Homogeneity among Lactococcus garvieae isolates from striped jack, Pseudocaranx dentex (Bloch '' Schneider), and its ectoparasites

摘要

Infectious diseases have become more serious in aquaculture with the rapid development of intensive culture systems and the increase in fish and shellfish species cultured. Transmission of pathogenic microorganisms to fish is mainly because of horizontal mechanisms. Among co-habiting fish, direct transmission of pathogens through the water is the most important, especially when macroscopic and microscopic injuries occur on fish body surfaces, becoming potential portals of entry for bacterial pathogens (Kanno, Nakai & Muroga 1989; Amaro, Biosca, Fouz, Alcaide & Esteve 1995). Injuries on the skin and gills of fish are frequently caused by ectoparasites, such as copepods and monogeneans, feeding on host mucus, tissue and blood (Cusack & Cone 1986; Nylund, Bj?rknes & Wallace 1991; Nylund, Wallace & Hovland 1993). By these feeding activities, ectoparasites become effective mechanical vectors, potentially transferring pathogens from infected to non-infected fish (Ahne 1985; Cusack & Cone 1986; Donoghue 1986; Cusack, Rand & Cone 1988; Nylund et al. 1991; Xu, Shoemaker & Klesius 2007). However, there is little firm evidence to verify the role of ectoparasites as vectors. Bacterial and viral pathogens have been isolated from ectoparasites on infected fish (Mulcahy, Klaybor & Batts 1990; Bandilla, Valtonen, Suomalainen, Aphalo & Hakalahti 2006; Pylkko, Soumalainen, Tiirola & Valtonen 2006; Xu et al. 2007), but none of these studies showed a clear similar identity between pathogens in both ectoparasites and fish.