Study On Requirement And Utilization Of Juvenile Amur Sturgeon (Acipenser Schrenckii) For Some Dietary Nutrients

Amur sturgeon, Acipenser schrenckii, is one of the 27 existing Acipenseriformes species and a large riverine species native to Amur River, and has become the most popular sturgeon species for aquaculture in China because of its rapid growth, tasty quality and relatively few problems with diseases. So far, some studies were conducted on the lipid and protein requirement and evaluation of some lipid sources for Amur sturgeon. However, little information is available on the requirements and utilizations of the fish for dietary nutrients. Hence, the present study was conducted to investigate dietary requirements of phosphorus, vitamin A, vitamin E, and vitamin C and evaluate the effects of different carbohydrate, lipid sources and conjugated linoleic acid on growth and physiological performance for juvenile sturgeon. The contents are as follows:1. Dietary phosphorus requirement of juvenile Acipenser schrenckiiSix experimental isonitrogenous and isoenergetic purified diets were formulated containing increasing contents of phosphorus (0.18%, 0.40%, 0.71%, 0.98%, 1.38% and 1.66%, respectively). Monocalcium phosphate was used as dietary phosphorus source, casein and glutin as protein source, dextrin as carbohydrate source, and soybean oil and maize oil as lipid source, respectively. Each experimental diet was fed to triplicate groups of 20 Amur sturgeon juveniles with initial weight approximately 4.7g in 400-1 aquaria and maintained at 25.6±2.0℃for 8 weeks. The results showed that the weight gain rate, feed efficiency and specific growth rate of the juveniles increased significantly with the increasing of the dietary phosphorus level (P<0.05). These values reached the peak when the juveniles were fed the diet supplemented with 0.98% phosphorus, and then decreased significantly with the further increases of the dietary phosphorus level (P<0.05). The survival rate of the fish fed the control diet (0.18% phosphorus diet) was significantly lower than that of the fish fed the other diets (P<0.05). Supplementation of dietary phosphorus had no significant effect on the muscle moisture, crude protein, or crude lipid content of the juveniles (P>0.05). The fish fed the diets supplemented with 0.71%-1.66% dietary phosphorus had significantly higher ash, calcium, and phosphorus contents in vertebra than those fed the control diet and the 0.40% phosphorus diet (P<0.05). Broken-line regression analyses of specific growth rate and vertebrae phosphorus against dietary phosphorus level indicated that the dietary phosphorus requirement for optimal growth and phosphorus content in vertebra of juvenile Amur sturgeon was 0.88%-1.00% of dry diet.2. Dietary vitamin A requirement of juvenile Acipenser schrenckiiThe experiment was conducted to determine the dietary vitamin A requirement of juvenile Amur sturgeon by formulating seven semipurified diets containing 10, 258, 510, 1050, 2020, 4100 and 8300 IU vitamin A (as retinol acetate) kg^-1 diet, respectively. Each experimental diet was fed to triplicate groups of 20 early juveniles with initial average weight 12.09±0.22g in 405-1 aquaria and maintained at 25.0±2.0℃for 8 weeks. Fish fed the basal diet (10 IU vitamin A kg^-1 diet) exhibited bad appetite and activity, whereas these signs were not observed in any group fed diets supplemented with vitamin A. Weight gain, feed efficiency and hepatosomatic index increased significantly with the increases of dietary vitamin A level, which reached the peak at vitamin A 1050 IU kg^-1 diet, and then decreased. The muscle chemical compositions were not affected by dietary vitamin A levels. Vitamin A concentrations in liver and muscle increased significantly as vitamin A levels increased within a range of 10-4100 IU kg^-1 diet and above this, didn't change significantly. The activities of lysozyme activities and super oxide dismutase (SOD) in serum were the highest when the content of vitamin A was 1050 IU kg"1 diet. Either deficit or excess (>1050 IU kg^-1) of vitamin A in the diet would reduce the activities of the two enzymes. Broken-line regression analysis of weight gain against dietary vitamin A level showed that juvenile Amur sturgeon required a minimum of 923 IU vitamin A kg^-1 diet for maximal growth.3. Dietary vitamin E requirement of juvenile Acipenser schrenckiiThe effects of dietary vitamin E (dl-α-tocopheryl acetate) on growth performance and tissue vitamin E content of juvenile Amur sturgeon had been investigated. Triplicate groups of experimental fish with initial body weight (10.10±0.31)g were cultured and fed by semi-purified diets with seven levels of vitamin E supplements (0, 20, 50, 100, 200, 500 and 1000 mg/kg diet) at 10.46% dietary lipid for 8 weeks. The weight gain, feed efficiency, specific growth rate, survival rate and condition factor significantly (.P<0.05) increased concomitantly with increasing of supplemented vitamin E level and reached their peaks on the group fed with 200mg vitamin E/kg diet, respectively. With the further increase of supplemented vitamin E level, the weight gain, feed efficiency and condition factor significantly (P<0.05) decreased, whereas the specific growth rate had no significant (P>0.05) differences among treatments. Hepatosomatic index of the control group was significantly (P<0.05) higher than that of the other treated groups. The vitamin E content in liver and muscle significantly (P<0.05) increased concomitantly with increasing of supplemented vitamin E level. No significant (P>0.05) changes were found on vitamin E content in liver of groups fed with > 100 mg vitamin E/kg diets and on that in muscle of groups fed with≥200 mg vitamin E/kg diets. The crude lipid content in muscle of the control group was significantly (P<0.05) higher than that of the other treated groups, and the crude protein content in muscle of groups fed with >100mg vitamin E/kg diets were significantly (P<0.05) higher than that of the control group. The broken-line regression analysis of specific growth rates against dietary vitamin E levels suggested that the vitamin E requirement of juvenile Acipenser schrendkii for optimal growth might be 187.4 mg/kg diet.4. Dietary vitamin C requirement of juvenile Acipenser schrenckiAn 8 weeks growth experiment was conducted to determine the effects of dietary vitamin C on survival, growth, tissue ascorbic acid content, activity of serum lysozyme and serum cortisol concentration of Amur sturgeon with initial weight of 7.25±0.33g. Eight practical diets were formulated to contain 0.1, 58.2, 110.4, 221.8, 350.2, 475.6, 698.4 and 906.2 mg ascorbic acid equivalent kg-1 diet, supplied as enveloped ascorbic acid. Each diet was fed to triplicate groups of fish in aquarium, and each aquarium was stocked with 10 fish. Fish were fed four times daily to apparent satiation for 8 weeks. The water temperature fluctuated from 19.5 to 25.5 during the experimental period. The results showed that: No gross deficiency signs were observed in any of experimental fish. Survival rate was not significantly affected by the dietary vitamin C (P>0.05). Weight gain rate (from 514.46 to 680.31%), special growth rate (from 3.24 to 3.67 % day-1) and feed conversion ratio (from 0.85 to 0.70) were significantly affected by the dietary vitamin C (P<0.05). The vitamin C contents in liver and muscle positively correlated with the vitamin C in diets. The activities of serum lysozyme significantly increased with increasing dietary vitamin C, while the serum cortisol content significantly decreased. The Broken-line regression analysis showed the breakpoints were at 110.4 mg kg-1 based on maximal special growth rate, 279.4mg kg-1 on liver maximum storage of ascorbic acid.5. Effects of different carbohydrate sources on growth, some physiological and biochemical indexes of juvenile Acipenser schrenckiJuvenile Amur sturgeon were fed with 7 groups of isonitrogenous and isoenergetic diets containing 22% glucose, fructose, maltose, sucrose, dextrin,α-starch and corn starch respectively, for 8w to study the effects of differents dietary carbohydrate sources on growth, plasma glucose, liver glycogen concentration and the amylase activity of alimentary tract of juvenile Amur sturgeon. Each group had 3 replicates, and one replicate contained 20 fish (mean weight, 4.70±0.08g). The results showed: Weight gain rate (WG), specific growth rate (SGR) and feed efficiency (FE) of sturgeon were significantly (P < 0.05) affected by the different dietary carbohydrate sources. The effect of different dietary carbohydrate sources on the WG was dextrin,α-starch > glucose, corn starch > maltose > sucrose, fructose; SGR and FE had similar show to WG. Digestibility of sturgeon was significantly (P<0.05) affected by feeding different carbohydrate sources, on carbohydrate digestibility was glucose, fructose > maltose > dextrin >α-starch > corn starch; on protein digestibility was fructose > glucose, maltose, dextrin > corn starch >α-starch. Moisture, crude ash and crude lipid of muscle of sturgeon were significantly (P < 0.05) affected by the different dietary carbohydrate sources, but crude protein had no significantly difference (P>0.05). Plasma glucose and liver glycogen concentration of sturgeon were significantly (P<0.05) affected by the different dietary carbohydrate sources in different period after satiation. In different period after satiation, in stomach, amylase activity increased first and then decreased; in duodenum, the activity droped at first, then performed as same as in stomach; in intestinal valve, the activity increased at first then decreased, and performed again; the amylase activity of alimentary tract was significantly (P<0.05) affected by feeding different carbohydrate sources. In liver, no amylase activity had been detected. According to WG and SGR, the appropriate carbohydrate in diet of Amur sturgeon was dextrin andα-starch. 6. Effects of dietary lipids on the performance of growth, serum lipids and tissue fatty acid composition of juvenile Acipenser schrenckiAn 8-week growth experiment was conducted to test seven lipids on juvenile Amur sturgeon. The fish (initial body weight 9.83 g) in triplicate groups were fed with 10 % of each lipid included into basic diet in fiberglass tanks. Seven dietary lipids were fish oil, sunflower oil, tallow, lard oil, colza oil, corn oil and soybean oil repectively. The results showed that: The weight gain rate of fish fed soybean oil diet was the highest (611.29%) and group of sunflower oil was the lowest (451.57%) which were significantly lower than other groups. The lowest feed efficiency was also observed at group of sunflower oil which had significant difference from the other 6 groups. Fish fed with fish oil had the lowest condition factor and gut somatic index which were significantly lower than those of the other groups (P<0.05).There was no significant difference in hepatopancreas somatic index of the fish. The concentrations of cholesterol, triglyceride and low density lipoprotein cholesterol in serum of group fish oil and soybean oil were comparatively low in the 7 groups. The ratios of total n-3 polyunsaturated fatty acids in lipid of muscle of fish fed fish oil were significantly higher than those of fish fed other lipids (P<0.05), while the highest and the lowest ratios of total n-6 polyunsaturated fatty acids were observed in the fish fed soybean oil and fish oil, respectively. Compared comprehensively, the best dietary lipid to juvenile Amur sturgeon was soybean oil, the next in order was fish oil, while sunflower oil was minimal.7. Study on effects of conjugated linoleic acid on weight losing and lipid lowering of juvenile Acipenser schrenckiThe experiment was conducted to investigate the effects of dietary conjugated linoleic acid (CLA) on growth, body lipid level and serum lipids in juvenile Amur sturgeon. Groups of fish were fed controlled and enriched diets for 6 weeks to gaint high-lipid groups. Then, juvenile Amur sturgeons were randomly divided into control group and high-lipid +CLA groups (0, 0.5, 1.0, 2.0% CLA/control diet respectively). At the end of experiment, SGR decreased significantly by 1.0% and 2.0% CLA supplement (P<0.05). CLA had no effect on survival rate and FCR; CLA addition reduced condition factor among treatments. No differences were detected in body moisture, protein, and HSI, The lipid contents in liver reduced at 2.0% CLA feeding; TC decreased in serum when the fish were fed 1.0% and 2.0% CLA, and HDL-C decreased when supplied with 2.0% CLA, while, TG and LDL-C were silimar among treatments. In conclusion, the fortified CLA was effective in lowering growth, body lipid and blood lipids of juvenile Amur sturgeon, and the maximum effect on these appeared at the 2.0% CLA supplemented group.