Abstract

1. *NAMULAWA Victoria Tibenda1., KATO Charcles Drago2, NYATIA Edward2, RUTAISIRE Justus1, BRITZ Peter3 1Aquaculture Research & Development Centre, 530, Kampala Uganda 2Collage of Veterinary Medicine, Animal Resources & Bio-Security, Makerere University, 7062 Kampala Uganda 3Department of Ichthyology & Fisheries, Rhodes University 6140, Grahamstown South Africa Abstract The morphology of the gastrointestinal tract of adult Nile perch was described using standard SEM procedures. Investigations revealed the presence of cardiform teeth in the oral cavity, goblet cells and finger print-like microridges on the hard palate and oesophagus lumenal surface. Elaborate patterns and bacterial cells were observed on the stomach lumenal surface and intense foldings in the intestinal region. These observations provide a better understanding of the morphology of the gut in Nile perch and how it is suited for its digestive function. Introduction The anatomical characteristics of digestive system depend upon the food, habitat, and nutritional status of the organism (Delashoub et al., 2010). In fish, the morphology of the gastrointestinal tract explains how food is acquired, ingested, digested and assimilated (Sweetman et al., 2008). Nile perch (Lates niloticus) is a freshwater carnivorous fish occurring commonly the Lake Victoria basin and along the Nile River system (Hopson, 1972). Limited information is documented about the morphology of its digestive system (Nakamya, 2003; Namulawa et al., 2011), which limits the understanding of how this system functions. The objective of this study was therefore to examine the surface architecture of the gastrointestinal tract of Nile perch so as to better the understanding of features of this tract in relation to its function. Scanning Electron Microscopy of the Gastrointestinal tract of Nile perch (Latesniloticus, Linneaus, 1758) Nile perch sub adult Methodology Sample collection Nile perch adults (3- 5kg) were collected from Lake Victoria in Uganda, in waters around Kiggungu fish landing site, located 32ᵒ 26′ 15″E, 00ᵒ 2′ 49″N using long lines (hook No. 4 – 9). Laboratory procedure The oral cavity was accessed by examining the head. The head was exercised with a sharp knife just behind the operculum and fixed in 10% formalin followed by 100% alcohol for three days before they were air dried. Then socked in bleach (1% Sodium hypochlorite) to soften the tissues attached to the bones. Teeth patches from the vomer, premaxilla, palatine, pterygoid, dentary, tongue, gill rakers and pharynx were teased out and air dried and then critical dried for 1½ hours. Gut section was accessed by dissecting live samples (sedated with clove oil) through an abdominal incision to reveal the digestive system. Small pieces (2 x 4 mm) of gut sections (tongue, oesophagus, stomach, intestine, and liver) were fixed in 2.5% gultaldehyde buffered in 0.1M phosphate in 2ml epindorfs. The soft gut pieces were dried in alcohol of increasing concentration (30%, 50%, 70%, 80% 90%, 100%), and then critical point dried for 1½ hours. The critical dried gut and teeth specimens were each mounted onto aluminium studs and gold sputtered in a Balzer Union sputtering Device model FL-9496 for 40 minutes. The gold sputtered specimens were then scanned using a Vega TESCAN Scanning Electron Microscope Model TC100, at a high voltage of 20.00KV. Results SEM Micrographs Conclusion and discussion • Oral cavity has cardiform teeth, with sharp monocuspid tips, wedge shaped- obliquely tunicate flattened crowns that bend towards the tip. These enable Nile perch to capture live prey, to effectively hold and push it down the oesophagus without breaking into pieces. • The oesophagus surface cells are irregular with finger print-like micro-ridges, covered with a layer of mucus and bacterial cells . The musuc eases swallowing by reducing friction, while the ridges play an important role of protecting the buccal-oesphageal surface from trauma and providing an anchor to the mucus secreted from the goblet cells • Different patterns of folds occur on the stomach lumenal surface in the different stomach regions. These complex foldings provide for the extension of the stomach capacity during ingestion and increase the surface area during digestion. • Mucus, gastric pits and bacterial cells commonly occur in all the stomach regions . • Mucus is for chemical protection while the gut bacteria are a possible source of amylase, cellulose, lipase and protease. They are also important for in hydrocarbon degradation, chemical digestion and defence. • The ceaca and intestine lumenal surfaces are greatly folded and covered with mucus. • The mucus protects the surface against chemical digestion while the folds are a means of increasing the surface area of assimilation in this region. 1 4 7 GB 2 5 8 3 6 9 References Delashoub M, Pousty I, Khojasteh SM (2010). Histology of Bighead carp (Hypophthalmichthys nobilis) intestine. Global Veterinaria, 5: 302 -306. Nakamya MF (2003). A histomorphological study of the digestive system of the Nile perch. Bachelors of Biomedical Laboratory Technology (BBLT) Project Report, Makerere University, Kampala, Uganda. Namulawa VT, Kato CD, Nyatia E, Britz P, Rutaisire J (2011). Histomorphological description of the digestive system of Nile perch (L. niloticus). Int. J. Morphol., 29 (3): 723-732. Sweetman J, Dimitroglou SD, Torrecillias S (2008). Nutrient Uptake: gut morphology, a key to efficient nutrition. International Aquafeed, 26 - 30. 1: Oral; teeth 2: Surface of the soft palate, notice the goblet cell (GB); 3: Oesophagus lumen surface., notice the mucus patches (MP) , the polygon-shaped surface cells (SC) with finger print-like micro ridges (MR) and the star- shaped bacteria; 4: Lumenal surface in the stomach cardiac region; 5: Lumenal surface of the f stomach fundic region, notice the undulating pattern; 6: Lumenal surface of the posterior section of the fundic stomach region , notice the honey comb-shaped pattern; 7: Lumenal surface of the stomach blind end region, notice the surface mucous, the gastric pit openings, and bacteria; 8: Lumenal surface of the caeca, notice the folding of the lumen surface; 9:Lumenal surface of the anterior intestine, notice the folding of the lumen surface