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

Abstract

Keywords: Benedenia sp., biased sinusoidal field gelelectrophoresis, Caligus longipedis, ectoparasites,Lactococcus garvieae, striped jack.Infectious diseases have become more serious inaquaculture with the rapid development of intensiveculture systems and the increase in fish and shellfishspecies cultured. Transmission of pathogenic micro-organisms to fish is mainly because of horizontalmechanisms. Among co-habiting fish, direct trans-mission of pathogens through the water is the mostimportant, especially when macroscopic and micro-scopic injuries occur on fish body surfaces, becom-ing potential portals of entry for bacterial pathogens(Kanno, Nakai & Muroga 1989; Amaro, Biosca,Fouz, Alcaide & Esteve 1995). Injuries on the skinand gills of fish are frequently caused by ectopar-asites, such as copepods and monogeneans, feedingon host mucus, tissue and blood (Cusack & Cone1986; Nylund, Bjorknes & Wallace 1991; Nylund,Wallace & Hovland 1993). By these feedingactivities, ectoparasites become effective mechanicalvectors, potentially transferring pathogens frominfected to non-infected fish (Ahne 1985; Cusack& Cone 1986; Donoghue 1986; Cusack, Rand C Nylund et al. 1991; Xu, Shoemaker K Bandilla, Valtonen, Suom-alainen, Aphalo & Hakalahti 2006; Pylkko, Soum-alainen, Tiirola & Valtonen 2006; Xu et al. 2007),but none of these studies showed a clear similaridentity between pathogens in both ectoparasitesand fish.The present study was designed to determine ifectoparasites carry the same pathogen as that ofdiseased fish. We targeted Lactococcus garvieae, oneof the major Gram-positive cocci pathogenic forfish as well as animals and humans (Wang, Shie,Chen, Huang, Hsieh, Wen, Lin & Wu 2007). InJapan, L. garvieae infection has caused severemortalities to cultured fish belonging to the familyCarangidae, such as the yellowtail, Seriola quinqu-eradiata Temminck & Schlegel, greater amberjack,Seriola dumerili (Risso), yellowtail amberjack, Seri-ola lalandi Valenciennes, and striped jack, Pseudo-caranx dentex Bloch & Schneider, since 1974 (Kitao1982; Kusuda, Kawai, Salati, Banner & Fryer 1991;Eldar, Ghittino, Asanta, Bozzeta, Goria, Prearo &Bercovier 1996). We used biased sinusoidal field gelelectrophoresis (BSFGE) to differentiate L. garvieaeisolates from different origins.During August 2006, two diseased striped jack of27–28 cm standard length were collected from afish farm and examined at the Fish Disease Control