| In recent years,the shrimp aquaculture industry has developed rapidly around the world,extending from the coast to inland areas.Intensive culture and environmental deterioration induce abnormal pigment,low immunity,high incidence and rough meat quality,which have seriously affected the nutritional quality and sales volume of shrimp products.In order to solve above problems,this study started with the shrimp food structure,and the effects were compared by supplementation with a gradient of Haematococcus and synthetic astaxanthin.It is widely used in nutrition science,cosmetics,food and aquaculture feed industries due to its powerful anti-oxidant properties,including colorants and antioxidants.According to the source of astaxanthin,it can be divided into natural and synthetic astaxanthin.Natural astaxanthin is mainly divided into Haematococcus pluvialis astaxanthin and Phaffia rhodozyma astaxanthin,due to the ratio of geometric isomers of Haematococcus pluvialis as well as the presence of predominant 3S,3'S enantiomer configuration,which is similar with the configuration of astaxanthin in aquatic animals.This experiment was conducted to investigate Haematococcus pluvialis astaxanthin.By analyzing the pigment content and configuration of diets and shrimp after ingestion,the exact endogenous mechanism of astaxanthin on the growth,immune response and disease resistance of shrimp was studied based on astaxanthin composition.Besides,try to understand the changes of astaxanthin configuration during the digestion,absorption and accumulation of shrimp.The main results in this study are as follows:1.To explore the effective carotenoid content contained in diets,the carotenoid contents in diets were determined,and the loss rate and retention rate of carotenoid during the production process were also obtained.Results showed that after high-temperature heating and extrusion during the material preparation,the Haematococcus diet maintained 39%carotenoid content,and chemosyntheyic astaxanthin diet retained 27.3%carotenoid content.Being stored in the dark at room temperature after 30 days,the Haematococcus diet kept 92%carotenoid content,and synthetic astaxanthin diet retained 61%of the carotenoid content.2.To study the differences of astaxanthin content and configuration(geometric and optical isomers)between Haematococcus pluvialis and synthetic astaxanthin diet,astaxanthin content and configuration in two diets were studied.Results showed that the ratio of 3S,3'S enantiomer:3R,3'S meso:3R,3'R enantiomer was30:3:1 in Haematococcus pluvialis diet,and the ratio of cis/trans isomer was 0.21.And the ratio of 3S,3'S enantiomer:3R,3'S meso:3R,3'R enantiomer was 6:2:1 in synthetic astaxanthin diet,and the ratio of cis/trans isomer was 0.13.3.To study the effects of different sources of astaxanthin on physiological and biochemical parameters of Litopenaeus vannamei,the study was conducted based on shrimp fed with 5 different carotenoid content diets(control,S-Ast70,N-Ast50,N-Ast90 and N-Ast140).Weight gain,length gain of shrimp and antioxidant enzyme activities in vivo(SOD,CAT and GPx)were measured.The results showed that plant-derived astaxanthin could significantly increase weight and length gain at the same of astaxanthin concentration.SOD and CAT activities showed a"low-high-low"pattern with increasing astaxanthin content,and the highest enzyme activity of CAT appeared in shrimp of N-Ast140.4.To understand the effects of different sources of astaxanthin on the carotenoid content and configuration of shrimp,our study investigated carotenoid content,astaxanthin content and configuration in shrimp to explore carotenoid digestion and absorption and cumulative metabolic pathways.The results showed that there was no significant difference in the carotenoid content between the experimental groups fed with astaxanthin(P>0.05),and the astaxanthin content in shrimp accumulated with the increasing astaxanthin content in diets.The cis/trans isomer ratio of shrimp in the N-Ast140 group was 0.191,and there was no significant difference among the other groups.The ratio of optical isomers in shrimp was 5:4:1 to 3:3:1,which was extremely different from the ratio of optical isomers in diets.Therefore,we concluded that an epimerase may exist in the astaxanthin metabolic pathway in juvenile shrimp.5.To understand the effect of different sources of astaxanthin on the shrimp anti-stress ability,our study determined the survival rate of shrimp under dry exposure after 45 min and 21°C in sea water-7°C 10 min-21°C in sea water.The results showed that astaxanthin could increase the dehydration time of shrimp and maintain a certain survival rate.The survival rates of shrimp in N-Ast90 and N-Ast140 groups were significantly higher than that in N-Ast50 and S-Ast70(P<0.05).After 10 min at low temperature,the survival rate of shrimp in N-Ast140group was highest after 1 h.6.To explore the effects of different sources of astaxanthin on the shrimp disease resistance,Vibrio parahaemolyticus was added into water of L.vannamei for 72 h and the bacterial density was maintained at 3×10~8 cfu/m L.The results showed that shrimp in N-Ast140 and N-Ast90 groups were superior to shrimp in other groups.After challenge,the mRNA expression of cMnSOD in N-Ast90 group was significantly increased(P<0.05),and the GPx mRNA expression in the S-Ast70 group was significantly reduced(P<0.05).The above data shows that the stability of natural astaxanthin is better than synthetic astaxanthin under high and normal temperature.Haematococcus diet has a higher cis/trans isomer ratio and 3S,3'S enantiomer content,and its antioxidant activity is better,and it is more easily digested and accumulated in shrimp.The results show that the optimum amount of natural astaxanthin in Litopenaeus vannamei juveniles is 90 mg/kg,which can significantly increase the activity of antioxidant enzymes,the survival rate of shrimp under stress and the gene expression of antioxidant enzymes after challenge.These provide a theoretical basis and data support for common problems that arise in shrimp aquaculture. |
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