| GIFT is the genetically Improved Farmed Tilapia Strain of nile tilapia(Oreochromis niloticus), which have became an important aquaculture species. Unbalance nutrition in diet, i.e. low protein, high fat, high carbohydrate, and vitamins lacking, lead to the liver damage, smaller body and poor quality of fish. Lipid is an important nutrient for fish and it is difficult to be replaced by other nutrients because of its unique biological function. In order to explore the optimal lipid demand and the regulation mechanism of different lipid levels on fat metabolism and key enzyme in lipid metabolism for GIFT tilapia, the optimal lipid demand of GIFT tilapia, and the effects of different lipid levels on fat deposition, fatty acid composition were studied; the GIFT tilapia fatty acid synthase (FAS), lipoprotein lipase (LPL) cDNA were first obtained; the effects of lipid levels and refeeding on the activity, expression of FAS and LPS and blood biochemical parameters were studied.1 Effects of dietary lipid levels on growth, muscle composition, feed apparent digestibility, muscle composition and blood biochemical parameters of GIFT strain of nile tilapia(Oreochromis niloticus)In order to determine the optimal levels of the lipid of GIFT Strain of Nile tilapia (Oreochromis niloticus),630 GIFTs (average weight 2.63±0.16 g) were divided into six groups randomly, with one control group that fed with basal diet (1.73%lipid) and five experimental groups fed with different lipid level diet (3.71%,5.69%,7.67%,9.64%and 16.55%) by supplementing with 2%,4%,6%,8%and 15%fish oil as lipid source, respectively. Every group was triplicate. After rearing for 90 d, the fish was fasted for 48 h, then three fishes were randomly selected from each group, and the growth, feed conversion ratio, muscle composition, digestive enzyme activities, nutrient apparent digestibility and blood biochemical parameters were detected. The results showed that, along with dietary lipid level raising, weight gain rate and specific growth rate had a trend of going up first then falling down, protein efficiency ratio improved (P<0.05) and feed conversion ratio reduced (P<0.05). Lipid content of muscle increased with increasing dietary lipid levels by the range of 2.29%to 4.27%, protein, ash and phosphorus contents had a decreasing trend. There was no significantly change of the protease activities of stomach and intestine between each treatments (p<0.05), however the lipase activities of foregut and midgut, and amylase activities of foregut were significantly decreased with increasing of dietary lipid levels (P<0.05). Second-order regression analysis of weight gain rate on dietary lipid level indicated that the optimal dietary lipid for maximal growth of GIFT was about 9.34%. Crude protein and dry-matter digestibility had no significant effect by dietary lipid levels (P>0.05). Crude lipid and phosphorus digestibility increased significantly with dietary lipid level increasing (P<0.05). Albumin and albumin/globulin ratio in 1.73%group (control group) was significantly higher than other groups (P<0.05). Along with dietary lipid level increasing, cholesterol and alkaline phosphatase of fish serum raised significantly (P<0.05). Dietary lipid level had significantly influence on blood glucose (P<0.05), and had no significantly influence on the content of triglyceride, activities of glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase (P>0.05). Those results indicated that a certain content of lipid in diet could promote the growth and improve the apparent digestibility of lipid and phosphorus, but excessive amount of lipid might be negative for fish growth and blood biochemical parameters. So, the optimal added levels of lipid in GIFT diet was 7.67%-9.34%.2 Effects of dietary lipid levels on fat deposition and fatty acid composition of GIFT strain of nile tilapia (Oreochromis niloticus)The conceptual design of raising was the same as that of the One. Raised for 90 d, the fish was fasted for 48 h, then three fishes were randomly selected from each group, and the effects of dietary lipid levels on partial physique indices, the fat deposition and fatty acid composition in muscle, liver and celiac adipose tissue of GIFT were studied. The results showed the condition factor in 5.69%,7.67%and 9.64%group was higher than other groups; the hepatosomatic index of 1.73%and 16.55%group were significantly higher than that of other groups (P<0.05). Except 1.73%group, the index of viscera-body in other groups were increased as increasing lipid level in diet. The fat content of muscle in 7.67%group were significantly higher than that of 3.71%group (p<0.05) and lower than that of 16.55%group (P<0.05). The higher of dietary lipid level, the fat deposition in fish body and the proportion of unsaturated fatty acids in total fatty acids were higher, accordingly. Those results different dietary lipid levels could affect the partial fish physique indices, especially on the hepatosomatic index. Excessive lipid in diet made lipid easier to be accumulated in muscle and liver, and the fat contents and fatty acid composition of fish could reflect the lipid level and fatty acid composition in diet.3 Molecular Cloning and sequence analysis of FAS and LPL from GIFT strain of nile tilapia(Oreochromis niloticus)The FAS and LPL cDNA sequences were cloned from GIFT (Oreochromis niloticus) by using RT-PCR and RACE method. The obtained partial FAS cDNA was 557 bp in length encoding 185-aa (GenBank accession no. GU433188). Sequence analysis showed that GIFT FAS shared 62%-82%identities with other species FAS. The full length of GIFT LPL cDNA was 2298 bp in length encoding 515 amino acids (GenBank accession no. GU433189). Sequence analysis showed that GIFT LPL shared highly identities with other vertebrates LPLs, ranging from 57.3%to 87.9%. The residues and motifs needed for LPL function was also conserved in GIFT. The predicted protein structure of GIFT LPL showed that it possessed the typical structure of lipase.4 Effects of dietary lipid levels and refeeding on the activity and expression of FAS in GIFT strain of nile tilapia(Oreochromis niloticus)To study the FAS activity and gene expression affected by different dietary lipid levels, 315 healthy fish (average weight 2.63±0.16 g) was divided into three groups and fed with different lipid levels (3.71%,7.67%and 16.55%). The low lipid level group (3.71%) was set as control group. After feeding for 90 d, the fish were fasted for 48 hours and then the activity and gene expression level of FAS in liver and muscle were studied; Furthermore, using realtime PCR analysis the FAS mRNA expression level in liver was examined at 6,12, 24,48 h after refeeding with different lipid level diet. The results showed that there was no significantly effect of dietary lipid level on FAS activity in liver (P>0.05); the expression level of FAS mRNA in liver was significantly higher than that in muscle (P<0.05). Meanwhile, the expression levels of FAS mRNA in liver and muscle were significantly decreased with rising of dietary lipid level (p<0.05). After refeeding for 6 to 48 h, the expression level of FAS mRNA in liver was significantly decreased in each group (P<0.05). Those results indicated that the higher dietary lipid level could not induce the secretion of FAS in liver; the expression level of FAS mRNA in liver was significantly higher than that of in muscle. The higher dietary lipid level could inhibit the expression of FAS mRNA, and the tendency is the higher of lipid level the more inhibition. The expression of FAS was also inhibited after refeeding.5 Effects of dietary lipid levels and refeeding on the activity and expression of LPL in GIFT strain of nile tilapia (Oreochromis niloticus)The conceptual design of raising was the same as that of the Four. Raised for 90 d, the fish were fasted for 48 hours and then the activity and gene expression level of FAS in liver and muscle were studied; Furthermore, using realtime PCR analysis the FAS mRNA expression level in liver was examined at 6,12,24,48 h after refeeding with different lipid level diet. The results showed that GIFT LPL also was detected in adult liver and muscle which was in accordance with other piscine LPL. However, the expression level in liver was significantly higher than that in the muscle (P<0.05). GIFT LPL expression was increased with the increasing of lipid level in diet, with the highest in 16.55%group and significantly higher than that of 3.71%group (P<0.05). Furthermore, expression level of GIFT LPL in liver was increased after fasting for 48 h, and decreased after refeeding for 12 h and then back to the level at beginning of fasting. Those results indicated that the higher dietary lipid level could induce the secretion of LPL in liver; the expression of GIFT LPL was in a tissue specific pattern and the GIFT liver was the main organ for secretion and expression of LPL. The higher lipid in diet induced the expression of LPL in liver and this condition was regulated by the feeding status (satiation or starvation).6 Effects of dietary lipid levels and refeeding on lipid and sugar in the blood of GIFT strain of nile tilapia(Oreochromis niloticus)To explore further study of the effects of dietary lipid level on the blood lipometabolism parameters, the blood was randomly collected from three fish in 3.71%, 7.67%and 16.55%group after fasting for 24 h and refeeding for 0,6,12,24,48 h, and the blood indices related to lipometabolism, i.e. blood glucose(GLU), triglyceride (TG), cholesterol (CHO), were detected. The results showed that the higher lipid in diet could significantly increase the TG, CHO, alkaline phosphatase (ALP) and glutamic-pyruvic transaminase (GPT) (P<0.05), and decrease blood sugar (P<0.05); After refeeding for 48 h, the TG, CHO and GLU were first increased and then decreased. At the same time-points after refeeding, the TG and CHO of the high-lipid group were significantly higher than that of the low-lipid group (P<0.05), the GLU had a decreasing trend but no significant change was observed (P>0.05). Those results indicated that the high-lipid level (16.55%) might be harmful to liver. After refeeding for 48h, the TG, CHO, GLU appeared to be a singlet curve and reached to the highest at 12 h,6 h and 12 h after feeding, respectively. The same case was also observed in high-lipid group and middle-lipid group. The high-lipid could reduce the metabolism of TG and make time of CHO lag to 12 h after feeding. |
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