Effects Of Haematococcus Pluvialis On The Growth And Antibacterial Properties Of Litopenaeus Vannamei

Litopenaeus vannamei is one of the three largest economic aquaculture shrimps in the world.It preys on algae and other plankton in natural waters,and thus contains astaxanthin in the body,which promotes the growth performance,reproduction and disease resistance of shrimp.Vibrio parahaemolyticus,the main pathogen of acute hepatopancreatic necrosis(AHPND)in shrimp.The affected shrimp showed lethargy,slow growth,soft-shells,an empty stomach and midgut,and pale to white atrophied hepatopancreas and necrosis that caused juvenile shrimp death.Studies have indicated that astaxanthin can enhance the antioxidant capacity of shrimp and tolerance under low salinity,high temperature,and low dissolved oxygen stresses,and improve the resistance of juvenile shrimp to various pathogenic bacteria.Haematococcus pluvialis is a unicellular green alga rich in astaxanthin,which is known as a natural"super antioxidant".At present,H.pluvialis is mainly used as medicines,health foods,and colorant for precious seafood such as salmon.If apply H.pluvialis as a feed additive can improve the growth performance and resistance to bacterial infection of L.vannamei?This is the key question that our study intends to solve.In this study,the effects of H.pluvialis on growth performance and antibacterial ability of L.vannamei were studied by adding different contents of H.pluvialis to the shrimp feed,and further to determine the potential application value of H.pluvialis in the pilot culture of L.vannamei.The specific results are as follows:1. Use a double screw extruder to make shrimp feeds containing 0%,1%,3%,5%,and7%H. pluvialis dry powder.The effects of this microalgae on growth,nutritional value and antibacterial effect of L.vannamei were studied for four weeks feeding trail in 50 L barrel.The results showed that the feed conversion ratio of the experimental group showed a downward trend with the increase of the content of algal powder,and the 3%,5%,and 7%groups had significant differences in contrast to control group(P<0.05),and the feed effect was better.2. The content of astaxanthin and vitamin E in the tissues of the experimental group of shrimps increased gradually with raising of the algal content,and the 7%group was the highest content.In the fourth week,the astaxanthin content in the muscular tissue was 3.45times than the control group,the astaxanthin content in the shrimp shell was 5.28 times of the control group,and vitamin E in the muscle tissue was 8.97 times of that in the control group,and the astaxanthin content gradually ascending according to the feeding time.3. After 42 hours of infecting with V. parahaemolyticus,the survival rate of the shrimp in the experimental group showed increase initially and then decreased,and there was a significant difference between the 1%,3%,5%groups and the control with 7%groups(P<0.01).The survival rate of the 3%group reached 60%was the highest.The relative expression of the immune related gene Lv Toll,the T-SOD enzymatic activity and MDA content reflecting the antioxidant activity of the shrimp after Vibrio challenge are similar to those of the survival rate of the shrimp.In 1%and 3%group,the relative expression levels of Lv Toll gene were significantly reduced(P<0.05),and T-SOD activity and MDA content were significantly decreased(P<0.05).Therefore,H.pluvialis can significantly improve the growth performance and disease resistance of L.vannamei.4. In order to apply H.pluvialis in pilot-scale culturing of L.vannamei,and considering the cost accounting of industrialized shrimp feeds,the amount of H.pluvialis was reduced by1 0 times,in this way to detect the effects of low content of H.pluvialis on the growth and disease resistance of L.vannamei.Shrimp feeds containing 0‰and 3‰H.pluvialis were prepared with double screw extruder.L.vannamei was reared in a 15 m~3concrete pond for 45days.The results showed that the content of linoleic acid and EPA in the fatty acids of the3‰group in the shrimp tissue was significantly higher than that in the control group.The proportion of essential amino acids in the shrimp of the 3‰group was closer to the human body,with higher nutritional value.In terms of economic benefits,the weight of the final harvested shrimp increased significantly(P<0.05),which can bring certain economic benefits.The results of this study fully show that H.pluvialis can promote the growth and disease resistance of L.vannamei,increase its nutritional value,and increase the economic benefits of shrimp farming.The results provide important theoretical and practical basis for the large-scale application of H.pluvialis in aquaculture.