Morphology, histology and histochemistry of the digestive tract of the Banded tilapia, Tilapia sparrmanii (Perciformes: Cichlidae)

ABSTRACT This study described anatomical, histological and histochemical features of the mucosal layer of the digestive tract of Tilapia sparrmanii Smith, 1840, an omnivorous freshwater fish endemic to Southern Africa. This species exhibited a short thick oesophagus with long deep longitudinal folds (466.68 ± 16.91 µm), and a thick (173.50 ± 10.92 µm) muscular layer that allow the passage of large food items. The mucosa was lined with stratified secretory epithelium rich in goblet cells that secreted neutral and acid mucins. The stomach was a sac-like structure with simple tubular glands surrounded by connective tissue. The mucosa was lined with simple columnar epithelium and the lamina propria exhibited a well-developed layer of gastric glands that occupied the entire length of the cardio-fundic region. The stomach mucosa consisted of epithelial cells with intense neutral mucin secretion which protects against gastric juice. Neck cells of gastric glands synthesized neutral and acid mucins. The intestine was highly coiled and presented a complex pattern of transversal folds internally (villi). Villi length decreased progressively from the anterior to the posterior intestine (p < 0.0001). Tunica muscularis of the mid-intestine had the thinnest thickness among all parts of the intestine (p < 0.0001). Goblet cells whose numbers increased towards the rectum secreted both acid and neutral mucins. The results indicate structural similarities of T. sparrmanii GIT with other tilapia species and will be useful for understanding the physiology of the digestive systems as well as functional components of the GIT.摘要 本研究对1840年Smith定名的南非特有杂食性淡水鱼类斯氏非鲫（Tilapia sparrmanii Smith, 1840）消化道黏膜层的解剖学、组织学及组织化学特征进行了系统记述。该物种具有短粗的食道，食道带有长而深的纵行褶皱（褶皱高度为466.68 ± 16.91 μm），且肌层发达（厚度达173.50 ± 10.92 μm），可保障大型食物颗粒顺利通过。食道黏膜被覆富含杯状细胞的复层分泌上皮，杯状细胞可分泌中性黏蛋白与酸性黏蛋白。胃呈囊状结构，其单管状腺体由结缔组织包被。胃黏膜被覆单层柱状上皮，固有层中可见发育良好的胃腺层，该胃腺层覆盖了贲门-胃底区域的全长。胃黏膜上皮细胞可大量分泌中性黏蛋白，以抵御胃液的侵蚀。胃腺的颈细胞可合成中性与酸性黏蛋白。肠道高度盘曲，内部具有复杂的横向褶皱（即肠绒毛）结构。肠绒毛长度从前肠至后肠逐渐缩短（p < 0.0001）。中肠的肌层厚度在肠道各段中最薄（p < 0.0001）。杯状细胞可分泌酸性与中性黏蛋白，且其数量随肠道向直肠方向逐渐增多。本研究结果表明，斯氏非鲫的胃肠道（gastrointestinal tract, GIT）结构与其他罗非鱼物种存在结构相似性，该结果可为阐明消化系统生理学及胃肠道功能组分提供重要参考依据。