| This study was carried out to investigate the mechanism of dietary protein and amino acids in digestion, absorption and utilization in all-male yellow catfish, to acquire optimum requirements of dietary protein and lysine for this fish. For these objectives, all-male yellow catfish were used through several experiments such as growth trials, digestive test and comparative slaughter trials in combination with analyzing growth performance, digestive enzyme activities as well as gene expressions to improve parameters in nutritional physiology and nutrient demands of all-male yellow catfish. The main findings were as follows:1. Three formulated diets with different protein levels(40 %;37 %;34 %) fed all-male yellow catfish with average body weight 10.11±0.12 g were conducted to investigate the effect of apparent digestibility and the activities of digestive enzyme.Results showed:1)Dietary proteins had impact significance determination (P<0.05) on the apparent digestibility of energy, crude protein, fat and amino acids, and presented a rising trend with the decreasing of protein levels;2) The intestines amylase and pepsin values were similar among treatments(P>0.05), except other activities of digestive enzyme(P<0.01); high levels of lipase and pepsin activities in different tissues were recorded in 37% protein diet; the trypsin activity in each treatments decreased with decreasing of protein levels. In conclusion, appropriately reducing protein content of feed, can significantly improve thedigestibility of nutrients and increase the amylase, lipase and pepsin activities of all-male yellow catfish.2. Five diets with different protein levels (43 %;42 %;40 %;39 %;36 %) were formulated to feed all-male yellow catfish with average body weight 2 g for 60 days, which were conducted to investigate the effects on growth performance and plasma biochemical index of all-male yellow catfish. Results indicated:1)weight gain rate, specific growth rate and protein efficiency rate at 42% protein diet was the highest (P<0.01),and feed coefficient at 42% protein diet was the lowest (P<0.01),and using PER as a reference index we could calculate the optimum dietary protein level of all-male yellow catfish was 41.77%; 2)With the decreasing of dietary protein levels, the retention efficiency of CP,EE and Ash had an increasing tendency among groups (P<0.01);3)Dietary proteins had impact significance determination(P<0.05) on ALT and AST,but TP,ALB,GLOB,GLU,BUN,CHO1 and TG were similar among treatments(P>0.05);4)The protein content of whole body, muscle and viscera-dislodged had no significant difference in each group (P>0.05);The fat content of whole fish increased with the protein levels decreasing (P<0.01), while the fat content of muscle reduced with the with the protein levels decreasing (P<0.01), and the fat content of viscera-dislodged in each group were significantly different (P<0.05);The ash content of whole body and viscera-dislodged decreased with the decreasing of protein levels(P<0.01), while the ash content of muscle increased with the decreasing of protein levels(P<0.01);With the decreasing of protein levels, the amino acids content of whole body had no significant difference in each group(P<0.05), while the total amino acids content and the total essential amino acids content of muscle and viscera-dislodged had shown a decreasing trend among groups (P<0.05 or P<0.01).In conclusion, the feed of all-male yellow catfish optimum protein content is 41.77% under the experimental conditions of the present study.3. A study was undertaken to research the the growth performance and the nutrient digestibility of all-male yellow catfish.For that purpose 4 diets were formulated to be isonitrogenous(38%, CP) to feed all-male yellow catfish with average body weight 9.29±0.11 g. The experimental diets were supplemented with 1.4% microencapsulation lysine(?),0.7% microencapsulation threonine(?), and 0.37% methionine(?) on the base of control diet(I). The results showed that:1)weight gain rate and protein efficiency rate in ? were significantly higher than the other three groups(P<0.05), and the feed coefficient is significantly lower than other groups(P<0.05), but there had no significant difference among ?,control group and ?(P>0.05).Survival rate found no significant difference among groups(P>0.05).2)The digestibility of dry matter, crude protein digestibility had no significant difference between ? and IV (P>0.05), but they were significantly higher than control group and ? (P<0.05);The digestibility of fat in IV was the highest(P<0.05);The energy digestibility in ? was significantly higher than the other three groups (P<0.05);The digestibility of amino acids in ? was the highest(P<0.01),while in control group was the lowest(P<0.01), except for the digestibility of glutamic acid (P>0.05).In conclusion, supplemented with 1.40% microencapsulation lysine in the compound feed(38%, CP) has obvious growth-promoting effect to all-male yellow catfish.4. Nine diets were formulated to be isonitrogenous(34%,CP) to feed all-male yellow catfish with average body weight 5.5 g for 63 d, which were conducted to investigate the utilization effects of adding crystalline or microencapsulation lysine into feed and the suitable lysine requirements for all-male yellow catfish. The experimental diets were supplemented with 0.5 %,1.5 %,2.5 % crystalline lysine (?,?,?) and 1.0 %,2.0 %,3.0 %,4.0 %,5.0% microencapsulation lysine (?,?,?,?,?) on the base of control diet(I).The results indicated:1)with the increasing of lysine level, weight gain rate, specific growth rate, protein efficiency rate appeared in the trend of first increased then decreased (P<0.01), and using PER as a reference index we could calculate the optimum dietary lysine level of all-male yellow catfish was 2.61 %;2)The deposition rate of protein,fat,ash and amino acids had an increasing trend in crystalline lysine groups(P<0.05), and a reducing trend in microencapsulation lysine groups(P<0.05);3)The protein content had no significant difference among groups, but the fat content increased with the rising of lysine level(P<0.05) which contrary to the ash content(P<0.05);3)With the increasing of lysine level, the amino acids content of whole fish had no obvious change (P>0.05),but the amino acids content of muscle presented a decreasing trend and viscera-dislodged appeared in the trend of first increased then decreased(P<0.05).In conclusion, the feed of all-male yellow catfish optimum lysine content is 2.61% under the experimental conditions of the present study, and adding crystalline or microencapsulation lysine to the low protein feed (34%) can promote the growth of all-male yellow catfish.5. The tissue distribution and the effects of adding crystalline or microencapsulation lysine of y+LAT1 mRNA in all-male yellow catfish were analyzed using RT-PCR and real-time PCR.The results showed that:1) y+LAT1 mRNA was detected in 9 tissues, and its expression patterns among the tissues were in order:pylorus>liver>brain, heart,stomach,foregut,midgut> kidney>hindgut,significantly(P<0.05);2)The expression of y+LATl mRNA in foregut and stomach showed a increasing trend when adding micro capsule lysine in the feed.In conclusion,adding micro capsule lysine in the feed could induce upregulation the expression of y+LAT1 mRNA in foregut and stomach. |
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