| Chum salmon(Oncorhg chus keta Walbaum) was the world's valuable fish,and produced in Heilongjiang River,Suifenhe(its tributaries of Heilongjiang River) and Tumen River,it plays an important economic status in Heilongjiang Fisheries.Nowadays,the world reserves of chum salmon resources decline,so it was great significance that it carried out the protection of chum salmon resources and eco-physiological study,investigated the relevant theory and techniquesof artificial breeding,to conduct large-scale farming and breeding of chum salmon,improve the International impact of chum salmon biology and artificial breeding research in our country,to promote the recovery of salmon resources and ecological environment in Heilongjiang.In this study,it was the first time to study the activity of digestive enzymes and alkaline phosphatase,physiological and biochemical indexes of blood,the changes of stomach,intestinesand liver of young chum salmon under different salinities,and the existence and growth of young chum salmin in freshwater deeply and systematically.The results are as follows:1.Studies were conducted on the effect of salinity on protease,amylase,lipase and alkali phosphatase activity of young chum salmon(body weight:26.57±6.32g,total length:14.44±1.05cm) digestive organs which were stomach,pyloric caeca,intestines and liver.Five different salinities were set which were 0,5,10,15 and 20 respectively,and fish in freshwater served the control.The acute salinity experiments lasted for 130 days,and there were triplicates in each treatment.The results showed that:In 30 days,the activity of stomach protease and amylase were no significant difference(P＞0.05) in five salinity groups,intestinal protease activity of 10 group was significantly higher than that of 20(P＜0.05);in 130 days,stomach protease activity of 10 and 15 group was significant difference(P＜0.05),intestinal protease activity of 0 group was significantly higher than that of 5,10 and 20(P＜0.05).The activities of pyloric caeca protease and amylase were the highest when the salinity was 0.The protease activity of liver was very low,but the activities of liver amylase and lipase were the highest in each salinity.The activity of alkaline phosphatase was the highest when the salinity was 10 in intestinal tissue of young chum salmon.Stomach and intestinal protease activity of 30 days was higher than that of 130 days in young chum salmon.2.To fresh water for the control group,experiments were conducted to investigate the changes of haematological physiological and biochemical indexes in young chum salmon at different salinities.Five different salinities were set which were 0,5,10,15 and 20 respectively,the acute salinity experiments lasted for 130 days.The results showed that the effect of salinity on the number of erythrocyte,the content of hemoglobin and erythrocyte fragility is little,the highest values of erythrocyte number and hemoglobin content were at salinity 10,in 30 days,the most erythrocyte fragility of the erythrocyte was at salinity 20,and the youngest erythrocyte fragility was at salinity 5; in 130 days,the impact of salinity on the biochemical indexes were greater,serum osmolality and sodium was higher at salinity 15,20(P＜0.05);serum chlorine with an increase in salinity has increased significantly(P＜0.05);the content of serum potassium between different salinities and freshwater was significant difference(P＜0.05);the content of serum magnesium at salinity 20 was significantly higher than salinity 0 and 5(P＜0.05);the content of blood glucose was the highest at salinity 10,it was significant difference between salinity 10 and salinity 5,20 significantly(P＜0.05); the content of serum total protein,albumin,globulin was overall downward trend with an increase in salinity,the serum total bile acid,lactate dehydrogenase,alanine aminotransferase,blood urea nitrogen was significant difference between freshwater group and other salinity group(P＜0.05), aspartate aminotransferase was significant difference at salinity 0 and 15(P＜0.05).Through the measures of blood physiological and biochemical composition,the basis was provided in order to further understand the physiological and biochemical characteristics of chum salmon.3.With the technology of histology,to study the impact of salinity on the digestive tract and liver of young chum salmon,it carried out 130 days,two samples were collected and observed,at 30 days and 130 days respectively,the results show:the impact of salinity on stomach and liver of young chum salmon was great,the impact on intestine was small;at high salinity,the gastric cells were more,the boundaries between connective tissue and gastric epithelium was clear,and at low salinity (salinity 0,5),the gastric cells was less,the structure of connective tissue was irregular;at low salinity,some liver cells was breakdown,liver tissue was serious vacuolization;at high salinity,the number of goblet cells has increased on the anterior intestine,the density of intestinal villi also increased;the changes of hind intestine was not obvious with the histology observation.4.Study and investigate the survival and growth adaptation of young chum salmon in freshwater. The cultivation of chum salmon in freshwater was 10 months,the fish rearing density was adjusted appropriately in accordance with the size of fish;it was fed twice a day,feeding the volume of 3-6%(body weight).The average weight of young chum salmon was 179±5.5g at the end of the experiment.The growth and feeding of young chum salmon in freshwater was normal performance, but the death rate was about 30%in the period of young chum salmon silver film in fresh water;it was found that some fish were to appear deformity:body bending,eye swelling,and the rate of deformity was about 10%.At home and abroad,there was not the report about the cultivation of large-sizedchum salmon in freshwater,it was to provide experimental basis for rearing and research of young chum salmon in freshwater.To sum up,through the adaptation of young chun salmon in different salinity,it was found that the activities of digestive enzymes in young chum salmon were high at the high salinity;in salinity more than 10,the blood physiological and biochemical indicators of young chum salmon was in a better status,the physiological function of fish was normal basically;histology observation can be seen the structure of the normal histology at high salinity.So body of young chum salmon can be the capacity of adjustment in low-salinity water environment,they can be a normal growth in fresh water,but the results of some physiological and biochemical indicators and the histology of young chum salmon showed that it existed bigger difference between rearing in fresh water and in different salinity,it maybe cause the changes of pathologica tissues and organs for long-term live in freshwater,thus affect their growth and development,it was to be studied in depth. |
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