Studies On The Ontogeny Of Digesitive Systemand The Effect Of Starvation And Refeeding On Digestive System Of Juvenile Red Swamp Crayfish(Procambarus Clarkii)

The red swamp crayfish(Procambarus clarkii) is an important freshwater shrimp species, which is widely and well liked by the people because of its delicious and nutritious meat. Although several studies were involved in the nutrition and biological invasions of P. clarkii, little informantion was available about the ontogeny of digesitive system and the effect of starvation on the ontogeny. In this study, the ontogeny of digestive system and the effect of different term of starvation and refeeding on the structure and enzyme activities of digestive system were investigated by morphohistology observation, ultrastructure research and enzyme activity detection, so as to learn the digestive physiological characteristics of larval and juvenile P. clarkii. The results of the present study would provide theoretical basis for the high-efficiency feed development and feeding regimes.1. The present study was conducted to determine the ontogenetic development of the digestive tract and hepatopancreas in larval P. clarkii after hatching by the histological and ultrastructural approcaches. Based on food sources, external morphology and features of the digestive system, development of larval P. clarkii could be divided into three stages from hatching: I stage larva(1DAH-4DAH), II stage larva(5DAH-8DAH) and III stage larva(9DAH-12DAH). In I stage larvae: cardiac stomach and pyloric stomach, which were surrounded by yolk sac, showed a simple cystic form with a gastric mill prototype in cardiac stomach and the occurance of the gland filter in pyloric stomach; a few small vacuoles in the anterior region of midgut and abundant vacuoles in the posterior region of midgut were observed, and there was a middle region of midgut which only arose in I stage larva; gut wall of hindgut closely connected to muscle. In II stage larva, the structure of stomach became complicated, in which the grooves, chamber, esophagus-cardiac stomach valve arose; the gastric mill was observed in cardiac stomach; increasing quantity of vacuoles in anterior region of midgutwere observed, whereas the vacuoles in the posterior region was lost.. In III stage larva, the digestive system has well developed and was similar to those in adult P. clarkii. II stage was the most active period during development of digestive system.2. In present study, our center destination is to evaluate the effect of starvation of 20 day on growth, survival rate, and the histomorphological and ultrastructure changes of digestive system in juvenile P. clarkii. During the experiment, juvenile P. clarkii were separated into two groups: food-deprived group and control group. Individuals were collected at 14, 20, 29 DAH(day after hatching). After 20 days of fasting, the total body weightfluctuated at 10.17 mg, the total body length fluctuated at 8.12 mm, and the mortality of crayfish was zero. The results of histomorphological changes of digestive system showed that the esophagus and stomach wall was thinning, the epithelium atrophied to cuboidal, nuclei was darker and smaller, and nucleolus was difficulty to observe, the midgut and hindgut of larvae showed wider volume, thinning wall, atrophied epithelial and muscularis and shorter ridges, and hepatopancreas tubule lumens of fed-deprived group were wider, the lipid droplets in R-cells were smaller and less, and the quantity of typical B-cells decreased, after 20 days of starvation. The results of ultrastructure changes showed that the mitochondria of midgut epithelium and R-cells were swollen and vacuolated, and the ridges of which were fractured and reduced. In addition, the electron density of cytoplasmic matrix of R-cells decreased, and the quantity of glycogen granules and lipids also decreased. Ultrastructure changes of B-cells were similar to those of R-cells. Signs of degeneration in histological structure and function of digestive organs were significant during starvation, and juvenile P. clarkii was able to endure short-term starvation.3. The ontogenesis of digestive enzymes and alkaline phosphatase and the effect of starvation and refeeding on activities of digestive enzymes, and alkaline phosphatase and the height of gut ridge were investigated in juvenile P. clarkii. All of assayed digestive enzymes were detected in juvenile P. clarkii. In the control group, the activities of trypsin and alkaline phosphatase increased, the activities of amylase and pepsin increased firstly then decreased, and the activity of lipase increased firstly and then decreased and then increased again during the development period of juvenile P. clarkii(0-29 DAH). Refeeding after 7 days fasting, the weight of juvenile P. clarkii showed exponential growth. In refeeding groups after 7 days fasting and 14 days fasting, molting was observed, and the molting time was consistent with the development group. In food-deprived groups, activities of pepsin and lipase both decreased(P<0.05) after fasting, and the activities of pepsin, lipase and trypsin all increased(P<0.05) again after refeeding. However, the activity of amylase increased(P<0.05) in food-deprived group, and then decreased after refeeding. The activity of alkaline phosphatase did not significantly(P>0.05) vary after fasting, whereas after refeeding, alkaline phosphatase activity showed an decreasing first and then increasing trend and was similar with the control group finally. In crayfish refeeding after 7 days fasting, the height of midgut ridge increased, and showed no significant difference(P>0.05) when compared with the control group, and the height of hindgut ridege increased either, which was significantly lower than control group at 23 DAH, and showed no significant difference(P>0.05) when compared with the control group at 30 DAH. In refeeding after 14 days fasting, the height of midgut ridge increased, and was significantly lower(P<0.05) than control group at all the sampling time, so did the height of hindgut ridge.