Systemic infection by Vibrio harveyi in humphead wrasse Cheilinus undulatus (Rüppell, 1835) at a public aquarium

The humphead wrasse, Cheilinus undulatus, also known as Napoleon wrasse or Maori, is one of the giant coral reef fish of the Indo-Pacific Area. In public aquaria C. undulatus is frequently exhibited for its huge body size, longevity and as a conservation ambassador of reef ecosystems. The knowledge about diseases of this precious and rare fish species is very limited and only a few disorders have been reported in literature. In May 2008 one humphead wrasse was introduced to the Cattolica Aquarium, Italy and exhibited in a 56,000 l tank together with a mixed population of teleosts, sharks and rays. In February 2017 the fish, weighing 15 kg, died and no clinical signs were observed in the days before its death. The fish was immediately necropsied and standard parasitological, bacteriological and histological exams were carried out in order to investigate causes of death. At necropsy, fish showed slightly pale gill and the presence of a severe fibrinous peritonitis. In the posterior part of the kidney, a diffuse area of necrosis with suppurative-like aspect was also observed. No gross lesions were noticed in other organs and no parasites have been found both macro and microscopically. After 24 h of incubation at 25±1°C, from all the inoculated organs (kidney, spleen, liver and brain) a number of morphologically similar colonies grew on TSA+1.5% NaCl and TCBS plates respectively. The isolates were identified as Vibrio harveyi and antibiotic sensitivity test was performed by Kirby-Bauer disk diffusion method. Histological exams showed the presence of bacterial aggregatesassociated to necrosis in most of the internal organs, especially in the kidney. Macrovacuolar liver steatosis was also observed. Furthermore several elongated fungal hyphae were found only in liver blood vessels. This case is to our knowledge the first report of systemic infection by Vibrio harveyi in a humphead wrasse and highlights the potential pathogenic role of these microorganisms in fish kept under confined condition.