Molecular Detection of Aeromonas hydrophila as the Main Cause of Outbreak in Tilapia Farms in Egypt

Abstract

Submit Manuscript | http://medcraveonline.com J Aquac Mar Biol 2015, 2(5): 00045 which represent 51.2% of Egyptian production and 7.27% of global production. Bacterial diseases are considered the main and most dangerous type of diseases affecting the fish production as it represents 80 % of fish mortalities [3]. Fish mortalities have negative impact on fish farming. Fish farming is not only provide a source of cheap animal protein and a source of income but also it is a source of employment. Continuous losses due, to fish mortalities may make fish farms owners to stop or change the activity that causes loss of thousands of worker to their jobs. In Kafrelsheikh, the semi intensive tilapia culture is the only system used in earthen bonds, fish farms supplied with agricultural drain water, fish density in studied farms is four fish per cubic meter. The most common bacterial disease affecting fish is motile Aeromonas septicemia caused by Aeromonas hydrophila. It is defined as septicemic disease worldwide distributed affecting numerous species of freshwater and marine fishes. It is also considered as the most significant disease which occurs in cultured freshwater fish [4]. Congestion and haemorrhages on the abdominal wall and at the base of fins with scale erosion at different parts of the body were the marked clinical signs observed [5] who also recorded severe congestion of internal organs with accumulation of ascetic fluid in abdominal cavity and swollen kidney and spleen. In Egypt, motile Aeromonas septicemia has a potential economic hazard in which it causes severe losses in cultured freshwater fish including Oreochromis niloticus, common carp, Mugil cephalous and Mugil capeto [6]. Increasing water change, elevation of water column highs and stop feeding helped in decreasing the deleterious effect of the outbreak but not solve the problem completely. So the present work aimed for the isolation and identification of the causative agent responsible for this outbreak in four tilapia farms in Kafrelsheikh by molecular detection using PCR. Materials and Methods Study area Samples were taken from four fish farms suffered from mass mortalities in Kafrelsheikh governorate north of Egypt. First farm located in Baltim, second farm in Torombat seven and other two farms in Elhamol. Sample: Sixteen live Nile tilapias (Oreochromis niloticus) showing the clinical signs of septicemia were sampled, as four fish were taken from each farm. Each fish weight ranged between150-500 gm. Each fish was packed alive in a separate stile labeled plastic bag and transported to lab in ice pox. Clinical examination: The clinical examination was performed according to the method described by Conroy & Hermann [6]. Post mortem examination: The post mortem examination was performed according to the method described by Austin & Austin [7]. Isolation and identification of the causative agent: Under sterile conditions one tryptic soy broth (oxoid) tube was inoculated with a platinal lope from heart blood, liver and kidney tissues of fish and incubated at 37 ̊ C for 18 hrs. Rimler-Shotts media with novobiocin selective supplement (Oxoid) plates were streaked with a loopful of cultured broth then incubated at 37 ̊ C for 24 hrs.The growing colonies were further identified by PCR. Research Article Abstract An outbreak recorded in Tilapia farms in Kafrelsheikh governorate with high mortalities ranged between 30-70 % in the summer season of 2014. This study was conducted for isolation and identification of the causative agent responsible for mortalities in four fish farms. Twelve Aeromonas isolates were identified by PCR using Aeromonas species primer at the molecular weight of (953 bp) then all strains were also confirmed by PCR as Aeromonas hydrophila using Aeromonas hydrophila specific-16S rRNA gene primer at the molecular weight of (103 bp).