الفهرس 
ACKNOWLEDGEMENT
Phytase: mode of actionOnly 14 pages are availabe for public view
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Abstract
This study was carried at the experimental fish farm, poultry production Department, Faculty of Agriculture, Assiut University, Egypt. This experiment was designed to study the effect of addition microbial phytase on growth performance of Nile tilapia (Oreochromis niloticus).To study the physiological effects of microbial phytase on Nile tilapia (Oreochromis niloticus). This experiment was designed to study the effect of microbial phytase on growth performance, some blood constituents and carcass composition in Nile tilapia (Oreochromis niloticus). Healthy, Nile tilapia (Oreochromis niloticus) with an average initial body weight of (13±1g) was used in this experiment. The fish were obtained from the experimental fish farm belonging to the Department of Poultry Production, Faculty of Agriculture, Assiut University. The experimental fish were adapted for two weeks in cylindrical tanks (1.5m diameter X 2m depth). All experimental fish were fed on basal diet three times daily at a rate of 3% live body weight. At the end of adaptation period, a total number of 600 healthy fish were individually chosen, weighed and measured for the total length, then distributed randomly on six experimental groups (100 fish each) as follow:
1- The first group was fed on the basal and considered as a control
diet.
2- The second group was fed on the basal diet supplemented with
500 units of commercial phytase/kg diet (T2).
3- The third group was fed on the basal diet supplemented with
750 units of commercial phytase/kg diet (T3).
4- The fourth group was fed on the basal diet supplemented with
1000 units of commercial phytase/kg diet (T4).
5- The fifth group was fed on the basal diet supplemented with 1250 units of commercial phytase/kg diet (T5).
6-The sixth group was fed on the basal diet supplemented with
1500 units of commercial phytase/kg diet (T6).
During the experimental period (12 weeks), fish weight and length were measured individually every two weeks. The quantity of food was re-adjusted biweekly according to the live body weight (3%). Feed was provided three times/day (9:00 AM ; 12:00 PM and 3:00 PM).
The temperature in water had been measured three times daily (8:00 A.M, 12:00 noon, and 5:00 P.M) throughout the experimental period (12 weeks). At the end of study 20 fish of each treatment were taken to estimate both body weight and body length. HSI, SSI and GSI were calculated individually. The chemical analyses of fish muscles (moisture - dry matter - crude protein - crude lipid and crude ash) for each treatment were estimated. The blood samples were taken individually for the measurement of hemoglobin, total protein, albumin, globulin and glucose.
The obtained results showed that:
1- Growth performance:
a- The average body weight at the end of the experiment indicated that the fourth group had a superior body weight as compared to the control and other groups without any significant effect.
b- The average body weight gain at the end of the experiment indicated that the fourth group had a superior body weight gain as compared with the control group.
c- The average specific growth rate at the end of the experiment showed that the fourth group had the highest specific growth rate as compared to the control group.
d- The average body length at the end of the experiment indicated that the second, third, fourth and fifth groups increased without any significant effect as compared to the control group.
e- The average body length increment at the end of the experiment showed that the fourth group had the highest length increment as compared to the control group.
f- The average condition factor (K-value) at the end of the experiment cleared that the second group had the highest condition factor as compared with the control group. While, the averages of condition factor didn’t show any significant effect.
2- Hepato, spleeno and gonado – somatic indices:
The average hepatosomatic index (HSI) for the control, second, third, fifth and sixth groups significantly (P<0.05) decreased while, the fourth group insignificantly (P>0.05) increased. While, the averages of spleeno-somatic index (SSI) of there groups showed insignificantly (P>0.05) differences except the second, third, fourth and fifth groups were significantly (P<0.05) different than the control group, while the sixth group showed lower values than the other groups. Also, the average gonado-somatic index for male (mGSI) decreased for the first, fourth, and fifth group, while the third group significantly (P<0.05) increased as compared with the control group, while the second group had insignificant (P>0.05) increase. The average gonado-somatic index for female (fGSI) insignificantly (P>0.05) increased in all groups as compared to the control group.
3- Blood components:
The hemoglobin (Hb) level was increased significantly (P<0.05) for all groups. While, the sixth group significantly (P<0.05) decreased as compared to the control group.
The serum total protein increased significantly (P<0.05) in the fourth group. While, the second, third, fifth and sixth groups insignificantly (P>0.05) increased as compared to the control group.
Also, the serum albumin levels increased significantly (P<0.05) for the fourth, fifth and sixth groups as compared to the control. While the second and third groups showed insignificantly (P>0.05) increase as compared to the control group. Moreover, there were significant (P<0.05) increase in serum globulin for the second, third and fifth groups significantly (P<0.05) increased as compared to the control group. While, the fourth group insignificantly (P>0.05) increase as compared to the control group. Also, serum glucose of the treated groups increased significantly (P<0.05) as compared to the control group.
4- Chemical analysis of muscle composition of O. niloticus:
There were insignificant (P>0.05) differences in moisture, dry matter and crude protein of fish groups fed different levels of dietary phytase as compared to the control group. The decrease of crude protein for the treated fish groups may be due to the decrease of serum total protein. The supplementation with dietary phytase for the fourth and fifth groups led to significant (P<0.05) decrease the fat content of O. niloticus. Moreover, the second and third groups showed significant (P>0.05) increase as compared to control group. While, the averages of ash content for fish fed phytase increased significantly (P<0.05) in the second, third, fourth, fifth and sixth groups as compared to the control group.
Moreover, it could be summarized that the principle effects of microbial phytase on O. niloticus.
1- Insignificant (P>0.05) improvement in body weight, body weight gain,
specific growth rate, body length, length increment and condition factor for the fish groups fed diet supplemented with microbial phytase.
2- Insignificant (P>0.05) improvement in hepato-somatic index, spleeno-somatic index and gonado-somatic index for male while, significant (P<0.05) improvement in gonado-somatic index for female the fish groups fed diet supplemented with microbial phytase.
3- The hemoglobin level was significantly (P<0.05) higher for all groups except the fifth group.
4- Total protein increased significantly (P<0.05) in the fourth group. While, serum albumin increased significantly (P<0.05) for the fourth, group. While, serum globulin for second group significantly (P<0.05) increased. Also, serum glucose increased significantly (P<0.05) in all fish groups (T3, T4,T5 and T6) fed dietary phytase as compared to the control group.
5- The crude protein, moisture and dry matter insignificant (P>0.05) differences were in fish groups. While, the crude fat was significantly (P<0.05) decreased in the fourth and fifth groups.
6 The ash content was increased significantly (P<0.05) in all groups as compared to the control group.