| This dissertation investigated the distribution and features in the different digestive organs of the digestive enzymes (protease, amylase) activity and analysised the effect of pH and temperature on digestive enzymes activity of grey mullet in different growing environments, while the digestive system histology were compared of the wild and cultivated grey mullet. Effects of salinity stress to gill Na+/K+-ATP activity (NKA) activity, body moisture, gill and kidney structure on juvenile mullet were reseached, and effects of salinity stresses and diurnal variation on digestive enzyme activity of juvenile grey mullet M. cephalus were studied.The results showed as follows:1 Comparative study on the digestive enzymes activity of wild and cultivated M. cephalusThe digestive tube index and the activity distributions of the digestive enzymes in the digestive organs of wild and cultivated M. cephalus were studied in this paper, And the effects of different temperature and pH on digestive enzyme activity were studied in both populations. The results showed that in the wild and cultivated grey mullet, the ratio of intestine gut length to body length were 2.886±0.301 and 3.315±0.141 while the ratios of viscera, liver and stomach weight to body weight were 0.043±0.001 and 0.048±0.004, 0.009±0.001 and 0.007±0.000, 0.008±0.002 and 0.007±0.000, respectively. In the wild and cultured grey mullet, the activity of protease in different organs were in the order of hindgut > foregut > midgut > hepatopancreas > stomach and foregut > midgut > hindgut > hepatopancreas > stomach,while amylase in the order of hindgut > pyloric caecum > midgut > foregut > hepatopancreas > stomach and pyloric caecum > foregut > midgut > hindgut > stomach > hepatopancreas. The results showed that the digestive enzymes activity of wild grey mullet is stronger than the cultured group and the differences of protease activity in hepatopancreas and stomach between the two populations were not significant(P>0.05), while in midgut the difference was significant (P<0.05). In foregut and hindgut, the protease activity were extremely significant(P<0.01). The differences of amylase activity in every part between the populations were extremely significant (P<0.01). The digestive system of grey mullet compartmentalized the six parts were hepatopancreas, stomach, foregut, midgut, hindgut and pyloric caecum. The results showed that, the amylase to wild grey mullet, the optimum temperatures were 40, 45, 45, 45, 40, 45℃and the optimum pH in hepatopancreas was 4.2 and in others were 7.2. For cultured grey mullet, the optimum temperatures of the amylase were 40, 40, 40, 45, 40, 40℃and the optimum pH in stomatch and foregut were2.2 and 8.0, and in other tissues was7.2. To wild grey mullet, the optimum temperature of protease in hepatopancreas, stomach, midgut and hindgut was 45℃, while in foregut was 50℃and the optimum pH of protease in stomach was 3.2, and in others were 7.2 of the both populations. and to cultured grey mullet, in hepatopancreas, stomach and midgut was 40℃, while in foregut and hindgut was 45℃.2 The effect of salinity stresses and diurnal variation on digestive enzyme activity of juvenile M. cephalusStudies were conducted on the effect of salinity stresses and diurnal variation on protease and amylase activity of juvenile M.cephalus. Five different salinities were set which were S0(salinity was 0), S10, S20, S33(control) and S40 respectively. The results indicated: (1) Salinity stresses had significant effects on specific activities of digestive enzymes(P<0.05). The variation on different salinity changes of digestive enzyme activity was increased in 0d to 7d, then 7d to 14d depressed. The change trend of protease activity was S0 to S33 up, S33 to S40 down. The difference of amylase activity in S0 to S20 was non-significant(P>0.05); while in S20 to S33 was increased and S33 to S40 was depressed, the difference among three groups(S20, S33, S40) were significant each other (P<0.05). (2)The study on the diurnal variation of digestive enzyme activity of M.cephalus showed that the highest activity of protease and amylase appeared at 12:00 and 15:00, respectively, while the lowest activity of protease and amylase all appeared at 6:00.3 Studies on histology of digestive system of wild and cultivied M. cephalusThe results showed that there were some diferences between the wild and cultivated types in the shape and histologyof digestive system. (1) In terms of morphology, oesophagus was crude and short; the spherical stomach was divided into four portions, they were the cardia, gastric caeca, fundic stomach and pyloric part. There was a two finger pyloric caeca intestine was circled 5 laps in the abdominal cavity. Brown liver, right lobe was larger than the left lobe, single pancreas was not found.With cultivated mullet, the digestive tract was wrapped more fat, the stomach smaller but bigger stomach cavity. Intestinal was longer than wild mullet. Meanwhile the average intestinal coefficient of was M. cephalus calculated , which came to about 2.909 and 3.080 to wild and cultivated mullet. (2) Histological studies have shown that:there were two regions in the oesophagus, including cranial with pavement epitheliums and caudal with simple columnar epitheliums, and muscularis mucosa was thicker; in wild mullet, the surface of esophageal mucosa was covered with keratinocytes,and longitudinal muscle was thicker.stomach had a single-layered columnar epithelium under whichin the the mucosa of cardiac and fundic portion well-developed gastric glands and gastric pits were present. The mucosal folds and small mucosal fold in cultivated mullet was higher than the wild mullet. The mucosa of fundic stomach was composed of stratified squamous epithelium with many goblet cells, the muscle of fundic stomach and pyloric part was almost the entire thickness of the stomach, and the wild mullet was thicker than cultivated. The histological features of pyloric caeca was similar to the cranial intestine's. The intestine epithelium was composed of simple columnar cells with a distinct brush border, in which there were many goblet cells. Meanwhile the distribution trends in the whole intestine was:hindgut > foregut > midgut and cultivated mullet > wild mullet. The mucosal folds of wild mullet was showing irregular branch-like, and non-branching strip to cultured mullet. The liver lobule was not clear but its hepatic cell cord was obvious. The pancraes distributes in the surrounding mesentery around the stomach,gut and bile duct.4 The Effects of Salinity Stresses on Na+/K+-ATPase(NKA)in Gills and Body Moisture of the Juvenile M. cephalusIn this paper, the gill Na+/K+-ATPase(NKA)activity and the body moisture con- cent in juvenile M. cephalus were investigated in a 12 d stress of ambient salinities (0～40). The results showed that the mortality rate of the juvenile grey mullet were 31.7%, 28.3%, 6.7%, 3.3% and 13.4%, respectively when the fishes were transferred from control group(salinity was 33) into treatment S0(salinity was 0), S10, S20, S33 (control) and S40 suddenly. The gill NKA activity fluctuated in first 3 d, and then changed smooth1y in all treatments.At the end of the experiment(12 d), the NKA activity varied with salinity grade in "∩"shape being significantly (P<0.05) higher in salinity 10, 20 and the lowest in salinity 33.The body moisture content of removing visceral group and whole fish group were S0 > S20 > S10 > S33 > S40 and S20 > S0 > S10 > S33 > S40, respectively. All the results revealed that the juvenile grey mullet could adapt to different salinity environment in 9 days. Comparing with the removing visceral group (14 d), the moisture content of whole fish group (12 d) was higher in the stable period, except the S0 treatment group.5 Structural changes in gill and kidney of juvenile M.cephalus under salinity stress The gill and kidney structure of juvenile grey mullet M. cephalus has been observed under different salinities level by using the technology of histological photomicrography. The relationships between structural changes and osmitic regulation are also discussed. The result has shown that, (1) with salinity increased, gill lamellae gradually became narrows, the spacing becomes smaller. In contrast to different groups showed a marked increase inthe number and size of chloride cells. On the lamellae of these fish,chloride cells Were generally centralizing to the base of lamellae, and spreading to both sides. At the high-salt group (S40), gill lamellae epithelial appears separation and off phenomenon. (2) structures of glomerular and tubular at all levels have been shrineled at varying degrees with salinity increased. |
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