Morphology of The Digestive Tract of The African Catfish(Clarias gariepinus Burchell, 1822)

Abstract

The teleost digestive tract is simple and comprises the following parts: oropharyngeal cavity, oesophagus, stomach, intestine, rectum and anus. These organs are involved in the breakdown of ingested food macromolecules into small absorbable micromolecules. These small molecules are necessary for the maintenance, growth and energy needs of the body (Johnson, 1994; Junqueira and Carneiro, 2005). Besides processing food, some parts of the tract have evolved into organs of respiration (proximal intestine), osmoregulation (oesophagus, distal intestine and rectum) and carbon sequestration, thus contributing to the ocean inorganic carbon cycle (Cataldi et al., 1988; Grau et al., 1992; Park et al., 2003; Gifford-Mena et al., 2006; Wood et al., 2007; Grosell, 2011). Teleosts are classified into herbivores; omnivores and carnivores based on the nature of food taken and the morphology of the digestive apparatus are adapted to their food and feeding habits (Bucke, 1971; Verma et al., 1974; Anderson, 1986; Russo et al., 2007). This effect is seen in the relative length of the tract, especially the intestinal length – hence the intestinal length often, is an indicator of diet, even though in some species, there is positive allometric relationship between intestinal length and body size (Kramer and Bryant, 1995a). Species that eat only algae or higher plants (herbivores) tend to have longer intestines than species that eat both plant and animal materials (omnivores), and these in turn tend to have longer intestines than species that are carnivores (Al-Hussaini, 1947, 1949; Fryer and Iles, 1972; Kapoor et al., 1975; Kramer and Bryant, 1995b). Intestinal length also varies between sexes like in Rhodeus sericeus amarus (Dumitru and Mihal, 1962). Diet variation may reflect variation in the gut morphology, even within the same genus (Elliott and Bellwood, 2003). Also the presence of ‘gizzard’ or some other structures in the fore part of the tract like pharyngeal pad and teeth, pharyngeal or oesophageal sacs which triturate the food, influences the differences in relative gut-length (Verighina and Medani, 1968; Verighina, 1969; Linser et al., 1998). In stomachless fish, the intestine is the most developed organ of the tract (Salvador-Jr et al., 2009).