Effects Of Rearing Density And Feeding Strategies On Growth,Feed Utilization And Anti-stress Ability Of Juveniles Megalobrama Pellegrini

In this study,the effects of rearing density on growth,antioxidant enzymes activities and stress-related genes expression of juveniles Megalobrama pellegrini were studied.In addition,the effects of feeding frequency and feeding level on the growth,body composition and digestive enzymes activities of juveniles Megalobrama pellegrini were investigated.The experimental results are as follows:1.Effects of rearing density on growth,body composition,antioxidant enzymes activities and stress-related genes expression of juveniles Megalobrama pellegriniFive density treatments groups 0.01kg/m~3,0.24kg/m~3,0.34kg/m~3,0.42kg/m~3and0.50kg/m~3(50,80,110,140 and 170 tails/tank)were set up in the experiment.Triplicated groups were set up and the experiment was carried out for a period of 42 days.Experiment results showed that the average final weight,weight gain and specific growth rate of juveniles Megalobrama pellegrini increased first and then decreased with the increasing of density.The maximum value appeared in 0.34kg/m~3groups.There was no significant difference between groups in weight gain and specific growth rate.The feed coefficient rate showed the opposite trend which was decreasing first and then increasing with the increasing of density.The survival rate of each group was high and there was no significant difference.The whole-body moisture in the 0.34kg/m~3group was significantly higher than that in other density groups.The activity of superoxide dismutase(SOD)in the intestinal tract of juveniles Megalobrama pellegrini of the 0.50kg/m~3group was significantly lower than that of other groups,and malondialdehyde(MDA)content began to decrease and then increased.The glutathione(GSH)content of the 0.34kg/m~3group was significantly higher than those of other density groups.The total antioxidant capacity(T-AOC)activity of the0.24kg/m~3group was significantly higher than that of other density groups.The expression levels of cytochrome oxidasegene(CYP1A)and medullary differentiation factor(Myd88)genes in intestinal tract of juveniles Megalobrama pellegrini were maximized in 0.50kg/m~3group.The expression levels of heat shock protein 90(HSP90)and nuclear factor KB inhibitor(IKBa)genes were not significantly affected by the rearing density.The Mn superoxide dismutase(Mn-SOD)gene expression level was the lowest in the highest density group.The expression level of nuclear factor E2 correlation factor 2(Nrf2)gene in intestinal tract of juveniles Megalobrama pellegrini with the highest rearing density was significantly higher than that of the lowest density group.Nuclear factor kβ(NF-kβ)gene expression was highest in 0.42kg/m~3group.2.Effects of feeding frequency and feeding level on growth,body composition and digestive enzymes activities of juveniles Megalobrama pellegriniThe experiment designed 2 feeding frequencies(2 times a day,3 times a day)and 3feeding levels(5%,6.5%,8%),named as 2-5,3-5,2-6.5,3-6.5,2-8,3-8,respectively.Three parallel feeding levels were set for each treatment group,and the experiment was carried out for 42 days.Experiment results showed that growth performance of 2 times/day feeding frequency group was significantly different from that of 3 times/day feeding frequency group.The growth performance at feeding frequency of 2 times/day was significantly different from that at 3 times/day.The final mean weight and weight gain rate of juveniles Megalobrama pellegrini were significantly higher in group 2-6.5 than in group2-5.When feeding frequency was 3 times/day,the specific growth rate of juveniles Megalobrama pellegrini was significantly lower in group 3-6.5 than in group 3-5.The feed coefficient in group 3-8 was significantly lower than that in group 2-5.The survival rate of2-8 groups was almost zero.In addition,the crude fat,crude protein and moisture of the3-8 group were significantly lower than those of the 2-5 group.When the feeding level was unchanged,the crude fat and crude protein content decreased significantly with the increase of feeding frequency,and the highest value appeared in group 2-5.The highest values of lipase,alpha-amylase,trypsin and alkaline phosphatase in the intestinal tract of juveniles Megalobrama pellegrini were found in group 3-5.Intestinal lipase and amylase of juveniles Megalobrama pellegrini were significantly decreased in group 3-8 compared with group 2-5.