Morphological characteristics of the digestive tract of gnotobiotic Artemia franciscana nauplii

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.