Identification of a Vibrio sp. pathogenic for incubation of eggs of the European eel (Anguilla anguilla) and attempts to the treatment

Summary Background: The global warming; the overfishing of the sexually mature adult fish (the spawners) and the offspring; the environmental pollution and parasites have significant impact on severe decline in the European eel (Anguilla anguilla) stock. Objectives: For restocking purposes, several research projects about the elaboration of captive breeding methods and hatchery technology of eel, have been initiated. The detection of piscine pathogens and the development of effective therapeutic and prevention strategies against their infections during the early life stages in fish (eggs, larvae, fry, and smolts) under controlled conditions are essential for successful work. Materials and Methods: The aim of the present study was to identify the patho gen(s), and to make proposal for the possible treatments against the infection of the developing eel embryos, that produced by the controlled reproduction process following hormone-induced sexual maturation of female European eel. The patho genic bacteria were isolated on different selective media. They were characterised by morphological –, microscopic examinations and with some biochemical tests. Their taxonomic status was verified by using the Biolog MicroStation ID system, and by amplification and sequencing of the 16S rDNA genome region. Then their antimicro bial sensitivity was checked by Kirby-Bauer disc diffusion method using 10 various antibiotics (ampicillin, chloramphenicol, cotrimoxazole, enrofloxacin, erythromycin, florfenicol, furazolidone, gentamicin, oxytetracykline, polymyxin-B). Results and Discussion: The phenotypic and genotypic microbiological assays detected the presence of only one dominant species; that was the Vibrio cyclitroph icus, a member of Vibrio splendidus clade. The pathogenicity of these bacteria to larvae of molluscs and shrimps has been already known. Their emergence in the closed experimental system may be the result of the artificial sea water prepared from contaminated sea salt. Based on the antibiogram of the isolated bacterium strain the use of chloramphenicol and a consequent formalin treatment of the water for general disinfection is suggested