to find a suitable measure to control parasite through detecting its virulence gene to be used as tool for vaccination strategy to limit its spreading in other fish farms or other lakes in Egypt.