Effects of mass and position of artificial fouling added to the upper valve of the mangrove oyster Crassostrea rhizophorae on its growth and survival César Lodeiros a, ⁎ , Lee Galindo b , Esperanza Buitrago c , John H. Himmelman d a Lab. Acuicultura, Instituto Oceanográfico de Venezuela, Universidad de Oriente, Cumaná 6101, Venezuela b Postgrado en Ciencias Marinas, Universidad de Oriente, Cumaná 6101, Venezuela c Estación de Investigaciones Marinas de Margarita, Fundación La Salle de Ciencias Naturales, Isla Margarita, Venezuela d Département de biologie, Université Laval, Quebec City, Canada G1K 7P4 Received 18 March 2006; received in revised form 30 September 2006; accepted 1 October 2006 Abstract We ran an experiment on mangrove oysters Crassostrea rhizophorae to evaluate the effects of adding different masses of artificial fouling to the upper valve, either to the umbo region or the ventral edge of the shell. Growth and survival were quantified after a 30 d period in suspended culture in the La Restinga Lagoon, Venezuela. The artificial fouling was cement weighing 0.5, 1, 2 or 3 fold the mass of the upper valve. No fouling was added to a control group. Fouling mass, but not the position of the artificial fouling, affected growth in shell length. However, only the heaviest fouling (3 times the mass of the upper valve) had a significant effect. In contrast, there was no affect of either fouling mass or position on tissue growth. Finally, our data indicated that mortality could be affected by the position where we added artificial fouling (greater mortality when fouling was added to the ventral edge of the shell), but not by fouling mass. Our study indicates it is unlikely that the levels of natural fouling that develop on oysters in suspended culture would be sufficient to affect either growth or survival. © 2006 Published by Elsevier B.V. Keywords: Oyster culture; Venezuela; Fouling; Crassostrea rhizophorae 1. Introduction The growth of fouling organisms often leads to decreases in the growth and survival of bivalves in suspended culture (Ventilla, 1982; Vélez et al., 1995; Lodeiros and Himmelman, 1996, 2000; Loderios, 2002), or reduces the value of the cultured species (Ventilla, 1982). Some of the negative effects of fouling are related to the reduction of water flow through culture enclosures, as reduced flow could decrease the availability of food particles, reduce oxygen levels, or limit the dispersal of waste products (Côté et al., 1994; Ross et al., 2002). In addition, fouling organisms could compete for food particles (Claereboudt et al., 1994; Lodeiros and Himmel- man, 1996, 2000). For bivalves, another possible effect of fouling is that it may interfere with the opening and closing of valves (Lodeiros and Himmelman, 1996, 2000). This is most likely for bivalve species that lie on one side, such as oysters and scallops, as the fouling would add to the force needed to lift the upper valve. In contrast, fouling on bivalves such as mussels and pearl oysters, which are positioned vertically with the valves to the left and right, Aquaculture 262 (2007) 168 – 171 www.elsevier.com/locate/aqua-online ⁎ Corresponding author. Tel.: +58 293 302124. E-mail address: cesarlodeirosseijo@yahoo.es (C. Lodeiros). 0044-8486/$ - see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.aquaculture.2006.10.002