| Fishmeal production is decreasing,and soybean meal has become one of the main alternative raw materials for fishmeal.However,compared to fishmeal,the presence of anti-nutritional factors in soybean meal can bring harm to fish and reduce growth performance.In particular,soy saponins are thermally stable,and the effective way to get rid of them is ethanol extraction,which is costly and not easy to reach.The untreated soybean meal with 1.9%-2.5% soy saponins can cause increased permeability of fish intestinal mucosal epithelial cells,which can lead to passive uptake of antigenic substances and cause enteritis.Therefore,in this study,the representative species of aquatic crustaceans and omnivorous economic species,crayfish(Procambarus clarkii)and hybrid croaker(Pelteobagrus fulvidraco♀×Pelteobagrus vachelli♂),were selected to investigate the effects of soy saponins on their growth,immunity and intestinal health,respectively:1.Effects of soybean saponins on growth,immunity and intestinal structure of crayfishIn order to investigate the effects of soybean saponins on growth,immunity and intestinal structure of Procambarus clarkii,0%,0.50%,1.00%,2.00% and 4.00% of soybean saponins were added to the basal diet with fish meal,shrimp meal and corn protein concentrate as protein sources,respectively.Procambarus clarkii with an initial weight of(11.29±0.10)g were fed with the five kinds of isonitrogenous and isolipid diets respectively and were recorded as D0,D0.5,D1.0,D2.0 and D4.0 treatment groups.Three replicates were set for each group,with 20 shrimp per replicate.After the 4-week feeding experiment,the growth indexes,body composition,serum and hepatopancreas immunity,antioxidant enzyme activities and blood lymphocyte composition were determined,and H&E sections were prepared.The results showed as follows:(1)Compared with the D0 group,the specific growth rate and weight gain rate of shrimp in the soybean saponin supplemented group were significantly decreased,the feed conversion ratio was significantly increased,and the survival rate of shrimp in the D2.0 group was significantly decreased,dressing percentage was significantly lower in the D2.0 and D4.0 groups(P<0.05).(2)Diets supplemented with0.5% to 4.0% soybean saponins had no significant effects on the contents of dry matter crude protein,ether extract and ash in muscle of crayfish(P>0.05).(3)With the increase of dietary saponin level,the proportion of small granule cells in blood cells first decreased and then increased,while the proportion of clear cells first increased and then decreased.D1.0 group had the lowest proportion of SGC and the highest proportion of HC,which dramatically varied from D0 group(P<0.05).Except for D2.0 group,there was no significant difference in large granule cells in other groups(P>0.05).(4)With the increase of dietary saponin level,the activities of serum AKP,PO,hepatopancreas T-AOC,T-SOD and CAT were firstly increased and then decreased,but only the activity of AKP was significantly decreased when the level of saponin exceeded 2.0%(P<0.05);The activity of serum ACP decreased first and then increased.Hepatopancreas MDA decreased significantly(P<0.05).Compared with D0 group,ACP activity in D0.5 group was significantly decreased,while AKP and PO activities were significantly increased(P<0.05);MDA levels in D1.0 group were significantly decreased,while T-AOC,T-SOD and CAT activities were significantly increased(P<0.05).(5)With the increase of the level of dietary saponins,the connective tissue connectivity of the hindgut of crayfish deteriorated,Significant blood cell infiltration and epithelial cells with nuclear inward migration and abnormal shape were observed.In conclusion,dietary supplementation of a certain level of soy saponins has significant negative effects on the growth performance,immune and antioxidant capacity and intestinal structure of crayfish.When the level of soy saponins exceeds 0.50%,the growth and immunity of crayfish are inhibited,and typical enteritis occurs.Therefore,selection of feed in crayfish aquaculture requires control of saponin content of no more than 0.50%.2.Effects of soybean saponins on growth,immunity and intestinal health of hybrid yellow catfishTo investigate the effects of soybean saponins on growth,immunity and intestinal health of hybrid yellow catfish(Pelteobagrus fulvidraco♀×Pelteobagrus vachelli♂),0%,0.20%,0.40%,0.80%,1.60% and 4.00% soybean saponins were added to the basal diet with fish meal,shrimp meal and corn protein concentrate as protein sources,respectively.Hybrid yellow catfish with initial mass of(1.0±0.17)g were fed with the six kinds of isonitrogenous and isolipid diets respectively and were recorded as D0,D0.2,D0.4,D0.8,D1.6 and D4.0 treatment groups.There were 3 replicates in each group and 30 fish in each replicate.After the 60 d feeding experiment,the growth indexes,body composition,immune and antioxidant enzyme activities,tight junction protein and inflammatory factor expressions were measured.H&E sections and TUNEL sections were prepared,and the intestinal flora composition was analyzed by 16 S r RNA gene sequencing.The results are shown below:(1)In comparison to the D0 group,not only the specific growth rate but weight gain rate in the treatment group supplemented with soybean saponin were significantly decreased(P<0.05),and the feed conversion ratio was significantly increased(P<0.05).Body protein content and muscle fat content of test fish decreased first and then increased,body fat content and muscle protein content increased first and then decreased.(2)With the increase of dietary saponin level,serum T-AOC continued to decrease,the activities of AKP,NO and CAT increased first and then decreased,and the activity of ACP decreased first and then increased.(3)Significantly higher activity of liver ACP was observed in D0.8,D1.6 and D4.0 groups in comparison to other groups;The liver CAT activity of D0 and D4.0 groups was significantly lower than that of the other groups(P<0.05).The liver T-AOC activity increased first and then decreased.The content of MDA in treatment groups was significantly low in comparison to D0 group and was decreased gradually with the increase of saponins level.The liver T-SOD decreased first and then increased.(4)Besides,with the increasing supplement of soybean saponins,the activities of AKP and ACP in distal intestinal tract were decreased continuously,the activities of TAOC and T-SOD decreased first and then increased,and the activities of LZM increased first and then decreased with the increase of dietary saponin level.The T-AOC of distal intestinal tract in D0 and D0.2 groups was dramatically higher in comparison to D0.4 and D0.8 groups and dramatically lower in comparison to D1.6 and D4.0 groups(P<0.05).We found that the T-SOD activity in D0.4,D0.8,D1.6 and D4.0 groups was dramatically higher in comparison to D0.2 group(P<0.05),and higher MDA content in D0 group was observed in comparison to the treatment groups.(5)H&E sections showed that compared with D0 group,the relative height of distal intestinal folds in D0.4,D0.8,D1.6 and D4.0 groups were significantly decreased,the relative width of lamina propria was significantly increased,and the relative depth of recess in D0.8,D1.6 and D4.0 groups was significantly increased(P<0.05).TUNEL sections showed that apoptotic cells existed in all groups,and the apoptotic cells increased with the increase of saponins level.(6)With the continuous increase of dietary saponins,m RNA expression levels of OCC,ZO-1,CL-1,CL-2,CL-5,TGF-β and IL-10 in distal intestinal tract were decreased,while m RNA expression level of MAPKAPK1 was increased.m RNA expression levels of IL-1β,IL-8,IL-15 and TNF-α were increased first and then decreased.(7)The composition of the dominant flora in the intestine of the hybrid Pelteobagrus fulvidraco was significantly altered by the addition of soy saponins to the feed,and a significant clustering phenomenon was observed.The abundance of opportunistic pathogens such as Ochrobactrum,Delftia and Acinetobacter,and Sphingomonas,which is involved in the hydrolysis of saponins,increased in the treatment group with saponins,and the abundance of Bacillaceae-Bacillus and Oceanicaulis were slightly less abundant.In conclusion,dietary supplementation with a certain level of soy saponin has significant negative effects on growth performance,immune and antioxidant capacities and intestinal health of hybrid yellow catfish.When the level of soy saponin exceeds 0.40%,the growth and immunity of hybrid yellow catfish are inhibited,and a typical phenomenon of enteritis appears.Therefore,the content of saponins should be controlled less than 0.40% when selecting diets for yellow catfish commercial culture. |
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