| Sturgeons belong to Phylum Chordata (chordates), the Class Osteichthyes, Subclass Actinopterygii and they are often the largest and the oldest freshwater fishes in the world. Russian sturgeon(Acipenser gueldenstaedtii), one of the 27 species of Acipenseriformes, was introduced into China since 1990s and has became one of the most important commercial fishes in China due to its fast growth and high nutritional value. However, the information about nutrition, especially lipid nutrition, of Russian sturgeon is urgently needed because of high hepatic lipid content caused low anti-stress and high morality was increased in recent years, and also the increasing interest from commercial farms in producing meat and caviar. This paper focuses on the Russian sturgeon larval hepatic lipid content and lipid metabolism regulation from the following several aspects in order to develop the most efficient and healthy commercial feed.:1) the lipid contents and lipid metabolism of Russian sturgeon’s liver, subcutaneous tissue and muscle,2) the effect of different dietary lipid source on growth performance, whole fish lipid composition, hepatic lipid content and lipid metabolism of juvenile Russian sturgeons,3) the effects of dietary lipid level and n-3/n-6 fatty acid ratio on growth, fatty acid composition, and lipid peroxidation in Russian sturgeon Aciepnser guldenstaedtii,4) the effects of dietary vitamin E, betaine, L-carnitine and taurine on growth performance, lipid contents and hepatic lipid metabolism of juvenile Russian sturgeon. The main results and conclusions were as follows:1. The lipid content and lipid metabolism of Russian sturgeon’s liver, subcutaneous tissue and muscleThe aim of this study was to investigate the lipid content and lipid metabolism of three important tissues in lipid metabolism:liver, subcutaneous tissue and muscle. The lipid content of the three tissues revealed that subcutaneous tissue and liver might be the main lipid deposition tissue in Russian sturgeon, whose lipid content were 30.77 ± 3.29% and 24.64±3.95%, respectively. Whereas, the lipid content of muscle was only 5.32±0.58%. The related expression of lipogenic genes (sterol regulatory element binding protein-1c, acetyl coenzyme A carboxylase a and fatty acid synthase) were highly expressed in liver, while fatty acid beta oxidation-related genes (acyl-CoA oxidase a, carnitine palmitoyl transterase-lA and carnitine palmitoyl transterase-1B) were highly expressed in subcutaneous tissue. The three iso-type peroxisome proliferator activated receptor (PPARa, PPARβ and PPARy) were all highly expressed in liver. The related expression of hormone sensitive lipase and lipoprotein lipase were high in subcutaneous tissue. The results showed that subcutaneous tissue might be the main lipid deposition tissue of Russian sturgeon, and liver was the main lipogenic tissue.According to the results above and server high hepatic lipid content in farming Russian sturgeon, this study was focused on hepatic lipid deposition of Russian sturgeon and disscuss the character of hepatic lipid deposition in Russian sturgeon. The present study was designed to investigate the effects of dietary lipid sources, lipid level and n-3/n-6 ratio, vitamin E, taurine, L-carnitine and taurine on growth performance and hepatic lipid deposition of Russian sturgeon, the hepatic lipid metabolism regulation was also determined by molecular biology techniques.2. Growth, fatty acid composition and lipid deposition of Russian sturgeon fed different lipid sourcesThe growth performance, fatty acid composition and lipid deposition in Russian sturgeon (initial body weight:1.80 ± 0.09 g) were investigated by using diets containing three different lipid sources:fish oil (FO), sunflower oil (SO) and linseed oil (LO) for eight weeks. The weight gain of sturgeon fed linseed oil was significantly lower than that fed with SO. The fatty acid composition of the whole body was influenced by the fatty acid profile of the diet. The level of malondialdehyde in serum significantly increased in fish fed with FO and LO. The hepatosomatic index and viscerosomatic index were significantly decreased in the LO group. Lipid contents in the muscle and liver were also significantly decreased in the fish fed linseed oil. The relative expression of hepatic lipogenesis related genes (PPARγ、ACC and FASN) were not affected by dietary lipid sources, but the relative expression of lipolysis related genes (PPARa and ACOa) were significantly decreased in dietary linseed oil group. The results above suggested that the growth, fatty acid composition and lipid deposition of Russian sturgeon were affected by lipid source, and the more suitable lipid source to replace fish oil was sunflower oil, not linseed oil.3. Effects of dietary lipid level and n-3/n-6 fatty acid ratio on growth, fatty acid composition, and lipid peroxidation in Russian sturgeonThe growth performance, fatty acid composition, hepatic lipid content, hepatic somatic index, and lipid peroxidation in Russian sturgeon were investigated by using diets containing three lipid levels 5%(L5),15%(L15) and 25%(L25) and three n-3/n-6 fatty acid ratios (1:3,1:1 and 3:1) for eight weeks. Weight gain significantly increased with the increase of dietary lipid levels at the n-3/n-6 fatty acid ratios of 1:3 and 1:1, but not at the 3.1 ratio. Correspondingly, fish survival gradually decreased with the increase of dietary lipid at the 3:1 n-3/n-6 fatty acid ratio. The dietary lipid level significantly affected the composition of whole body fatty acid. The retention of highly unsaturated fatty acid dramatically decreased at the level of 25% dietary lipid. The liver malondialdehyde increased with the increase of dietary lipid levels and the n-3/n-6 fatty acid ratios. The contents of lipid and triglyceride in the liver, and the hepatic somatic index also increased with the increase of dietary lipid. The diet combination of L25+ 3:1 showed the highest aspartate transaminase and alanine transaminase, indicatives of hepatic injury. This study indicated that the L25+1:3 diet can improve fish growth performance whereas the L25+3:1 diet may lead to poor growth performance due to high lipid peroxidation.4. Effects of dietary vitamin E, betaine, L-carnitine and taurine on growth performance, antioxidation activity and lipid deposition of Russian sturgeonHigh lipid content and high n-3/n-6 ratio can increase hepatic lipid content and cause liver damage. Therefore high lipid and high n-3/n-6 ratio diet may cause liver damage of Russian sturgeon, which can be used as a model to investigate the lipotropic angets on growth performance, antioxidation activity and lipid deposition of Russian sturgeon. This study was designed to examine the effects of dietary vitamin E, betaine, L-cartine and taurine on growth performance, antioxidation activity and lipid content of juvenile Russian sturgeon by using five iso-energy, iso-protein diets:control diet, 200 mg kg"1 vitamin E,1000 mg kg-1 betaine,1000 mg kg-1 L-carnitine and 1000 mg kg-1 taurine. Weight gain was significantly increased by dietary taurine and L-cartine compared to control group, and the weight gian were 239.05 ± 6.87% and 214.23 ± 8.38%, respectively. The serum malondialdehyde content, the hepatic somatic index and the lipid contents in liver and muscle were not affected by vitamin E, betaine, L-cartine or taurine. Therefore, the four lipotropic agents used in this study had no influence on muscle or hepatic lipid content, but did increase the growth of Russian sturgeon. It was unknown that whether the dose of lipotropic agent applied in this study was not adequate, therefore, more investigation were necessary to be conducted in the future.5. Effect of dietary L-carnitine on growth, antioxidation activity, lipid content and hepatic lipid metabolism of Russian sturgeon Acipenser gueldenstaedtiiL-carnitine plays a critical role in fatty acid catabolism by directing fatty acids into the mitochondrial oxidative pathway through the action of specialized acyltransferases. In aquaculture and poultry industry, L-carnitine has a multi functional purpose:growth promotion, antioxidant effects, reducing fat content, protein sparing and strengthening the immune system. So in the present study, six iso-protein and iso-energy diets containing different dietary L-carnitine levels:0,250,500,250,500 and 4000 mg kg-1 were made to investigate the effects of L-carnitine on growth performance, antioxidation activity, and hepatic lipid metabolism of juvenile Russian sturgeon. Weight gain increased with dietary L-carnitine level and reached the highest weight gain at 500 mg kg-1 L-carnitien group, and then it decreased with dietary L-carnitine level when L-carnitine>500 mg kg-1. The feed conversation ratio had an opposite trend with wight gain. The serum malondialdehyde content, the muscle and liver lipid content, the hepatic somatic index were not affected by dietary L-carnitine level. The hepatic lipolysis and lipogenesis-related genes were not affected by dietary L-carnitine either. But 500 mg kg-1 L-carnitine significantly increased hepatic lipoprotein lipase and hormone sensitive lipase relative expression. In conclusion, dietary L-carnitine can enhance growth performance of Russian sturgeon, but had no effect on lipid content of muscle and liver.In summary, Russian sturgeon is one of the chondrostean fish, which is between chondrichtyan and teleost on the evolution. The lipid metabolism might be different from other fish species, and this provides us with important clues to understand the evolution of the metabolism organization of the vertebrates. In this study, liver was the main lipid deposition tissue, and played important role in lipid metabolism of juvenile Russian sturgone. Dietary linseed oil, containing high 18:3n-3, decreased hepatic lipid content which might because of lipolysis related genes promoting effects, but it also dereased growth performance of Russian sturgeon, therefore, sunflower oil might be the suitable lipid sources to replace fish oil, not linseed oil; the gowth performance and hepatic lipid content increased with dietary lipid levels in the background of 1:3 and 1:1 fatty acid ratios, but high dietary lipid level and high n-3/n-6 ratio might cause liver damage because of high lipid content and high lipid peroxidation level. High lipid and high n-3/n-6 ratio diets caused liver damage can be used as a model to investigate the sutible lipotropic agents of Russian sturgeon. However, the hepatic lipid content and lipid metabolism were not affected by the four lipotropic agents selected in this sturdy (vitamin E, betaine, L-carnitine and taurine), but they did increased the growth performance of Russian sturgeon. So, high lipid level and high n-3/n-6 ratio was not recommend in practical diet formulation. |
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