| Determining feeding frequency and feeding level is an important part of shrimp culture management process in China,which can affect shrimp feeding activities.Excessive feeding level can also affect water quality and adversely affect shrimp health.In this study,Litopenaeus vannamei and Macrobrachium rosenbergii were used as research objects to explore the effects of feeding frequency and feeding level on their growth,digestion and immune function.The main results are as follows:(1)Study on growth performance:Litopenaeus vannamei and Macrobrachium rosenbergii were used as experimental shrimp.Four feeding frequencies and three feeding levels(2.0%,4.0%and 6.0% body weight for Litopenaeus vannamei and 1.5%,3.0% and 4.5% body weight for Macrobrachium rosenbergii)were designed for 30 days,respectively.The results were as follows: feeding frequency and feeding level significantly affected the growth rate of body mass,specific growth rate and survival rate of Litopenaeus vannamei and Macrobrachium rosenbergii.For Litopenaeus vannamei,when feeding frequency is 4 times /d and 5 times /d,feeding level is 4.0% and 6.0%,the growth is good,for Macrobrachium rosenbergii,when feeding frequency is 3 times /d and 4times /d,feeding level is 3.0%-4.5%,the growth is good.Feeding frequency had no significant effect on hepatopancreas index of Macrobrachium rosenbergii and Litopenaeus vannamei,feeding level had no significant effect on hepatopancreas index of Macrobrachium rosenbergii,but had significant effect on hepatopancreas index of Macrobrachium rosenbergii.(2)Study on microstructure of hepatopancreasThe histological structure of hepatopancreas of Litopenaeus vannamei and Macrobrachium rosenbergii was analyzed.The results showed that low feeding level had different effects on the histological structure of hepatopancreas of Litopenaeus vannamei and Macrobrachium rosenbergii.For Litopenaeus vannamei,at 2.0%feeding level,hepatic corbules were scattered,stellate lumen was deformed,secretory cells and storage cells were few,basement membrane was blurred,cell volume was larger,and hepatopancreas were damaged compared with those at 4.0% and 6.0%feeding level.For Macrobrachium rosenbergii,tissue sections showed hepatopantras were damaged at the 1.5% feeding level.(3)Study on hepatopancreas digestive function and antioxidant capacity:The activities of digestive enzymes and antioxidant enzymes in hepatopancreas of Litopenaeus vannamei and Macrobrachium rosenbergii were determined and analyzed.The results showed that: Feeding frequency and feeding level on shore,Litopenaeus vannamei and Macrobrachium rosenbergii of trypsin activity effect was not significant,but has a significant effect on lipase and amylase activity,according to think in a certain range increase feeding frequency and feeding level,to improve two shrimp digestive enzymes activity so as to promote the absorption of nutrients utilization;Feeding frequency had no significant effect on T-SOD activity of Litopenaeus vannamei,but had significant effect on T-SOD activity of Macrobrachium rosenbergii.Feeding frequency and feeding level had significant effect on CAT and GSH-Px activity of Litopenaeus vannamei and Macrobrachium rosenbergii.The antioxidant enzyme activities of Litopenaeus vannamei and P.rosenbergii in 4.0% and 3.0% feeding level groups were significantly higher than those in other feeding level groups;The results showed that after culture experiment,the immune level of Litopenaeus vannamei in 2.0% and 6.0% feeding level groups and Macrobrachium rosenbergii in 1.5% and 4.5% feeding level groups had decreased,and increasing feeding frequency could not effectively improve the immune level of Litopenaeus vannamei.(4)Study on expression of hepatopancreas growth and immune-related genes:The relative expression levels of growth and immune genes in hepatopancreas of Litopenaeus vannamei and Macrobrachium rosenbergii were analyzed.The results showed that: For Litopenaeus vannamei,feeding frequency had no significant effect on the relative expression levels of HK and ALP,but had significant effect on the relative expression levels of PK and ACP.Feeding level had significant effect on the relative expression levels of HK,PK and ACP,but had no significant effect on the relative expression levels of ALP.For Macrobrachium rosenbergii,feeding frequency had no significant effect on the relative expression levels of EcR and ALP,but had significant effect on the relative expression levels of PK and Chitinase.Feeding level had no significant effect on the relative expression levels of Ec R and ALP,but had significant effect on Chitinase and ACP.The results showed that,for Litopenaeus vannamei,increasing the feeding frequency and feeding level in a certain range could enhance the energy consumption of steady-state and foraging by enhancing the glycolysis process,and the level of non-specific immunity could be significantly increased.For Macrobrachium rosenbergii,at 2.0% feeding level,Macrobrachium rosenbergii inhibited the molting process by consuming its own energy for survival.In a certain range,the increase of feeding frequency promoted the expression of molting related genes and thus promoted the growth of Macrobrachium rosenbergii. |
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