| In order to provide tequnical supports to establish a high density and high quality cultivation technology for rotifers Brachionus plicatilis,and to apply rotifers into the nursery period for shrimp post larvae,commercial astaxanthin was added to microalgae Nannochlorsis sp.solution to feed rotifers,and effects of different concentrations of astaxanthin on the rotifer’s population growth,bioaccumulation rates and related water quality were analyzed.Post larvae(PL5)of the Pacific white shrimp Litopenaeus vannamei were fed with the astaxanthin enriched rotifers,and the growth performance,body color,antioxidant and hypoxia tolerant abilities were investigated..The details were as follows :1.Effects of astaxanthin on population growth,bioaccumulation and water quality of rotifers.The culturing tank was 120 L with a water temperature at 23-26 ℃ and salinity at18 ‰.The microalgae liquid was used as the control group(group D),where 0.05 mg/L(group A),0.10 mg/L(group B)and 0.15 mg/L(group C)astaxanthin were added to continuously culture rotifers for 7 days.The results showed that rotifer density in group C(134±9)ind./mL was significantly higher than that in group B(122±6)ind./mL(P<0.05),and extremely significantly higher than that in group D(90±3)ind./mL and group A(111±5)ind./mL(P<0.05).The average daily growth,average daily growth rate and final growth multiple were the highest,which were(17.1±1.3)ind./mL,(36.6± 1.0)% and(13.0±0.9)times,respectively.The astaxanthin content in rotifers in groups A,B and C was always higher than that in group D at all time points,and the difference was significant(P<0.05).The contents of astaxanthin in rotifers of group D and group A reached the peak at 6h,which were(2.37±0.2)μg/g and(12.54±1.3)μg/g respectively.The astaxanthin content in rotifers of group B and group C reached the highest at 4 h,which was(17.02±1.6)μg/g and(19.46±1.1)μg/g,respectively,with significant difference(P<0.05).The enrichment efficiency of astaxanthin in each group was the highest at 2 h,and the enrichment efficiencies of astaxanthin in group A,B and C were(2.82±0.31),(4.63±0.54)and(5.43±0.47)μg/(g·h),respectively,which were significantly higher than those in group D(0.29±0.06)μg/(g·h)(P<0.05).The concentration of ammonia nitrogen in the culture water of group C was the highest(2.4±0.2 mg/L)and was significantly higher than that in group A and group D(P<0.05).The changes of nitrite and pH in the culture water of rotifers in each group were relatively stable and there was no indigenous difference;the dissolved oxygen content in each group was negatively correlated with rotifer density,and the dissolved oxygen content in group C was significantly lower than that in other groups(P<0.05).2.Effects of astaxanthin supplementation on growth and body color of Litopenaeus vannamei larvae.Different astaxanthin concentrations(0.05,0.10,0.15,0 mg/L,respectively)were used to strengthen rotifers(group A,B,C and D)with artificial compound feed to feed P5 larvae,and group E was the control group.The feeding experiment lasted for 28 days.The results showed that the survival rate of larvae in group B(85.2%)was the highest,significantly higher than that in group D(79.2%)and group E(72.8%)(P< 0.05),The final body length,final body weight,weight gain rate and specific growth rate of group C were the highest,which were(4.5±0.2)cm,(1.2±0.1)g,(540.7±45.4)% and(4.4±0.2)%,respectively.The astaxanthin content in group B(4.58±0.43)μg/g was slightly higher than that in group C(4.36±0.47)μg/g(P>0.05),significantly higher than that in group A(3.47±0.43)μg/g,group D(1.98±0.21)μg/g and group E(1.25±0.15)μg/g(P< 0.05).3.Effect of astaxanthin supplementation on antioxidant enzyme activity and intestinal flora structure of Litopenaeus vannamei larvae.Method as described in 2.The results showed that T-AOC and CAT activities of hepatopancreas in group B were significantly higher than those in other groups(P<0.01).The SOD activity of hepatopancreas in group A was significantly higher than that in other groups(P< 0.05).There was no significant difference in the number of intestinal flora OTU and species richness(ACE,chao1)among the groups(P>0.05).At the phylum level,the relative abundance of Proteobacteria in the intestine of larvae first increased and then decreased with the increase of astaxanthin addition,and there was no significant difference between groups A(73.72±3.27)%,B(63.75 ± 4.68)% and D(66.54 ± 5.12)%(P>0.05).Group C(54.46 ± 3.42)% was significantly lower than other groups(P<0.05).The relative abundance of Bacteroidetes also increased with the increase of astaxanthin addition.The relative abundance of Bacteroidetes in group C(42.25±3.21)% was significantly higher than that in other groups(P<0.05),There was no significant difference among groups A,B and D(P>0.05).which were(23.35±2.12)%,(33.27±1.61)% and(24.40±1.72)%,respectively.4.Effects of astaxanthin supplementation on low salt tolerance of Litopenaeus vannamei larvae.Salinity Sudden Drop Stress Test Based on Experiment 2 and 3,The results showed that there was no significant difference in the activities of T-AOC and SOD in hepatopancreas of larvae in groups A,B and C under salinity stress(P>0.05).T-AOC in group D and E was significantly decreased(P<0.05),while SOD and CAT activities were significantly increased(P<0.05).When the salinity dropped sharply to 10‰,the survival rates of larvae in group B and group C were the highest(88.3±1.3)%,which were not significantly different from those in group A(86.7±0.7)%(P>0.05),but significantly higher than those in group D(83.3±0.7)% and group E(85.0±0.7)%(P< 0.05).When the salinity dropped to 2‰,the survival rate of larvae in group B was the highest(86.7±1.3)%,and that in group D was the lowest(81.7±1.3)%,with significant difference(P<0.05). |
