Treatment of Microcotyle sp. (Monogenea) on the gills of cage-cultured red porgy, Pagrus pagrus following baths with formalin and mebendazole Pantelis Katharios * , Nikos Papandroulakis, Pascal Divanach Institute of Aquaculture, Hellenic Centre for Marine Research, PO Box 2214, Port of Heraklion, 71003 Crete, Greece Received 29 March 2005; received in revised form 25 May 2005; accepted 30 May 2005 Abstract Two bath treatment trials for the control of the monogenean Microcotyle sp. in the gills of cultured red porgy, Pagrus pagrus using formalin (200 ppm for 1 h) and mebendazole (400 ppm for 1 h) were conducted. Formalin was very effective removing all the parasites from the gills of the infected fish while mebendazole produced no significant result. Based on the results of the trial, formalin was selected for the treatment of a large population of heavily infected red porgies held in sea cages. The results of the treatment are discussed. D 2005 Elsevier B.V. All rights reserved. Keywords: Monogeneans; Microcotyle ; Bath treatment; Formalin; Mebendazole; Red porgy 1. Introduction The red porgy (Pagrus pagrus L. 1758) is a species of great commercial importance for the Mediterranean aquaculture industry, due to its high market demand, good growth rates and adaptability in culture condi- tions (Kentouri et al., 1995; Maragoudaki et al., 1999; Papandroulakis et al., 2004). The main drawbacks for the extensive commercial production of this species are associated with its skin discoloration (Pavlidis et al., 2002) and with diseases including bacterial, viral and parasitic infections. One parasitic problem recent- ly observed in cage-cultured red porgy is the infesta- tion with the gill monogenean, Microcotyle sp. Monogenean parasites in wild fish usually occur in low numbers presenting few, if any problems to the host. However under culture conditions Monogeneans such as Microcotyle sp. can cause serious problems to the host from severe anaemia in the gills, reduced growth performance, loss of appetite and mortalities (Faisal and Imam, 1990; Ramasamy et al., 1995). Mortalities, severe gill anaemia and reduced growth were recorded in heavily parasitized by microcotylid 0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.05.046 * Corresponding author. Tel.: +30 2810 241892; fax: +30 2810 241882. E-mail address: katharios@imbc.gr (P. Katharios). Aquaculture 251 (2006) 167 – 171 www.elsevier.com/locate/aqua-online