Morphological characteristics of the digestive tract of gnotobiotic Artemia franciscana nauplii R.A.Y.S. Asanka Gunasekara a , Anamaria Rekecki a , Pieter Cornillie a , Maria Cornelissen b , Patrick Sorgeloos c , Paul Simoens a , Peter Bossier c , Wim Van den Broeck a, ⁎ a Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820, Merelbeke, Belgium b Department of Basic Medical Sciences, Faculty of Medicine and Health Sciences, De Pintelaan 185 6B3, Ghent University, 9000 Ghent, Belgium c Laboratory of Aquaculture and Artemia Reference Center, Ghent University, Rozier 44, 9000 Ghent, Belgium abstract article info Article history: Received 5 April 2011 Received in revised form 22 July 2011 Accepted 28 July 2011 Available online 9 August 2011 Keywords: Gut Gnotobiotic Microscopy Artemia Morphology Cysts of Artemia franciscana were hatched and nauplii were reared under gnotobiotic conditions (gnotobiotic Artemia rearing system). Stereomicroscopy, computer assisted three-dimensional reconstruction, light microscopy, and transmission electron microscopy were used to study the structural and cellular morphology of their digestive tracts. The alimentary tract of gnotobiotic Artemia nauplii, fed with dead Aeromonas hydrophila and wild type strain of Saccharomyces cerevisiae, is a hooked, tubular structure which is composed of three clearly distinguishable parts, i.e. the foregut, midgut and hindgut that are freely suspended in haemolymph. The epithelium lining of the entire gut consists of a single cell layer. Enterocytes of the foregut and hindgut are cuboidal and lined by a thin cuticle, whereas midgut enterocytes are cuboidal to columnar and possess an apical brush border. The fore- and hindgut mainly display characteristics suggestive for mechanical functions, whereas the midgut shows characteristics of absorption, storage and secretion. The gnotobiotic Artemia rearing system is most useful to investigate the effects of micro-organisms on the development of nauplii. The knowledge acquired in this study potentially facilitates the evaluation of gut morphology when specific micro-organisms are introduced into the culture system, as compared to the gnotobiotic counterparts. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Successful aquaculture is still hampered by diseases of the larval phases, leading to massive mortalities and considerable economic losses (Marques et al., 2005). Antibiotic therapy and disinfectants have only had limited success in the prevention or cure of aquatic diseases (Defoirdt et al., 2004). Moreover, the frequent use of these chemicals results in rapid development of resistance (Dias et al., 1995; Molina-Aja et al., 2002; Vattanaviboon et al., 2003; Vivekanandhan et al., 2002). Therefore, it is of major importance to have alternative disease control techniques in aquaculture, focusing especially on prevention, which is likely to be more cost-effective than curative treatments (Subasinghe, 1997). Managing microbiota in larvae aquaculture is an effective preventive strategy. Hence, the study and control of harmful micro- organisms and the promotion of beneficial micro-organisms are of utmost importance. A powerful experimental approach to study the function of the microbiota uses a gnotobiotic rearing system in which animals are reared in germ-free conditions and monitored after introducing defined microbes (Falk et al., 1998). Although many studies are performed with gnotobiotic terrestrial animals, studies with gnoto- biotic aquatic organisms are still scarce. Some constraints hampering the wide use of these organisms in research are the need for disinfection methods to produce germ-free organisms and difficulties in assuring the complete germ-free condition of a culture system (Marques et al., 2006). A successful step forward in the development of such an aquatic gnotobiotic model was made more than twenty years ago when Sorgeloos et al. (1986) and later Marques et al. (2004a) described a gnotobiotic Artemia rearing system to obtain sterile Artemia cysts and nauplii. Future studies of host–microbe interactions using gnotobiotic aquatic animals should consider possible parameters, such as survival, growth, immunological re- sponse and histological development (Marques et al., 2006). The present study is aimed especially at the morphology of the gnotobiotic Artemia nauplii. Although the gut morphology of conventional Artemia nauplii was studied in detail using transmission electron microscopy a few decades ago (Hootman and Conte, 1974), to our knowledge, this is the first descriptive study illustrating the digestive tract morphology of gnotobiotic Artemia franciscana nauplii. The present study aims to describe the histology, the three-dimensional architecture, and the cellular morphology of the gut of gnotobiotic Artemia nauplii during Aquaculture 321 (2011) 1–7 ⁎ Corresponding author. Tel.: + 32 92647716; fax: + 32 92647790. E-mail address: wim.vandenbroeck@UGent.be (W. Van den Broeck). 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.07.037 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online