| 1.Study on the transfer of nitrogen in the algal-Daphnia magna systemFive Microcysis aeruginosa-D.magna systems were designed with different N/P ration and constant P content(N0(4:1),N1(8:1),N2(16:1),N3(20:1),N4(24:1)),in which the content of total nitrogen(TN),nitrate nitrogen,nitrite nitrogen and ammonia nitrogen was determined,aiming to explore the transfer of nitrogen in the water.The results showed that the feeding behavior of D.magna inhibited the growth of Microcysis aeruginosa,and inhibition decreased with the increase of algae density.There was no significant difference on number of D.magna between day1 and day2 in the N0 group,and significant differences were found at other times.In the N1 group,there was also no significant difference in the number of D.magna in the 1st,2nd and 4th day.Compared with the two groups above,the growth trend of D.magna in the group N2 and N3 was delayed,and the number of D.magna increased after the 7th day,and the significant difference was appeared in group N1 on the 14 th day.There were significant differences in the measured values of each time node in group N4.When the density of M.aeruginosa in the N4 group reached 1.36*107cell/ml,all the D.magna died.With the increase of nitrogen content in each experimental group,the content of nitrogen in the algae increased,so in the D.magna.There was a trend of decrease in TN and nitrite nitrogen in each group,but the purification effect was not obvious.The nitrate content in each group increased and followed by decrease with time,and the nitrate nitrogen content increased the fastest in the N4 group,and the lowest was in the N0 group.For N0,N1,N2 and N3,independent sample t-test results showed that there were significant differences only between N0 and N3 groups.The ammonia nitrogen content of all five groups showed a trend of decline as time changes;for N0,N1,N2 and N3,independent sample t-test results showed significant difference was found only between the groups of N2 and N3(P<0.05).The results indicated that in the Algae-Daphnia systems with different nitrogen and phosphorus ratios,algae could use ammonia nitrogen in water as the nitrogen source for survival;at the same time,different forms of nitrogen were converted to each other,and the converted nitrogen content increased with the increase of n/p ratio when there was suitable algae density.2.The effect of Daphnia magna on the concentration of suspended solids and N in sewageDaphnia magna is able to feed suspended solids and can affect the content of nitrogen nutrient salts in water.In thisexperiment,the effect of D.magna on the content of suspended particles in urban sewage in 15 days was discussed,and the nutrient in water was measured.Obtained experimental results showed that with the extension of time,the density of the D.magna was gradually increased,reaching the highest peak(238 inds/l)on the day12.The content of suspended particles in the control group was fluctuating,and the fluctuation trend of group S1 and group S0 was similar.In the first four days of the experiment,with the density of D.magna in S1 group from low to high,the content of suspended particles in S1 group fluctuated greatly,reached the highest(79.5 mg/l)in the day4.The content of suspended matter decreased in the 5th to 10 th day,and the minimum value appeared on the day10 of 45.25mg/l.At the post period of the experiment(days6-10),the TN content of group S1 was lower than that of S0 group,and the removal effect of TN was not obvious compared with S0.In the early stage of the experiment(day1-6),with the increase of D.magna,ammonia nitrogen was decreased first and then increased,and in the 9th day,ammonia nitrogen content in the water was the highest(39.61 mg/l),far higher than the control group.The nitrate content in the S0 group showed the fluctuation trend and reached the lowest value on day 6.The content of nitrate nitrogen was higher during the experiment process compared to initial value,and the maximum value appeared in day 11(42.54 mg/l).The variation trend of nitrite nitrogen content in S0 group and S1 group was similar,the highest value of S0 group was 20.91mg/l,and the maximum value of S1 group was 26.46mg/l.The independent sample T test was conducted for S0 and S1 group,and the results showed that there was no significant difference except day9 between the two groups in the three-form nitrogen content in the water(P<0.05).The experimental results indicated that the D.magna could survive in the urban sewage containing suspended particles,and the low density of D.magna could promote the reduction of TN content.3.Nutrient analysis and potential utilization value of Daphnia magna used as aqua-feed feedstockA trail was conducted to determine nutrient composition and heavy metal content of dried Daphnia magna from artificial-cultivation pond in spring,summer,autumn,winter and eutrophic lake sewage in summer,aiming to assess potential utilization value in aqua-feed.The results showed that there was significant seasonal difference on the moisture of artificial cultivated D.magna,the highest was 5.14% in winner,and the lowest was 2.51% in summer(P<0.05).The moisture content(9.12%)of D.magna in summer sewage was significantly higher than that of artificial cultivation.The content of protein of artificial cultivated D.magna was 30.93%-50.21% with significant differences in different seasons(P<0.05),and in winter and summer sewage was significantly higher than that of other groups.The total content of 15 amino acids determined markedly differed among groups,with the highest(36.65%)in winter and the lowest in summer(24.74%).In summer sewage,the amino acid content was 41.79%,and 9 essential amino acids accounted for 22.15%,Lysine content reached 3.4 %,Methionine 1.14 %,and Threonine 2.45 %.The fat content was also significantly different with seasonal variation(P<0.05),the highest fat content was observed in winter(18.88%),while the lowest in autumn(4.19%),and no significant difference on the fat content was found in winter and summer sewage.The essential fatty acids were the highest in autumn and the summer sewage(17%),and the arachidonic acid and linolenic acid were not detected in all samples.The highest levels of heavy metal chromium,copper,zinc and lead appeared in summer sewage and artificial-cultivation pond in autumn,spring and summer,respectively,and no lead was detected in summer sewage and winter,no cadmium in all groups.Except for chromium,the lowest concentrations of copper,lead,arsenic and zinc were found in the summer sewage.All the results indicated that the D.magna was rich in protein and fat with lower potential toxicity of heavy metals,both the essential amino acid and essential fatty acid nutrient value in summer sewage were generally higher than those of artificial cultivation,so it is more feasible to use the D.magna in summer sewage as the feed protein source.4.Effects of replacement of fishmeal by Daphnia magna on growth performance,body composition and hepatopancreas function of Macrobrachium rosenbergiiDaphnia magna,as one of the common zooplankton species in eutrophic water,has high nutritional value,thus its utilization draws more attraction.In order to make full use of them to protect environment and lessen aquafeeds to rely on fish meal,this experiment was conducted to investigate the effects on growth,muscle composition,hepatopancreas function and immune-related genes of Macrobrachium rosenbergii when the dietary fish meal was partly replaced with dried D.magna.The experimental basic diet(D0)containing 30% fish meal was substituted with 5%(D5),10%(D10),15%(D15)and 20%(D20)of dried D.magna respectively,at approximate isonitrogenous and isoenergetic level.The results showed that,no significantly different specific growth rate(SGR)of M.rosenbergii was found between D10 and D0 group,while remarkable difference of SGR between D5,D15,D20 and D0.The survival rate of each replacement group was significantly higher than that in the D0 group and the maximum value was in D15 group;the feed conversion radio(FCR)was firstly decreased and then increased and the highest value was found in D5group;the crude protein,crude fat and water content of Macrobrachium rosenbergii decreased and then increased,the highest values were observed in D15 D0 and D0 groups respectively.The content of ash in muscle of D15 group was significantly higher than that in other groups(P<0.05).There was no significant difference in apparent digestibility of dry matter between the groups.The activities of superoxide dismutase(SOD)in hepatopancreas were firstly decreased and then increased with increasing inclusive D.magna,and the lowest was in D10.The content of malondialdehyde in hepatopancreas was significantly higher in D10 than that in other groups(P<0.05),with the lowest content in D20.The malondialdehyde content in serum were significantly lower in the replacement groups than the D0 group(P<0.05);the activity of aspartate transaminase(AST)in each alternative group was less than the D0 group;the activity of glutamic-pyruvic transaminase(GPT)in serum was no significant difference between D0 and D5,but significantly higher than other groups(P<0.05).The activity of alkaline phosphatase(AKP)was fluctuant among groups(P<0.05)The results showed that there were no significant differences on Tollm RNA and NFKBm RNA expression levels in the gill among all groups.The HSP70 expression in hepatopancreas appeared an increasing trend with the increasing of D.magna with no significant difference among the groups..All the test results indicated that the addition of 10% couldn't lead to decreased growth performance,and inclusion 10%~15% of the dried D.magna replacing isonitrogenous fish meal could improve digestibility and muscle protein nutritional value.The partial replacement of fish meal by no more than 20% of dried D.magna caused different levels of stress and was beneficial to the health of the hepatopancreas of Macrobrachium rosenbergii.There was no obvious link between these effects and the expression of Tollm RNA and NFKBm RNA.5.Effects of Substituting Fishmeal with D.magna on intestinal microorganisms in Macrobrachium rosenbergiiThe nutrient level of the feed can affect the intestinal microorganisms of aquatic animals,but there is little research on the intestinal flora of Macrobrachium rosenbergii.In this experiment,three groups of feed D0,D10 and D20 were prepared by using the addition of 0%,10% and 15% of the Daphnia magna,which were used to replace the fishmeal with isonitrogen in the feed.The results showed that there was no significant difference in the expression of Ace and Chao in D0 and D20,and D10 was significantly higher in Ace and Chao than D0 and group D20.The value of Shannon index is D0<D20<D10,and there was no significant difference among the three groups.Simpson index was D0>D10>D20,also no significant difference among the three groups.Proteobacteria were dominant in the intestinal microorganism of M.rosenbergii,accounting for about 50%.The second dominant bacteria group was Tenericutes,which accounted for about 25%.With the content of D.magna increased and fishmeal decreased in the feed,the structure of intestinal flora changed.The dominant genus was opportunistic pathogen Aeromonas in group A,and with the increase of D.magna,the dominance of the Aeromonas in the population decreased,and D0(33.80%)> BD10(17.48%)>D20(3.61%).The Lactococcu increased in proportion(6.61%),and the proportion of candidatus-hepatoplasma was D10(25.91%)>D0(25.94%)> D20(22.48%).Therefore,it can be concluded that the substitution of D.magna for fish meal in the feed of M.rosenbergii resulted in more complicated intestinal microorganism was.A decrease in the abundance of Aeromonas may reduce the risk that Macrobrachium rosenbergii will be infected by a pathogenic bacterium in water due to environmental changes.Similarly,an increase in the genus Lactococcus may cause reduced survival of M.rosenbergii. |
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