AIM To identify the type localization andmorphology of APUD endocrine cells in thegastroenteropancreatic(GEP)system ofstomach-containing teleosts,and study APUDendocrine system in the stomach,intestine andpancreas of fish species.METHODS Two kinds of immunocytochemical(ICC)techniques of the streptavidin biotin-peroxidase complex(SABC)and streptavidin-peroxidase(S-P)method were used.Theidentification,localization and morphology ofAPUD endocrine cells scattered in the mucosa ofdigestive tract,intermuscular nerve plexus andglandular body of northern snakehead(Channaargus),ricefield eel(Monopterus albus),yellow catfish(Pelteobagrus fulvidraco),mandarinfish(Siniperca chuatsi),largemouthbass(Micropterus salmoides),orientalsheatfish(Silurus asotus),freshwater pomfret(Colossoma brachypomum)and nile tilapia(Tilapia nilotica)were investigated with 8 kindsof antisera.RESULTS The positive reaction of 5-hydroxytryptamine(5-HT)immunoreactiveendocrine(IRE)cells was found in the digestive tract and glandular body of 8 fish species indifferent degree.Only a few gastrin(GAS)-IREcells were seen in C.argus,M.albus and P.fulvidraco.Glucagon(GLU)-IRE cells were notfound in the digestive tract and glandular bodybut existed in pancreatic island of most fishspecies.The positive reaction of growthhormone(GH)-IRE cells was found only inpancreatic island of S.Chuatsi and S.Asotus,no positive reaction in the other 6 fish species.Somatostatin(SOM)-,calcitonin(CAL)-,neurofilament(NF)-and insulin(INS)-IRE cellsin the stomach,intestine and pancreas of 8 kindsof fish were different in distribution and types.The distribution of all 8 APUD cells was the mostin gastrointestinal epithelium mucosa and then indigestive glands.The positive reaction of SOM-and 5-HT-IRE cells was found in intermuscularnerve plexus of intestine of P.fulvidraco andS.chuatsi.Only GH-IRE cells were denselyscattered in the pancreatic islands of S.chuatsiand S.asotus,and odd distribution in thepancreas of S.asotus,SOM-IRE cells weredistributed in the pancreatic islands of S.asotus,C.Brachypomum and T.nilotica.There were INS-IRE cells in the pancreaticislands of S.chuatsi and S.asolus.Eightkinds of APUD cells had longer cell body andcytoplasmic process when they were located inthe gastrointestinal epithelium,and had shortercell body and cytoplasmic process in the gastricgland,and irregular shape in the esophagus andpancreatic island.CONCLUSION Eight kinds of IRE cells were identified in the GEP system of stomach-containing teleosts. These endocrine cells were scattered in gastrointestinal mucosa, intermuscular nerve plexus, gland body, pancreatic gland and islands under APUD system. CAL- and GH-IRE cells in the pancreatic islands of fishes showed functional diversity for these two hormones. Their morphological feature provides evidence of endocrine-paracrine and endocrine-exocrine acting mode. This research can morphologically prove that the GEP endocrine system of fish ( the lowest vertebrate) is almost the same as of mammal and human. AIM To identify the type localization andmorphology of APUD endocrine cells in the gastroenteropancreatic (GEP) system of lung-containing teleosts, and study APUDendocrine system in the stomach, intestine and pancreas of fish species. METHODS Two kinds of immunocytochemical (ICC) techniques of the streptavidin biotin- peroxidase complex (SABC) and streptavidin-peroxidase (SP) method were used. The identification, localization and morphology of APUD endocrine cells scattered in the mucosa ofdigestive tract, intermuscular nerve plexus andgular body of northern snakehead (Channaargus), ricefield eel (Monopterus albus), yellow catfish (Pelteobagrus fulvidraco), mandarinfish (Siniperca chuatsi), largemouthbass (Micropterus salmoides), orientalsheatfish (Silurus asotus), freshwater pomfret (Colossoma brachypomum) and nile tilapia (Tilapia nilotica) were investigated with 8 kinds of antisera .RESULTS The positive reaction of 5-hydroxytryptamine (5-HT) immunoreactive endocrine (IRE) cells was found in the digestive tract and gl andular body of 8 indifferent degrees of fish species.Only a few gastrin (GAS) -IREcells were seen in C.argus, M.albus and P.fulvidraco.Glucagon (GLU) -IRE cells were notfound in the digestive tract and glandular bodybut existed in pancreatic island of most fishspecies. The positive reaction of growthhormone (GH) -IRE cells was found only in pancreatic island of S. Chanatsi and S. Asotus, no positive reaction in the other 6 fish species. Somatostatin (SOM) -, calcitonin ( CAL) -, neurofilament (NF) -and insulin (INS) -IRE cellsin the stomach, intestine and pancreas of 8 kinds of fish were different in distribution and types. The distribution of all 8 APUD cells was the mostin gastrointestinal epithelium mucosa and then indigestive glands. The positive reaction of SOM-and 5-HT-IRE cells was found in intermuscular nerves plexus of intestine of P. fulvidraco and S. chuatsi. Ofly GH-IRE cells were densely scattered in the pancreatic islands of S. chuatsiand S. asotus, and odd distribution in the pancreas of S.asotus, SOM-IRE cells weredistributed in the pancreatic islands of S.asotus, C.Brachypomum and T. nilotica.There were INS-IRE cells in the pancreaticislands of S. chuatsi and S.asolus.Eightkinds of APUD cells had longer cell body andcytoplasmic process when they were located inthe gastrointestinal epithelium, and had shorter cells body and cytoplasmic process in the gastricgland, and irregular shape in the esophagus and pancreatic island. CONCLUSION Eight kinds of IRE cells were identified in the GEP system of stomach-containing teleosts. These endocrine cells were scattered in gastrointestinal mucosa , intramuscular nerve plexus, gland body, pancreatic gland and islands under APUD system. CAL- and GH-IRE cells in the pancreatic islands of fishes showed functional diversity for these two hormones. Their morphological feature provides evidence of endocrine-paracrine and endocrine-exocrine acting mode. This research can morphologically prove that the GEP endocrine system of fish (the lowest vertebrate) is almost the sa me as of mammal and human.