| Pelteobagrus fulvidraco is a major farmed economic fish that is popular for its tender flesh.The growing number of farmers farming yellow catfishhas led to an increasing demand for juvenile yellow catfish.however,inappropriatehandling during transport can cause damage to its organism,and the survival rate of farming will be reduced,so the transport of juvenile fish is essential.The dorsal fins of juvenile yellow catfish arehard and prone to poking each other,especially athigh densities.And transporting farmed fish under stress can cause a series of changes in the physiological and biochemical responses of the fish.There are various ways to relieve adult fish transport stress,while fry are smaller,weaker and more sensitive to stress,so there are stricter requirements on the way to relieve stress.Research on the mitigation of transport stress in juvenile fish is still immature.In this study,the effect of transport density on the physiological,biochemical and genetic effects of different densities on the blood and liver of juvenile Pelteobagrus fulvidraco was investigated,and the stress relief of the blood and liver of juvenile fish was studied by adding encapsulated retardant,and the degree of stress relief of different retardant additions on the blood and liver of juvenile fish.The effect of the addition of three additives(Astragalus polysaccharide APS,Chitosan COS and Xylo-oligosaccharide XOS)on the alleviation of transport stress and the abundance of intestinal flora was also investigated to provide data to support the transportation of juvenile Pelteobagrus fulvidraco athigh densities and long distances to reduce transport costs.1.Effect of density stress on the physiological,biochemical,and immunological parameters of juvenile Pelteobagrus fulvidraco during live transportThe fish were designated to five density groups:D34,D12,D13,D14 and D15,with mass ratios of 1:1,1:2,1:3,1:4 and 1:5,respectively.Biochemical and immune function indices were subsequently evaluated.The total ammonia nitrogen level in the water increased with transport duration.After 36 h of transport,only the D15 grouphad a 100%survival rate,followed by D14 with 83%survival,and 0%in the remaining three density groups.The gill filament NKA(Na~+/K~+-ATPase)activity of the fish post-transport was significantly lower than that observed pre-transport(p<0.05)across all groups.The levels of serum glucose and cortisol were elevated with increasing density and transport time and were significantlyhigher in the density groups than those of the control group(p<0.05).Superoxide dismutase activity in liver tissues was significantlyhigher in the density groups than that in the control groups,whereas malondialdehyde and catalase levels reached a maximum and subsequently decreased.Lysozyme values peaked at 16 h and 24 h of transport in the D34 and D12 groups,respectively.The damage on gill filaments and the liver worsened with increasing environmental stress severity.The expression ofheat shock proteins 70 and 90(hsp70andhsp90,respectively),tumour necrosis factor-alpha(TNF-α),and interleukin-1 beta(IL-1β)in juvenile livers was significantlyhigher than that in the control group(p<0.05),confirming that density imposed stress on fish during transport.In conclusion,we demonstrated that increased density and time during live transport induced significant physiological stress responses in juvenile P.fulvidraco.The stress and damage caused to fish during transport athigh densities was confirmed.2.Effectiveness and effects of various complex retardants on the retardation of juvenile Pelteobagrus fulvidraco under transport stressSix inclusions of different substances at different concentrations EU-5 mg/β-CD(5 mg of clove essential oil was embedded withβ-cyclodextrin),EU-10 mg/β-CD(10 mg of clove essential oil was embedded withβ-cyclodextrin),VC-20 mg/β-CD(β-cyclodextrin was embedded with 20 mg of VC),VC-50 mg/β-CD(β-cyclodextrin was embedded with 50 mg of VC),EU-10 mg+VC-50 mg/β-CD andβ-CD(β-cyclodextrin was embedded with 10 mg of clove essential oil and 50 mg of VC),respectively were added to the transported water and used to alleviate the stress caused by transport to juvenile Pelteobagrus fulvidraco.The results showed that the total ammonia nitrogen level in the transport water added with EU-10mg+VC-50 mg/β-CD was significantly lower than that in the control group(p<0.05),and its survival rate was also thehighest,at 95%.The nexthighest survival rate was 93%for the EU-10 mg/β-CD group.The levels of serum glucose and cortisol in juvenile yellow catfish increased with increasing transport time and were significantly lower in each experimental group than in the control group(p<0.05).Among the liver oxidative stress indicators,the levels of both SOD and CAT increased with time,while thehighest level was reached in the VC-50 mg/β-CD group after 4h of transport.MDA levels in all groups decreased and then increased at the beginning of transport,except for the VC-50 mg/β-CD andβ-CD groups,where MDA levels were significantlyhigher than the control group after 24 h of transport(p<0.05).Both gill and liver tissues of fish were damaged to different degrees due to the stress of transport.heat shock protein 70 gene expression decreased after transport whileheat shock protein 90 gene expression increased after transport.Both tumour necrosis factor-alpha(TNF-α)and interleukin-1β(IL-1β)gene expression numbers decreased after transport,while the VC-50 mg/β-CD group showed the greatest decrease in interleukin-1βnumbers,which was significantly lower than the control group(p<0.05).In conclusion,VC-50 mg/β-CD and EU-10 mg+VC-50 mg/β-CD were more advantageous in transport and more suitable forhigh density transport.3.Effect of three additives on the physiology,biochemistry and abundance of intestinal flora of juvenile Pelteobagrus fulvidraco on a temporary basisThe three additives(Astragalus polysaccharide APS,Chitosan COS and Xylo-oligosaccharide XOS)were divided into high concentration and low concentration and added to the water for temporary storage of juvenile yellow catfish for three days,and then transported for 8 hours.The relieving effects of the three additives on the transportation stress of juvenile yellow catfish were analyzed.The serum cortisol of fry on the third day of the transient group withhigh concentration of Astragalus polysaccharide(hereafter AH,H for High concentration and L for Low concentration)after transportation was significantlyhigher than the cortisol level after transportation,COS transienthad a decrease in cortisol level after transportation,and XOS did not significantly improve the stress status of fish after transportation.both APS and XOS could increase the fish Ig M,complement The AH and CH groups reduced the levels of SOD and CAT activity in fish and reduced the stress response to transport.The APS group was found to reduce the activity of Casp-3 and Casp-9 in the intestinal tract of fish in the fish supplemented with the APS respite experimental group and COS respite experimental group.APS could increase the number of intestinal cupped cells and theheight of intestinal villi in fish and improve the structural integrity of the intestine.The AL group showed its great advantage after 8 h of transport,significantly greater than the control group(p<0.05).APS could effectively increase the abundance of Clostridium phylum in fry.In conclusion,the effect of APS transient at 50 mg/L in water on juvenile Pelteobagrus fulvidraco after transport was more significant. |
PDF Full Text Request