PRELIMINARY OBSERVATION ON THE MORPHOLOGY AND HISTOLOGY OF THE ALIMENTARY TRACT OF THE CHINESE PADDLEFISH PSEPHURUS GLADIUS(MARTENS)

The Chinese paddlefish is one of the rare fishes in the world. Just on the ventral surface of the semitranslucent sword-shaped snout, it has an inferior bell-shaped mouth which can protrude for predation. The buccopharyngeal cavity is big with fine teeth located at the floor and roof of the skin. A pair of spiracles are present in the roof as well. The opercular flaps are well-developed and the gill takers are on the sides of the gill arch, forming dense network.Thus, the structure of the cavity is adequate for capturing and filter-feeding. Like most of carnivorous fish, the digestive tract of the Chinese paddlefish is short but complex. It can be divided into esophagus, backward limb of stomach, forward limb of stomach, small intestine, valvular intestine(containing valvula spiralis), rectum and anus. No demarcation line is recognized between esophagus and stomach. The pneumatic cyst attaches and opens to the region of esophagus-gaster transition. Pneumatic duct is not visible outside. Pyloric caecum has no, division or lobes and provides hardly space for chyme. In the conjunction between small and valvular intestine, a particular lymphatic organ is present. There are abdominal pores on each side of the anus and a cloacal orifice on the back extremity. Goezia(Goezia)sp. and a species belonging to acanthocephala parasites in the tract have been found also.The buccopharyngeal cavity is covered by stratified squamous epithelium in which there are mucus-secreting cells and granular cells. Taste buds are found in the skin of the roof and floor of the cavity, also found around the mouth corner, barlets and nearby area. The tract after pharynx consists of mucous membrane(without muscularis mucosae), submucosa(absence in the small intestine and the fore part of valvular intestine), lamina muscularis and adven-titia. The fore part of esophagus bears stratified squamous epithelium, in which there are flat cells having netlike microridges and mucus-secreting cells. The tract posterior to the fore part of esophagus is corved by simple columnar epithelium in which ciliary columnar cells are distributed. The simple columnar cells with microvilli in the rear part of esophagus and stomach are secretory mucus cells and in intestine are absorbing cells(lacking in the rear part of small intestine, the rear part of valvular intestine and rectum). Goblet cells begin to appear in small intestine and become more and more backward. Goblet cells and secretory mucus cells contain glycogen. Wandering cells and granular cells are also found in the simple columna repithelium.The mucous membrane of small intestine is honeycombed. The core of the compact pyloric caecum is honeycombed as well. The distribution of the digestive gland is only confined to the tunia propria of the backward limb and a certain area of forward limb of stomach, while the tunia propria at other parts become stratum compactum. The lamina muscularis in the fore part of esophagus is mainly striated muscle and in the rest parts of the tract is smooth muscle. The cells covering on the adventitia are either columnar or cuboidal or flat.