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ABSTRACT
This study investigated the anatomy and histology of the digestive tract of a rare annual fish, Hypsolebias antenori captured from seasonal freshwater pools located in Northeastern Brazil. Scientific information about this rare species is very limited. The digestive tract of H. antenori shows a dorsally situated mouth, small conical teeth, first branchial arch with anatomically visible gill rakers, a short tubular esophagus constituted by pseudo stratified epithelium and lamina propria, stomach with cardiac, fundic and pyloric regions, and an intestine which opens out through the anus. The three stomach regions are constituted by simple cylindrical epithelium with mucous cells. The stomach and intestine are well vascularized. The anterior part of the intestine has well developed folds, presence of goblet cells and glands for absorption, while the posterior part of the intestine lacks them. This pioneering study gives details about anatomical and histological characters of the digestive tract of H. antenori, which indicate omnivorous feeding habits.
Keywords: Hypsolebias antenori; annual fish; morphology; histology; digestive tract
INTRODUCTION
The family Rivulidae is one of the largest families of freshwater fish of the Neotropical region. It is a diverse group of annual fish, most popularly known as "killifish", which occurs in seasonal freshwater pools of tropical and subtropical areas of South America (Costa, 2011). Brazil has the greatest diversity of the family Rivulidae and is represented by 30 genera with approximately 120 species (Fricke and Eschmeyer, 2012). Despite the richness of killifishes, this family is considered rare and endangered in Northeastern Brazil (Nascimento et al., 2012). The annual fish complete their life cycle in temporary freshwater pools which dry out during the warm season, and as a result the entire population dies from desiccation (Wourms, 1972; Errea and Danulat, 2001; Nascimento et al., 2012). These temporary pools are environments that have large fluctuations in temperature, level of dissolved oxygen concentration and volume of water. To survive under these extreme conditions, the fish eggs deposited in the sediment of the pools go through diapause stages, during which time the embryonic development becomes temporarily arrested. With the onset of the next rainy season these eggs hatch out and a new generation is formed (Nascimento et al. 2012). Hypsolebias antenori (Costa, 2006) is an annual fish of family Rivulidae,...