Effects Of L-malic Acid On Gastrointestinal Histology And Function,TCA Cycle Efficiency Of The Liver Of Gift Tilapia (Oreochromis Niloticus)

A detailed review of the advances in the nutrition of malic acid at home and abroad were first introduced in this thesis, and then the studies on nutritional physiology of malic acid in animals was undertaken. This study chose juvenile tilapia (Oreochromis niloticus) as experimental object to study the effect of dietary L-malic acid supplementation on gastrointestinal histology and function, TCA cycle efficiency of the liver in order to determine the appropriate level of L-malic acid for tilapia as well as to discuss the mechanism of L-malic acid on tilapia. And procide fundamental basis for the application of L-malic acid and acidifying agent in the tilapia feed, and also supply the important reference for the fish forage acidifier study in other fish.This experiment was conducted to study the effects of dietary L-malic acid levels on intestinal structure and function, and TCA cycle efficiency in liver of Gift tilapia. The experimental diets supplemented with0(control group),1.0,2.0,4.0,8.0,16.0and32.0g/kg L-malic acid had been fed to juvenile tilapias with initial body weight of (37.94±0.09) g for154days.420juvenile tilapias were randomly divided into seven groups of which each group had three replicates(20fishes for each replicate). During the experiment,21experimental rectangular glass tanks(active volume0.32m3) with the recirculation system were used in the experiment. The oxygen level was maintained above6mgO2/L.Water temperature was ranged from22to28℃,pH was6.5-7.0, and total ammonia-nitrogen was below0.05mg/L. After the breeding test, we researched the effects of L-malic acid on the gastrointestinal histology and function, TCA cycle efficiency of the liver of tilapia.The results are summarized as follows:(1) The effects of L-malic acid on the activity of pepsin and the ability of secreting acidWith increase in L-malic acid supplementation, pepsin activity was significantly increased(P<0.05) and the maximum value was in the32.0g/kg group. Compared with control group(without supplementation of LMC), it increased by115.71%. Except for the16.0g/kg group, H+-K+-ATPase activity of other groups was significantly lower than the control group(P<0.05).(2) The effects of L-malic acid on the content of gastric EGF and EGFR of tilapiaThe content of gastric EGF and EGFR showed an increasing and then decreasing trend with the increment of L-malic acid supplement, which were highest in8.0g/kg group and significantly higher than those in control group(P<0.05). Compared with control group, it increased by56.30%and56.30%respectively.(3) The effects of L-malic acid on histological structure of stomachThe gastric antrum appearance, determined from scanning electron microscopy(SEM), no sign of inflammation or damage were observed. But the cell boundary of mucosal epithelium in8.0g/kg group was more distinctive than the control group and the32.0g/kg group. Transmission electron microscopy(TEM) observations confirmed that in three groups the surface mucous epithelium displayed healthy, normal morphology with no signs of disease or cell damage. However in the32.0g/kg group, the glandular cells showed vacuolar degeneration,and the mitochondrion of a few glandular cells demonstrated vacuolization. The swollen nucleus were also observed in the32.0g/kg group.(4) The effects of dietary L-malic acid on intestinal digestive enzyme and Na+-K+-ATPase activity of tilapiaIntestinal amylase and lipase activities increase and then decreased, reaching the highest in1.0g/kg group, which was63.21%and37.22%higher than those in control group. The activity of lipase in2.0g/kg～32.0g/kg has no significant difference(P>0.05). The protease activity increased gradually with the increaseding the level of L-malic acid. The activity of Na+-K+-ATPase were highest in16.0g/kg group, which was74.54%higher than those in control group.(5) The effects of L-malic acid on the content of intestinal EGF and EGFR of tilapiaThe intestinal content of EGF and EGFR were increased gradually with the increaseding the level of L-malic acid (P<0.05). The content of EGF and EGFR were highest in16.0g/kg group, and were35.21%and58.73%higher than those in control group.(6) The effects of dietary L-malic acid on intestinal morphology of tilapiaWith the increment of L-malic acid supplement, the villus height, villus density and muscular thickness of foregut and midgut were highest in16.0g/kg group which were86.89%,41.94%,104.59%and115.42%,29.00%,19.40%higher than those in control group(P<0.05). The villus height, villus density and muscular thickness of hindgut gradually decreased (P<0.05), and were lowest in the32.0g/kg group.(7) The effects of dietary L-malic acid on CS and the content of ATP in hepatopancreas of tilapias With the increase of L-malic acid, citrate synthase activity was first increases and then decreased. And it reached the highest in8.0g/kg group,23.49%higher than the control group.The content of ATP were increased gradually with the increaseding the level of L-malic acid (P<0.05)This study indicated that in the dietary of Gift tilapia, a proper addition of L-malic acid(1.0-8.0g/kg) can improve the morphology of stomach, foregut and midgut, promote the proliferation of gastrointestinal mucosal epithelial cell, and improve the ability of gastrointestinal digestion and absorption, and the efficiency of liver TCA cycle.