Background In intensive aquaculture systems,the frequent incidence of enteritis reduces production efficiency and results in significant economic losses.Protein feeds account for 40%–60%of aquafeed expenses,and with ...Background In intensive aquaculture systems,the frequent incidence of enteritis reduces production efficiency and results in significant economic losses.Protein feeds account for 40%–60%of aquafeed expenses,and with the growth of intensive aquaculture,demand for fishmeal as a key protein source outstrips supply,driving up prices.This study investigated the therapeutic potential of reducing dietary protein levels by 3%and adding enzymatic cottonseed protein(ECP)in juvenile yellow catfish with dextran sulfate sodium(DSS)-induced enteritis.Methods A total of 1,260 healthy juvenile yellow catfish(Pelteobagrus fulvidraco),with an average body weight of 5.90±0.05 g,were randomly allocated into 7 experimental groups,each with 3 replicates.The fish were fed one of seven diets for 10 weeks:a normal-protein diet(42%;NP)and 6 low-protein diets(39%;LP)supplemented with graded levels of ECP at 0%(ECP0),1%(ECP1),2%(ECP2),3%(ECP3),4%(ECP4),and 5%(ECP5),respectively.Subsequently,48 fish from each group were selected to receive 1 mL of 6%DSS solution.Results Our findings demonstrated that:(1)The DSS+ECP0 group aggravated DSS-induced enteritis in juvenile yellow catfish compared to the DSS+NP group.(2)Dietary supplementation of ECP in LP diets significantly enhanced the enzymatic activity and levels of immunoreactive substances,including LZM,C3,C4,and ACP(P<0.05).Mechanistically,first,ECP supplementation modulated macrophage polarization by inhibiting the M1 phenotype while promoting the M2 phenotype,potentially through the JAK-STAT signaling pathway;second,dietary ECP suppressed the phosphorylation cascade of key necroptosis-related proteins,including RIP1,RIP3,and MLKL,potentially via the NF-κB and MAPK signaling pathways.(3)The DSS+ECP2 group demonstrated comparable or superior efficacy to the DSS+NP group in mitigating DSS-induced intestinal enteritis.Conclusions Our results demonstrated that ECP can alleviate DSS-induced enteritis by regulating macrophage polarization and reducing necroptosis.Furthermore,ECP supplementation effectively counteracted the exacerbation of enteritis caused by dietary protein reduction.These findings highlighted the effectiveness and feasibility of ECP in alleviating enteritis and saving protein.展开更多
Over the past five years, an epidemic disease broke out in Pelteobagrus fulvidraco ponds of Zhejiang Province. The diseased fish mainly exhibits head splitting and surface bleeding; dissection results reveal hepatonep...Over the past five years, an epidemic disease broke out in Pelteobagrus fulvidraco ponds of Zhejiang Province. The diseased fish mainly exhibits head splitting and surface bleeding; dissection results reveal hepatonephromegaly and abdominal bleeding. A bacterial strain HSY201301 was isolated from the liver tissue of P. fulvidraco with typical symptoms. Artificial infection experiment confirmed that the isolated strain had a strong virulence to healthy P. fidvidraco, leading to similar symptoms to naturally infected P. fulvidraco. The isolated strain was identified as an Edwardsiella tarda strain according to conventional morphological, physiological, biochemical characteristics and 16S rRNA gene sequence. Results of drug susceptibility test indicated that the isolated strain was sensitive to cipro- floxacin, doxitard, penicillin, doxycycline, and rocephin. This study laid solid foundation for effective prevention and control of E. tarda.展开更多
Although the effects of diet on intestinal microbiotas have been well investigated,the effect of feeding time on the rhythm of gut microbiota remains uncertain.A 9-week feeding trial on Pelteobagrus fulvidraco was con...Although the effects of diet on intestinal microbiotas have been well investigated,the effect of feeding time on the rhythm of gut microbiota remains uncertain.A 9-week feeding trial on Pelteobagrus fulvidraco was conducted.Two triplicate groups of fish were fed identically either at 8:00(day)or at 20:00(night).After 9 weeks,three fish from each cage were sacrificed every 4 h for 24 h.The intestinal contents were analyzed using high-throughput sequencing.Three phyla(Fusobacteria,Proteobacteria,and Verrucomicrobia),and three genera(Cetobacterium,Akkermansia,and Clostridium)were dominant at every time point.Moreover,33.02%of detected amplicon sequence variants showed cyclical variations in fish fed at 20:00,and 3.47%in fish fed at 8:00.Among the top 20 genera,17 showed cyclical variations in the 20:00 group,and only two in the 8:00 group.Rhodobacter,Ralstonia,Mycobacterium,Lactococcus,Halomonas,Akkermansia,and Acinetobacter contributed more to the predicted functional pathways.Moreover,144 and 38 pathways exhibited daily cyclical fluctuations in fish fed at 20:00 and 8:00,respectively.Overall,certain intestinal microorganisms showed a circadian rhythm in P.fulvidraco,and this circadian rhythm was affected by shifted feeding times.展开更多
Androgenesis was the especial zoogamy that the germ plasma of offspring was from the agnate. In this study the eggs of Yellow catfish （Pelteobagrus fulvidraco） were irradiated by UV suspending in the synthetic ovari...Androgenesis was the especial zoogamy that the germ plasma of offspring was from the agnate. In this study the eggs of Yellow catfish （Pelteobagrus fulvidraco） were irradiated by UV suspending in the synthetic ovarian fluid （OF）, and the total dosage of UV irradiation was 220 mJ·cm^-2. Diploid could be induced by heat shock （40℃, 2 min, 3 min） with different time period after fertilization （15-37 min）. The result showed that heat shock with 2 min was better than 3 min; there were two apices of induction in 17-21 min and 27-31 min after fertilization. The highest hatching rate was 3.30% at 29 min after fertilization, and the difference between two apices of induction was unobvious.展开更多
[Objectives] This study was conducted to study early reproduction techniques of yellow catfish(Pelteobagrus fulvidraco) in Jianghan Plain. [Methods] Parents of P. fulvidraco were cultured by the methods of artificial ...[Objectives] This study was conducted to study early reproduction techniques of yellow catfish(Pelteobagrus fulvidraco) in Jianghan Plain. [Methods] Parents of P. fulvidraco were cultured by the methods of artificial temperature control and nutrition enhancement. [Results] After culture, the body weight, gonad weight, maturity coefficient and egg diameter of P. fulvidraco increased gradually. Up to April 30, the gonad weight of the female parents of P. fulvidraco cultured in greenhouses was significantly higher than that of the parents under natural conditions(P<0.05), 54% higher than that of the parents naturally cultured at the same period;the maturity coefficient of the parents cultured under strengthened conditions was also significantly higher than that of the parents under natural conditions at the same period(P<0.05);and the ovaries of the strengthened parents were orange yellow and full of eggs, and the number of eggs per fish was relatively high. In early May, the parents cultured under strengthened conditions were induced to spawn artificially. The average induced spawning rate and fertilization rate reached 86.7% and 71.6%, respectively, reaching the respective normal level. The gonad maturity of P. fulvidraco cultured under strengthened conditions was 15 d earlier than that under natural conditions, resulting in mass production of early-propagated larvae of P. fulvidraco. [Conclusions] In Jianghan plain area, artificial propagation can be achieved in early May by means of artificial temperature control and strengthened culture, which is 20 d ahead of natural conditions.展开更多
This experiment was conducted to investigate the effects of dietary arginine levels on growth performance, body composition, serum biochemical indices and resistance ability against ammonia-nitrogen stress in juvenile...This experiment was conducted to investigate the effects of dietary arginine levels on growth performance, body composition, serum biochemical indices and resistance ability against ammonia-nitrogen stress in juvenile yellow catfish(Pelteobagrus fulvidraco). Five isonitrogenous and isolipidic diets(42%protein and 9% lipid) were formulated to contain graded levels of arginine(2.44%, 2.64%, 2.81%, 3.01% and3.23% of diet), by supplementing L-Arginine HCI. Seven hundred juvenile yellow catfish with an initial average body weight of 1.13 ± 0.02 g were randomly divided into 5 groups with 4 replicates of 35 fish each and each group was fed one of the diets. After 56 d feeding, fish were exposed to 100 mg/L of ammonia-nitrogen for 72 h. The results showed that weight gain(WG) and specific growth rate(SGR) in2.64% and 2.81% groups were significantly higher than those in 3.23% group(P < 0.05). The feed conversation ratio(FCR) in 2,64%, 2,81% and 3.01% groups was significantly decreased when compared with3,23% group. The protein efficiency ratio(PER) in 2.64% group was significantly higher than that in 2.44%and 3.23% groups(P < 0.05). The condition factor(CF) of fish was significantly higher in 2.81% group than that in 2,44% group(P < 0.05). Dietary arginine levels had no significant effect on hepatosomatic index(HSI), viscerosomatic index(VSI), and whole-body dry matter, crude protein, crude lipid, ash contents, as well as serum total protein(TP), triglyceride(TG), glucose(GLU), urea nitrogen(UN) contents and aspartate aminotransferase(AST), alanine aminotransferase(ALT) activities(P> 0.05). After the fish were challenged to ammonia-nitrogen for 72 h, their cumulative mortality rate in 2.81% group was significantly lower than that in 2.44% group(P < 0.05). The results suggested that dietary arginine level at 2.81%could optimize anti-ammonia-nitrogen stress ability of juvenile yellow catfish and a level of 3.23%arginine seemed to depress the growth performance of fish and decreased their tolerance to the ammonia-nitrogen stress under current study. A quadratic regression analysis based on WG indicated that the optimal dietary arginine requirement of juvenile yellow catfish was estimated to be 2.74% of the diet(6.45% of dietary protein) under current culture conditions.展开更多
In this study,three members of the Bmp family were cloned and characterized in yellow catfish Pelteobagrus fulvidraco,including Bmp2a,Bmp4 and Bmp9.The predicted amino acid sequences of P.fulvidraco Bmp2a,Bmp4 and Bmp...In this study,three members of the Bmp family were cloned and characterized in yellow catfish Pelteobagrus fulvidraco,including Bmp2a,Bmp4 and Bmp9.The predicted amino acid sequences of P.fulvidraco Bmp2a,Bmp4 and Bmp9 showed the characteristic domains of the Bmp family,including an N-terminal signal peptide,Arg-X-XArg site,TGF-βfamily signature and seven conserved cysteines,indicating that function is likely to have been conserved during evolution.mRNAs of the three Bmp genes had a variable level of expression in tissues.Compared to the control diet,a high fat diet tended to down-regulate the mRNA expression of Bmp2a,Bmp4 and Bmp9 in mesenteric fat,liver and ovary,while it tended to up-regulate their mRNA levels in muscle and kidney.The responses to dietary lipid status and the potential role in lipid metabolism have not previously been reported and reinforces the idea of their multiple functions.Our findings provide the first data about the potential role of the Bmp family in lipid metabolism in teleost.展开更多
Enzymatic cottonseed protein(ECP)is a functional peptide product reported to have antioxidant and immunomodulatory properties.This study focused on how the intestinal apical junction complex(AJC)structure,microbial co...Enzymatic cottonseed protein(ECP)is a functional peptide product reported to have antioxidant and immunomodulatory properties.This study focused on how the intestinal apical junction complex(AJC)structure,microbial composition,growth performance,and digestive and absorptive capacity were affected by adding ECP to diets with a 3% crude protein(CP)reduction.A total of 1260 healthy juvenile yellow catfish weighing 5.90±0.05 g were randomly assigned to seven experimental groups,each consisting of three replicates.A normal protein(NP)diet(42%CP)or one of six low protein(LP)diets(39%CP)with differing amounts of ECP(0%,1%,2%,3%,4%,and 5%,respectively)given for ten weeks.Dietary CP levels that were lowered by 3%(from 42%to 39%)disrupted the intestinal AJC structure and reduced growth performance,including specific growth rate(SGR;P=0.042)and feed intake(FI;P=0.001)and digestive and absorptive capacity,including the activities of alkaline phosphatase(AKP;P<0.001),γ-glutamyl transpeptidase(γ-GT;P<0.001),Na^(+)/K^(+)-ATPase(P<0.001),pepsin(P<0.001),lipase(P=0.009),amylase(P<0.001),chymotrypsin(P<0.001),and carboxypeptidase(CPs;P=0.005).Adding 2%ECP to the LP diets(39%CP)improved SGR(P=0.001),FI(P<0.001),pepsin activity(P<0.001),the activities of γ-GT(P<0.001),AKP(P<0.001),lipase(P<0.001),amylase(P<0.001),Na^(+)/K^(+)-ATPase(P<0.001),chymotrypsin(P<0.001),aminopeptidases(Aps;P<0.001),and CPs(P<0.001).The factors that control the expression of peptide transporter 1(PepT1),such as nuclear factor erythroid 2-related factor 2(nrf2),Janus kinase 2(jak2),caudal type homeobox transcription factor 2(CDX2),and specificity protein 1(SP1),as well as those that affect its function,such as protein sodium/hydrogen exchange isoform 3(NHE3)and PDZ domain containing 1(PDZK1),may be responsible for the increase in the expression of PepT1(P=0.008).Furthermore,the Ras homolog family member A(RhoA)/Rho-associated kinase(ROCK)signaling pathway may be involved in improving intestinal AJC structure.ECP also increased the relative abundance of beneficial bacteria,including Fusobacteria,Firmicutes,Cetobacterium,and Acinetobacter,while decreasing that of pathogenic bacteria,such as Spirochaetes,Actinomycetes,Brevinema,and Plesiomonas.A 3% decrease in dietary CP levels and supplementation with 2%ECP restored growth performance,intestinal structural indices,and digestive and absorptive capacity to levels equivalent to or better than those of the NP.Furthermore,chymotrypsin and percentage weight gain broken-line regression analysis revealed that the optimal ECP additions for juvenile catfish were 2.08% and 2.2%,respectively.展开更多
基金National Science Fund for Distinguished Young Scholars of China(32425056)National Natural Science Foundation of China(U23A20250)+2 种基金the earmarked fund for CARS(CARS-45)the National Key R&D Program of China(2023YFD2400600)Sichuan Innovation Team of National Modern Agricultural Industry Technology System(SCCXTD-2024-15).
文摘Background In intensive aquaculture systems,the frequent incidence of enteritis reduces production efficiency and results in significant economic losses.Protein feeds account for 40%–60%of aquafeed expenses,and with the growth of intensive aquaculture,demand for fishmeal as a key protein source outstrips supply,driving up prices.This study investigated the therapeutic potential of reducing dietary protein levels by 3%and adding enzymatic cottonseed protein(ECP)in juvenile yellow catfish with dextran sulfate sodium(DSS)-induced enteritis.Methods A total of 1,260 healthy juvenile yellow catfish(Pelteobagrus fulvidraco),with an average body weight of 5.90±0.05 g,were randomly allocated into 7 experimental groups,each with 3 replicates.The fish were fed one of seven diets for 10 weeks:a normal-protein diet(42%;NP)and 6 low-protein diets(39%;LP)supplemented with graded levels of ECP at 0%(ECP0),1%(ECP1),2%(ECP2),3%(ECP3),4%(ECP4),and 5%(ECP5),respectively.Subsequently,48 fish from each group were selected to receive 1 mL of 6%DSS solution.Results Our findings demonstrated that:(1)The DSS+ECP0 group aggravated DSS-induced enteritis in juvenile yellow catfish compared to the DSS+NP group.(2)Dietary supplementation of ECP in LP diets significantly enhanced the enzymatic activity and levels of immunoreactive substances,including LZM,C3,C4,and ACP(P<0.05).Mechanistically,first,ECP supplementation modulated macrophage polarization by inhibiting the M1 phenotype while promoting the M2 phenotype,potentially through the JAK-STAT signaling pathway;second,dietary ECP suppressed the phosphorylation cascade of key necroptosis-related proteins,including RIP1,RIP3,and MLKL,potentially via the NF-κB and MAPK signaling pathways.(3)The DSS+ECP2 group demonstrated comparable or superior efficacy to the DSS+NP group in mitigating DSS-induced intestinal enteritis.Conclusions Our results demonstrated that ECP can alleviate DSS-induced enteritis by regulating macrophage polarization and reducing necroptosis.Furthermore,ECP supplementation effectively counteracted the exacerbation of enteritis caused by dietary protein reduction.These findings highlighted the effectiveness and feasibility of ECP in alleviating enteritis and saving protein.
文摘Over the past five years, an epidemic disease broke out in Pelteobagrus fulvidraco ponds of Zhejiang Province. The diseased fish mainly exhibits head splitting and surface bleeding; dissection results reveal hepatonephromegaly and abdominal bleeding. A bacterial strain HSY201301 was isolated from the liver tissue of P. fulvidraco with typical symptoms. Artificial infection experiment confirmed that the isolated strain had a strong virulence to healthy P. fidvidraco, leading to similar symptoms to naturally infected P. fulvidraco. The isolated strain was identified as an Edwardsiella tarda strain according to conventional morphological, physiological, biochemical characteristics and 16S rRNA gene sequence. Results of drug susceptibility test indicated that the isolated strain was sensitive to cipro- floxacin, doxitard, penicillin, doxycycline, and rocephin. This study laid solid foundation for effective prevention and control of E. tarda.
基金Supported by the Sichuan Science and Technology Program(Nos.2021YFYZ0015,2023NSFSC0241)。
文摘Although the effects of diet on intestinal microbiotas have been well investigated,the effect of feeding time on the rhythm of gut microbiota remains uncertain.A 9-week feeding trial on Pelteobagrus fulvidraco was conducted.Two triplicate groups of fish were fed identically either at 8:00(day)or at 20:00(night).After 9 weeks,three fish from each cage were sacrificed every 4 h for 24 h.The intestinal contents were analyzed using high-throughput sequencing.Three phyla(Fusobacteria,Proteobacteria,and Verrucomicrobia),and three genera(Cetobacterium,Akkermansia,and Clostridium)were dominant at every time point.Moreover,33.02%of detected amplicon sequence variants showed cyclical variations in fish fed at 20:00,and 3.47%in fish fed at 8:00.Among the top 20 genera,17 showed cyclical variations in the 20:00 group,and only two in the 8:00 group.Rhodobacter,Ralstonia,Mycobacterium,Lactococcus,Halomonas,Akkermansia,and Acinetobacter contributed more to the predicted functional pathways.Moreover,144 and 38 pathways exhibited daily cyclical fluctuations in fish fed at 20:00 and 8:00,respectively.Overall,certain intestinal microorganisms showed a circadian rhythm in P.fulvidraco,and this circadian rhythm was affected by shifted feeding times.
基金Supported by Science Project of Heilongjiang Province(GC03B510)
文摘Androgenesis was the especial zoogamy that the germ plasma of offspring was from the agnate. In this study the eggs of Yellow catfish （Pelteobagrus fulvidraco） were irradiated by UV suspending in the synthetic ovarian fluid （OF）, and the total dosage of UV irradiation was 220 mJ·cm^-2. Diploid could be induced by heat shock （40℃, 2 min, 3 min） with different time period after fertilization （15-37 min）. The result showed that heat shock with 2 min was better than 3 min; there were two apices of induction in 17-21 min and 27-31 min after fertilization. The highest hatching rate was 3.30% at 29 min after fertilization, and the difference between two apices of induction was unobvious.
基金Supported by The Technological Innovation Special Project of Hubei Province(2018ABA104)
文摘[Objectives] This study was conducted to study early reproduction techniques of yellow catfish(Pelteobagrus fulvidraco) in Jianghan Plain. [Methods] Parents of P. fulvidraco were cultured by the methods of artificial temperature control and nutrition enhancement. [Results] After culture, the body weight, gonad weight, maturity coefficient and egg diameter of P. fulvidraco increased gradually. Up to April 30, the gonad weight of the female parents of P. fulvidraco cultured in greenhouses was significantly higher than that of the parents under natural conditions(P<0.05), 54% higher than that of the parents naturally cultured at the same period;the maturity coefficient of the parents cultured under strengthened conditions was also significantly higher than that of the parents under natural conditions at the same period(P<0.05);and the ovaries of the strengthened parents were orange yellow and full of eggs, and the number of eggs per fish was relatively high. In early May, the parents cultured under strengthened conditions were induced to spawn artificially. The average induced spawning rate and fertilization rate reached 86.7% and 71.6%, respectively, reaching the respective normal level. The gonad maturity of P. fulvidraco cultured under strengthened conditions was 15 d earlier than that under natural conditions, resulting in mass production of early-propagated larvae of P. fulvidraco. [Conclusions] In Jianghan plain area, artificial propagation can be achieved in early May by means of artificial temperature control and strengthened culture, which is 20 d ahead of natural conditions.
基金supported by the National Natural Science Foundation of China (31402307)the construction of public service platform for the evaluation of the value of aquatic feed and feed additives in Guangdong Province(2015A040404033)
文摘This experiment was conducted to investigate the effects of dietary arginine levels on growth performance, body composition, serum biochemical indices and resistance ability against ammonia-nitrogen stress in juvenile yellow catfish(Pelteobagrus fulvidraco). Five isonitrogenous and isolipidic diets(42%protein and 9% lipid) were formulated to contain graded levels of arginine(2.44%, 2.64%, 2.81%, 3.01% and3.23% of diet), by supplementing L-Arginine HCI. Seven hundred juvenile yellow catfish with an initial average body weight of 1.13 ± 0.02 g were randomly divided into 5 groups with 4 replicates of 35 fish each and each group was fed one of the diets. After 56 d feeding, fish were exposed to 100 mg/L of ammonia-nitrogen for 72 h. The results showed that weight gain(WG) and specific growth rate(SGR) in2.64% and 2.81% groups were significantly higher than those in 3.23% group(P < 0.05). The feed conversation ratio(FCR) in 2,64%, 2,81% and 3.01% groups was significantly decreased when compared with3,23% group. The protein efficiency ratio(PER) in 2.64% group was significantly higher than that in 2.44%and 3.23% groups(P < 0.05). The condition factor(CF) of fish was significantly higher in 2.81% group than that in 2,44% group(P < 0.05). Dietary arginine levels had no significant effect on hepatosomatic index(HSI), viscerosomatic index(VSI), and whole-body dry matter, crude protein, crude lipid, ash contents, as well as serum total protein(TP), triglyceride(TG), glucose(GLU), urea nitrogen(UN) contents and aspartate aminotransferase(AST), alanine aminotransferase(ALT) activities(P> 0.05). After the fish were challenged to ammonia-nitrogen for 72 h, their cumulative mortality rate in 2.81% group was significantly lower than that in 2.44% group(P < 0.05). The results suggested that dietary arginine level at 2.81%could optimize anti-ammonia-nitrogen stress ability of juvenile yellow catfish and a level of 3.23%arginine seemed to depress the growth performance of fish and decreased their tolerance to the ammonia-nitrogen stress under current study. A quadratic regression analysis based on WG indicated that the optimal dietary arginine requirement of juvenile yellow catfish was estimated to be 2.74% of the diet(6.45% of dietary protein) under current culture conditions.
基金The study was funded by National Natural Science Foundation of China(Grant nos.:31572605,31001101)Project of Innovative Group for Excellent Young Scientists in Universities of Hubei Province from Hubei Provincial Department of Education(T201933).
文摘In this study,three members of the Bmp family were cloned and characterized in yellow catfish Pelteobagrus fulvidraco,including Bmp2a,Bmp4 and Bmp9.The predicted amino acid sequences of P.fulvidraco Bmp2a,Bmp4 and Bmp9 showed the characteristic domains of the Bmp family,including an N-terminal signal peptide,Arg-X-XArg site,TGF-βfamily signature and seven conserved cysteines,indicating that function is likely to have been conserved during evolution.mRNAs of the three Bmp genes had a variable level of expression in tissues.Compared to the control diet,a high fat diet tended to down-regulate the mRNA expression of Bmp2a,Bmp4 and Bmp9 in mesenteric fat,liver and ovary,while it tended to up-regulate their mRNA levels in muscle and kidney.The responses to dietary lipid status and the potential role in lipid metabolism have not previously been reported and reinforces the idea of their multiple functions.Our findings provide the first data about the potential role of the Bmp family in lipid metabolism in teleost.
基金National Science Fund for Distinguished Young Scholars of China(32425056)the earmarked fund for CARS(CARS-45)+1 种基金the National Key R&D Program of China(2023YFD2400600)Sichuan Innovation Team of National Modern Agricultural Industry Technology System(SCCXTD-2024-15).
文摘Enzymatic cottonseed protein(ECP)is a functional peptide product reported to have antioxidant and immunomodulatory properties.This study focused on how the intestinal apical junction complex(AJC)structure,microbial composition,growth performance,and digestive and absorptive capacity were affected by adding ECP to diets with a 3% crude protein(CP)reduction.A total of 1260 healthy juvenile yellow catfish weighing 5.90±0.05 g were randomly assigned to seven experimental groups,each consisting of three replicates.A normal protein(NP)diet(42%CP)or one of six low protein(LP)diets(39%CP)with differing amounts of ECP(0%,1%,2%,3%,4%,and 5%,respectively)given for ten weeks.Dietary CP levels that were lowered by 3%(from 42%to 39%)disrupted the intestinal AJC structure and reduced growth performance,including specific growth rate(SGR;P=0.042)and feed intake(FI;P=0.001)and digestive and absorptive capacity,including the activities of alkaline phosphatase(AKP;P<0.001),γ-glutamyl transpeptidase(γ-GT;P<0.001),Na^(+)/K^(+)-ATPase(P<0.001),pepsin(P<0.001),lipase(P=0.009),amylase(P<0.001),chymotrypsin(P<0.001),and carboxypeptidase(CPs;P=0.005).Adding 2%ECP to the LP diets(39%CP)improved SGR(P=0.001),FI(P<0.001),pepsin activity(P<0.001),the activities of γ-GT(P<0.001),AKP(P<0.001),lipase(P<0.001),amylase(P<0.001),Na^(+)/K^(+)-ATPase(P<0.001),chymotrypsin(P<0.001),aminopeptidases(Aps;P<0.001),and CPs(P<0.001).The factors that control the expression of peptide transporter 1(PepT1),such as nuclear factor erythroid 2-related factor 2(nrf2),Janus kinase 2(jak2),caudal type homeobox transcription factor 2(CDX2),and specificity protein 1(SP1),as well as those that affect its function,such as protein sodium/hydrogen exchange isoform 3(NHE3)and PDZ domain containing 1(PDZK1),may be responsible for the increase in the expression of PepT1(P=0.008).Furthermore,the Ras homolog family member A(RhoA)/Rho-associated kinase(ROCK)signaling pathway may be involved in improving intestinal AJC structure.ECP also increased the relative abundance of beneficial bacteria,including Fusobacteria,Firmicutes,Cetobacterium,and Acinetobacter,while decreasing that of pathogenic bacteria,such as Spirochaetes,Actinomycetes,Brevinema,and Plesiomonas.A 3% decrease in dietary CP levels and supplementation with 2%ECP restored growth performance,intestinal structural indices,and digestive and absorptive capacity to levels equivalent to or better than those of the NP.Furthermore,chymotrypsin and percentage weight gain broken-line regression analysis revealed that the optimal ECP additions for juvenile catfish were 2.08% and 2.2%,respectively.
