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INTRODUCTION
subsp. piscicida, is the disease responsible for higher mortalities (Zorrilla et al., 1999),
becoming the main limiting factor for sole production.
2. Photobacterium damselae subsp. piscicida
Photobacterium damselae subsp. piscicida, an obligate halophilic bacterium, is the
causal agent of psedotuberculosis (Kubota et al., 1970), because in chronic cases,
affected fish show prominent white tubercles in several internal organs. This disease
was first described in wild populations of white perch (Morone americanus) and
stripped bass (Morone saxatilis) in the United States (Snieszko et al., 1964). Currently
natural hosts of the pathogen include a wide variety of marine fish. This disease has
great economic impact in Japan, where affects mainly yellowtail (Seriola
quinqueradiata) cultures (Kusuda and Salati, 1993), in the United States and in the
European Mediterranean area, causing important losses in gilthead seabream (Sparus
aurata, L.) (Ceshia et al., 1991; Toranzo et al., 1991), stripped seabass (Hauwke et al.,
1987), seabass (Dicentrarchus labrax, L.) (Baudin-Laurencin et al., 1991; Balebona et
al., 1992) and, recently, in sole (Solea senegalensis, Kaup) (Zorrilla et al., 1999;
Magariños et al., 2003; Arijo et al., 2005).
External pathological signs of the pseudotuberculosis are usually inconspicuous,
surface lesions being usually absent in affected fish. Occasionally, diseased gilthead
seabream and seabass display abnormal skin pigmentation or slight haemorrhagic areas
in the head and gills and swelling of the abdominal cavity (Toranzo et al., 1991;
Balebona et al. 1992; Fouz et al., 2000).
Internally, diseased fish show haemorrhagic septicaemia and necrosis in the
majority of the organs, displaying the typical tubercles consisting in accumulation of
bacteria, necrotic phagocytes and granulomes. Moreover the necrosis and the existence
of granulomata in spleen, kidney and liver, where bacteria are visible in the sinusoids
and within the hepatic vessels, have been reported (Kubota et al., 1970; Wolke, 1975;
Tung et al., 1985; Hawke et al., 1987; Toranzo et al., 1991; Balebona et al., 1992; Noya et
al., 1995a).
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