Intestinal Digestive Enzyme Activities Research Articles

Effects of high NaHCO3 alkalinity on growth, tissue structure, digestive enzyme activity, and gut microflora of grass carp juvenile.

With the gradual decrease in freshwater resources, the available space for freshwater aquaculture is diminishing. As a result, saline-alkaline water aquaculture has emerged as a crucial method to fulfill the increasing demand. This study investigates the impact of alkaline water on the growth performance, tissues (gill, liver, and kidney), digestive enzyme activity, and intestinal microbiology in grass carp (Ctenopharyngodon idella). The aquarium conditions were set with sodium bicarbonate (18mmol/L (LAW), 32mmol/L (HAW)) to simulate the alkaline water environment. A freshwater group was the control (FW). The experimental fish were cultured for 60days. The findings revealed that NaHCO3 alkaline stress significantly reduced growth performance, caused alterations in the structural morphology of gill lamellae, liver, and kidney tissues, and led to decreased activity of intestinal trypsin and lipase amylase (P < 0.05). Analysis of 16S rRNA sequences demonstrated that alkalinity influenced the abundance of dominant bacterial phyla and genera. Proteobacteria showed a significant decrease under alkaline conditions, while Firmicutes exhibited a significant increase (P < 0.05). Furthermore, alkalinity conditions significantly reduced the abundance of bacteria involved in protein, amino acid, and carbohydrate metabolism, cell transport, cell decomposition, and environmental information processing. Conversely, the abundance of bacteria associated with lipid metabolism, energy metabolism, organic systems, and disease functional flora increased significantly under alkalinity conditions (P < 0.05). In conclusion, this comprehensive study indicates that alkalinity stress adversely affected the growth performance of juvenile grass carp, likely due to tissue damage, reduced activity of intestinal digestive enzymes, and alterations in intestinal microorganisms.

Effect of Purslane (Portulaca oleracea L.) on Intestinal Morphology, Digestion Activity and Microbiome of Chinese Pond Turtle (Mauremys reevesii) during Aeromonas hydrophila Infection.

Large-scale mortality due to Aeromonas hydrophila (A. hydrophila) infection has considerably decreased the yield of the Chinese pond turtle (Mauremys reevesii). Purslane is a naturally active substance with a wide range of pharmacological functions, but its antibacterial effect on Chinese pond turtles infected by A. hydrophila infection is still unknown. In this study, we investigated the effect of purslane on intestinal morphology, digestion activity, and microbiome of Chinese pond turtles during A. hydrophila infection. The results showed that purslane promoted epidermal neogenesis of the limbs and increased the survival and feeding rates of Chinese pond turtles during A. hydrophila infection. Histopathological observation and enzyme activity assay indicated that purslane improved the intestinal morphology and digestive enzyme (α-amylase, lipase and pepsin) activities of Chinese pond turtle during A. hydrophila infection. Microbiome analysis revealed that purslane increased the diversity of intestinal microbiota with a significant decrease in the proportion of potentially pathogenic bacteria (such as Citrobacter freundii, Eimeria praecox, and Salmonella enterica) and an increase in the abundance of probiotics (such as uncultured Lactobacillus). In conclusion, our study uncovers that purslane improves intestinal health to protect Chinese pond turtles against A. hydrophila infection.

Effects of Dietary Lysine Level on Growth Performance and Protein Metabolism in Juvenile Leopard Coral Grouper (Plectropomus leopardus).

An 8-week feeding trial was conducted to evaluate the effects of dietary lysine level on growth performance and protein metabolism of juvenile leopard coral grouper (Plectropomus leopardus) and thereby obtained the optimal dietary lysine requirement of P. leopardus. Six isoproteic and isolipidic experimental diets were formulated to contain 1.10%, 1.69%, 2.30%, 3.08%, 3.56%, and 4.36% lysine of diets, respectively. Each diet was assigned at random to triplicate groups of 25 juveniles (initial mean weight is 10.57 g) per tank in a flow-through mariculture system maintained at 27-30°C. Dietary inclusion of 2.30-3.08% lysine improved the weight gain rate (WGR) and specific growth rate and decreased the feed conversion ratio (FCR) of juveniles (P < 0.05). The intestinal digestive enzyme (trypsin, amylase, and lipase) activities were overall enhanced by dietary inclusion of 3.08-3.56% lysine (P < 0.05). The mammalian target of rapamycin (mTOR) signaling pathway was activated in fish fed diets with 1.69-2.30% lysine by upregulating the relative expression levels of hepatic TOR and S6K1 (p70 ribosomal protein S6 kinase 1) but downregulating the relative expression level of hepatic 4E-BP2 (eIF4E-binding protein 2). Conversely, the amino acid response signaling pathway was inhibited in fish fed diet with 2.30% lysine by downregulating the relative expression levels of hepatic GCN2 (general control nondepressible 2), ATF3 (activating transcription factor 3), ATF4a (activating transcription factor 4a), and ATF4b (activating transcription factor 4b). Additionally, dietary 1.69-3.08% lysine enhanced the plasma total protein level and hepatic lysine α-ketoglutarate reductase activity but depressed the blood urea nitrogen level and hepatic adenosine monophosphate deaminase activity (P < 0.05). Moreover, dietary 3.08% lysine increased the contents of whole-body crude protein and total amino acids, while 1.69%-4.36% lysine depressed the whole-body lipid content (P < 0.05). These results indicated that optimal dietary lysine increased the digestive enzyme activities, promoted protein synthesis but depressed protein degradation, and thereby improved the growth performance of P. leopardus. Based on the second-order polynomial model, the optimal lysine requirement of juvenile P. leopardus for WGR, FCR, and lysine deposition was 2.60%-2.97% of diets (4.91%-5.60% of dietary protein).

Effects of different diets on growth performance, digestive enzyme activities and intestinal bacterial community of juvenile Chinese giant salamander (Andrias davidianus)

This study analyzed the growth performance, digestive enzyme activities and intestinal microbial community in HC group (fed with Chironomid larvae), HH group (fed with Chironomid larvae plus Earthworms) and QY group (fed with Earthworms) of juvenile Chinese giant salamander (Andrias davidianus) after farming for 60 days. The results showed that diet can affect the growth performance, digestive enzyme activities and intestinal mcirobiota composition of juvenile Chinese giant salamander. The growth performance in juvenile Chinese giant salamander of HC group was significantly higher than that of HH group and QY group. The ether extract content in muscles of juvenile Chinese giant salamander of HH group and QY group was significantly lower than that of HC group. The intestinal digestive enzyme activities in juvenile Chinese giant salamander of HC group were significantly lower than that of HH group and QY group. The intestinal microbial richness and diversity in juvenile Chinese giant salamander of HH group and QY group were significantly higher than that of HC group. The most dominant phylum of HC group and HH group was Firmicutes but QY group was Bacteroidota, and the most dominant genus of HC group was Clostridium_sensu_stricto_1 but HH group and QY group was Bacteroides. The 24 specific bacterial groups with different classification levels had significant differences in three diet groups of juvenile Chinese giant salamander and these specific bacteria were concentrated in Firmicutes, Proteobacteria and Bacteroidota. Thus, the above studies indicated that Chironomid larvae as diet can increase the growth performance of juvenile Chinese giant salamander, while the addition of Earthworms as diet can enhance digestive ability and change microbiota composition in intestine of juvenile Chinese giant salamander.

Feed nutritional composition affects the intestinal microbiota and digestive enzyme activity of black soldier fly larvae.

Using black soldier fly larvae (BSFLs) to treat food waste is one of the most promising environmental protection technologies. We used high-throughput sequencing to study the effects of different nutritional compositions on the intestinal microbiota and digestive enzymes of BSF. Compared with standard feed (CK), high-protein feed (CAS), high-fat feed (OIL) and high-starch feed (STA) had different effects on the BSF intestinal microbiota. CAS significantly reduced the bacterial and fungal diversity in the BSF intestinal tract. At the genus level, CAS, OIL and STA decreased the Enterococcus abundance compared with CK, CAS increased the Lysinibacillus abundance, and OIL increased the Klebsiella, Acinetobacter and Bacillus abundances. Diutina, Issatchenkia and Candida were the dominant fungal genera in the BSFL gut. The relative abundance of Diutina in the CAS group was the highest, and that of Issatchenkia and Candida in the OIL group increased, while STA decreased the abundance of Diutina and increased that of Issatchenkia. The digestive enzyme activities differed among the four groups. The α-amylase, pepsin and lipase activities in the CK group were the highest, and those in the CAS group were the lowest or the second lowest. Correlation analysis of environmental factors showed a significant correlation between the intestinal microbiota composition and digestive enzyme activity, especially α-amylase activity, which was highly correlated with bacteria and fungi with high relative abundances. Moreover, the mortality rate of the CAS group was the highest, and that of the OIL group was the lowest. In summary, different nutritional compositions significantly affected the community structure of bacteria and fungi in the BSFL intestinal tract, affected digestive enzyme activity, and ultimately affected larval mortality. The high oil diet gave the best results in terms of growth, survival and intestinal microbiota diversity, although the digestive enzymes activities were not the highest.

Effect of Bacillus amyloliquefaciens LSG2-8 on the intestinal barrier function of Amur minnow (Rhynchocypris lagowskii).

Probiotics have been widely used in aquaculture. This article aims to study the effect of Bacillus amyloliquefaciens LSG2-8 on the intestinal barrier function of Rhynchocypris lagowskii. B. amyloliquefaciens LSG2-8 were added to R. lagowskii basal diets (CK) as additives at four concentrations: 1.0 × 106 (D-6), 1.0 × 107 (D-7), 1.0 × 108 (D-8) and 1.0 × 109 (D-9) CFU/g by dry weight of basal diet. After a 56 days feeding experiment, the intestinal digestive enzymes and immune enzymes activity of R. lagowski on group D-6, D-7, D-8 and D-9 diet were significantly higher than the control (P < 0.05). In molecular experiments, we found that the levels of TGF-β mRNA, IL-10 mRNA, ZO-1 mRNA and Claudin-3 mRNA in group D-8 R.. lagowskii were significantly higher (P < 0.05) than the control and other groups. Furthermore, the levels of IL-1β and IL-8 mRNA of R. lagowski on group D-6, D-7, D-8 and D-9 diet were significantly lower than the control (P < 0.05). In addition, we found that B. amyloliquefaciens LSG2-8 can regulate the intestinal flora balance and improve the intestinal structure of R. lagowskii. In conclusion, B. amyloliquefaciens LSG2-8 can improve the intestinal barrier function of R. lagowskii,and can be used as a feed additive in aquaculture.

Corrigendum: Effect of dietary soybean meal on growth performance, apparent digestibility, intestinal digestive enzyme activity and muscle growth-related gene expression of Litopenaeus vannamei

CORRECTION article Front. Mar. Sci., 12 May 2023Sec. Aquatic Physiology Volume 10 - 2023 | https://doi.org/10.3389/fmars.2023.1197207

Effects of cannabidiol on growth performance, appetite, antioxidant capacity and liver inflammatory gene expression of juvenile large yellow croaker (Larmichthys crocea) fed diets with high soybean oil level

This study evaluated the effects of cannabidiol (CBD) on growth performance, appetite, antioxidant capacity and liver inflammatory gene expression in juvenile large yellow croaker (Larmichthys crocea) fed diets with fish oil replaced by soybean oil. Six iso‑nitrogenous and isolipidic diets were formulated with fish oil (FO, the standard diet compared with the control only), soybean oil (SO, the control) and SO supplemented with 25, 50, 100 and 250 mg/kg CBD. After 9-week feeding, with the increase of CBD supplementation in SO diet, the growth performance (final body weight, specific growth rate and feed intake) and the intestinal digestive enzyme activities (amylase, lipase and trypsin) showed a significantly quadratic trend of variation and the maximum were observed in the fish fed SO diets with 100 mg/kg CBD. Correlation analysis showed that 100 mg/kg CBD supplemented in the SO diet could promote appetite of fish by inhibiting the mRNA expression of pro-opiomelanocortin in hypothalamus. The activities of aspartate transaminase and alanine transaminase and total protein level in the serum of fish showed a significantly quadratic trend with the supplementation of CBD increasing in SO diets, and the lower were observed in fish fed SO diets with CBD. Compared with the control, 25, 50, 100 and 250 mg/kg CBD supplemented in SO diets increased peroxidase activity and total antioxidant capacity and decreased malondialdehyde content in the liver of fish, and the highest superoxide dismutase activity was observed in fish fed SO diets with 100 mg/kg CBD. Moreover, fish fed SO diets with 100 and 250 mg/kg CBD had lower mRNA expression of tumor necrosis factor α, interleukin-1β, interleukin-6 and cyclooxygenase-2 in liver of fish compared with the control. In conclusion, 100 mg/kg CBD supplemented in diets with high SO level improved the growth performance and appetite in large yellow croaker. Simultaneously, the supplementation of 100 and 250 mg/kg CBD could promote antioxidant capacity and inhibit the inflammatory gene expression in liver of large yellow croaker fed diets with the high SO level. The optimal supplementation of CBD in diets with high SO level is recommended at 100 mg/kg for large yellow croaker.

Dietary hydrolyzable tannins reduce growth performance and induce histological damage of Chinese seabass (Lateolabrax maculatus)

Chinese seabass (Lateolabrax maculatus) is a popular carnivorous fish with delicious taste. Although the feed value of condensed tannins has been well documented for L. maculatus, information about the effects of hydrolyzable tannins (HTs) on the growth and health of L. maculatus is limited. This study was conducted to assess the effects of dietary HTs on growth performance, body composition, intestinal digestive enzyme activities, serum metabolites, antioxidant and immune response, and intestine and liver morphology of L. maculatus. A total of 640 fish were randomly divided into four groups with four replicates per group and 40 fish per replicate. Four diets were prepared to contain 0 (G0), 1 (G1), 2 (G2), and 4 (G4) g/kg of HTs. Fish were fed to apparent satiation twice a day during the 56-day feeding trial. Results showed that the final body weight, weight gain rate, specific growth rate, and feed intake were linearly decreased (p&amp;lt; 0.001) as dietary HTs increased. All fish had similar (p &amp;gt; 0.05) whole body compositions. Fish fed G2 and G4 had lower (p&amp;lt; 0.05) intestinal trypsin and lipase activities than those fed G0 and G1, whereas G4 had higher (p&amp;lt; 0.05) aspartate aminotransferase and alanine aminotransferase activities than G0. Serum total antioxidant capacity and lysozyme were linearly decreased (p&amp;lt; 0.01), but the malondialdehyde concentration was linearly increased (p&amp;lt; 0.01) as dietary HTs increased. Intestinal villi in G2 and G4 showed increased deformation, and the vacuolation of liver cells began to appear in G1 and was aggravated as dietary HTs increased. This study showed that HTs should be used with caution due to their growth-inhibiting effect, and the dietary HT level for L. maculatus is recommended to be less than 1 g/kg.

Effects of artificial diet breeding on intestinal microbial populations at the young stage of silkworm (Bombyx mori).

The silkworm (Bombyx mori) is an economically important insect and serves as a model organism for Lepidoptera. To investigate the effects of the intestinal microbial population on the growth and development of larvae fed an artificial diet (AD) during the young stages, we analyzed the characteristics of the intestinal microbial population using 16S rRNA gene sequencing technology. Our results revealed that the intestinal flora of the AD group tended to be simple by the 3rd-instar, which Lactobacillus accounting for 14.85% and leading to a decreased pH in the intestinal fluid. In contrast, the intestinal flora of silkworms in the mulberry leaf (ML) group showed continuous growth of diversity, with Proteobacteria accounting for 37.10%, Firmicutes accounting for 21.44%, and Actinobacteria accounting for 17.36%. Additionally, we detected the activity of intestinal digestive enzymes at different instars and found that the activity of digestive enzymes in the AD group increased by larval instar. Protease activity in the AD group was lower during the 1st- to 3rd-instars compared to the ML group, while α-amylase and lipase activities were significantly higher in the AD group during the 2nd- and 3rd-instar compared to the ML group. Furthermore, our experimental results indicated that changes in the intestinal population decreased the pH and affected the activity of proteases, which might contribute to the slower growth and development of larvae in the AD group. In summary, this study provides a reference for investigating the relationship between artificial diet and intestinal flora balance.

Effect of dietary bile acids supplementation on growth performance, feed utilization, intestinal digestive enzyme activity and fatty acid transporters gene expression in juvenile leopard coral grouper (Plectropomus leopardus)

This study aimed to evaluate the effects of dietary bile acids on growth performance, feed utilization, body composition, digestive enzyme activity, and related gene expression in juvenile leopard coral grouper (Plectropomus leopardus). Five diets with varying levels of dietary bile acids (0, 0.15, 0.3, 0.45 and 0.6%) were formulated and each diet was fed to triplicate groups of 15 fish (13.14 ± 0.14 g) for ten weeks. Results showed that the significant enhancement in weight gain (WG) and specific growth rate (SGR) was observed in fish fed 0.3% bile acids (P &amp;lt; 0.05). Additionally, feed conversion ratio (FCR) was significantly improved with bile acids inclusion (P &amp;lt; 0.05). Higher feed intake was also recorded in bile acids inclusion groups, and significantly up-regulated gene expression of hypothalamus neuropeptide Y (NPY) was found in 0.3% group compared with the control group (P &amp;lt; 0.05). Dietary bile acids (0.3%) significantly decreased lipid deposition in the whole-body (P &amp;lt; 0.05), and lower hepatosomatic index (HSI) and viscerosomatic index (VSI) were also found in this group. Moreover, intestinal trypsin and lipase activities were significantly increased in 0.3% group (P &amp;lt; 0.05) to promote feed digestion. In addition, the relative expression levels of intestinal fatty acid binding protein 2 (FABP2) significantly up-regulated with inclusion of dietary bile acids, suggesting an enhancement of fatty acid transport (P &amp;lt; 0.05). In contrast, cholesterol transport related genes NPC1 like intracellular cholesterol transporter 1 (NPC1L1) and CD36 were notably down-regulated as bile acids inclusion (P &amp;lt; 0.05). This study provides valuable information for the formulation of diets for juvenile coral trout and indicates that dietary bile acids could potentially be used to improve growth performance and feed utilization.

Effects of Replacement of Fish Meal with Poultry By-Product Meal (PBM) on Growth Performance, Digestive Enzyme, and Immunity of Giant River Prawn (Macrobrachium rosenbergii)

A 56-day feeding trial was performed to determine the effect of replacing fishmeal with 0, 25%, 50%, 75%, and 100% PBM (FM) on growth performance, digestive enzyme, and immunity of juvenile giant river prawn (Macrobrachium rosenbergii). Diets were fed in quadruplicate (50 prawns per replicate) to satiation (3–5% of their body weight). The finial weight, weight gain, and specific growth rate of prawns were significantly reduced P &lt; 0.05 when 100% PBM was substituted for fish meal, whereas the remaining test diets showed no variation compared to the control P &gt; 0.05 . There was no significant difference in survival rates. The moisture, crude protein, and crude fat of the prawn were unchanged P &gt; 0.05 . The SOD activity, MDA content, and AKP activity of hemolymph did not change significantly. However, the ACP activity of all replacement groups decreased significantly P &lt; 0.05 . The amylase enzyme activity in the intestine of prawn fed 25% of PBM increased significantly compared with the control group, while the trypsin and lipase activities were unchanged. This study showed that PBM up to 75% replacement group does not affect growth performance, and all replacement groups have no adverse effect on intestinal digestive enzyme activity and immunity in juvenile M. rosenbergii. Therefore, poultry by-product meal could replace fish meal by up to 75%.

Effects of Starvation and Refeeding on Growth, Digestion, Nonspecific Immunity and Lipid-Metabolism-Related Genes in Onychostoma macrolepis.

The present research was conducted to assess the influences of starvation and refeeding on growth, nonspecific immunity and lipid metabolic adaptation in Onychostoma macrolepis. To date, there have been no similar reports in O. macrolepis. The fish were randomly assigned into two groups: control group (continuous feeding for six weeks) and starved-refed group (starvation for three weeks and then refeeding for three weeks). After three weeks of starvation, the results showed that the body weight (BW, 1.44 g), condition factor (CF, 1.17%), visceral index (VSI, 3.96%), hepatopancreas index (HSI, 0.93%) and intraperitoneal fat index (IPFI, 0.70%) of fish were significantly lower compared to the control group (BW, 5.72 g; CF, 1.85%; VSI, 6.35%; HSI, 2.04%; IPFI, 1.92%) (p < 0.05). After starvation, the serum triglyceride (TG, 0.83 mmol/L), total cholesterol (T-GHOL, 1.15 mmol/L), high-density lipoprotein (HDL, 1.13 mmol/L) and low-density lipoprotein (LDL, 0.46 mmol/L) concentrations were significantly lower than those in the control group (TG, 1.69 mmol/L; T-GHOL, 1.86 mmol/L; HDL, 1.62 mmol/L; LDL, 0.63 mmol/L) (p < 0.05). The activities of intestinal digestive enzymes (amylase, lipase and protease) in the starved-refed group were significantly lower than those in the control group after three weeks of starvation (p < 0.05). The highest activities of immune enzymes such as lysozyme (LZM), acid phosphate (ACP), alkaline phosphate (ALP), superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) in the hepatopancreas were presented in the starved-refed group at second week, and significantly higher than those in the control group (p < 0.05). Meanwhile, starvation significantly improved intestinal immune enzymes activities (p < 0.05). the lowest TG contents and the highest expression levels of lipolysis genes including hormone-sensitive lipase (HSL) and carnitine palmitoyl transferase 1 isoform A (CPT-1A) appeared in the hepatopancreas, muscle and intraperitoneal fat after starvation, indicating the mobilization of fat reserves in these tissues (p < 0.05). After refeeding, the recovery of TG content might be mediated by the upregulation of the expression levels of lipogenesis genes such as sterol regulatory element binding protein 1 (SREBP1) and fatty acid synthase (FAS). Understanding the duration of physiological and metabolic changes in O. macrolepis and their reversibility or irreversibility to supplementary feeding response could provide valuable reference for the adaptability of O. macrolepis in large-scale culturing, proliferation and release.

Bacillus subtilis and Pichia farinose mixture improves growth performance and nutrient absorption capacity in broiler chicks.

This study evaluated the effects of dietary supplementation of Bacillus subtilis and Pichia farinose mixture (BPM) on growth performance, apparent ileal digestibility, cecal bacteria counts, small intestinal morphology and digestive enzymes activities, and jejunal nutrient transporters gene expression in broiler chicks. A total of 768 one-day-old Ross 308 broiler chicks were randomly Q18 assigned into 3 groups based on the initial body weight (42.00 ± 0.08 g). The experimental periods were 35 days. There were 16 replicates per group and 16 birds per cage. Dietary treatments included a basal diet supplemented with 0, 0.1, or 0.2% BPM to form CON, BPM0.1 (consisting Bacillus subtilis with 1.0 × 107 viable spore and Pichia farinose with 1.0 × 107 viable spore per kg diet), and BPM0.2 (consisting Bacillus subtilis with 2.0 × 107 viable spore and Pichia farinose with 2.0 × 107 viable spore per kg diet) groups. Dietary supplementation of graded levels of BPM has positive effects on growth performance of broiler chicks, manifesting in the increase of body weight gain during days 1-35 as well as the decrease of feed conversion ratio during days 1-7, 21-35, and 1-35. Moreover, BPM supplementation positively improved ileal energy and crude protein digestibility, increased Lactobacillus counts, optimized intestinal morphology, enhanced intestinal digestive enzymes activities, and upregulated jejunal SGLT-1, GLUT-2, and PEPT-1 expression. Therefore, BPM supplementation improved growth performance of broiler chicks, which was partially related to the improvement in intestinal nutrient absorption capacity.

Effects of Dietary Rare Earth Chitosan Chelate on Performance, Egg Quality, Immune and Antioxidant Capacity, and Intestinal Digestive Enzyme Activity of Laying Hens.

Rare earth chitosan chelate salt (RECC) is a potential feed additive and is a product of the chelation effect between rare earth ions and chitosan. This research study aims to explore the effects of dietary RECC on performance, egg quality, intestinal digestive function, and the immune and antioxidant capacity of laying hens in the late phase of production. A total of 360 56-week-old Dawu Jinfeng laying hens were randomly allotted into four treatment groups with six replicates per treatment and 15 birds per replicate. The laying hens were fed the basal diet supplemented with, respectively, 0 (control: CON), 100 (R1), 200 (R2), and 400 (R3) mg/kg for 8 weeks. Dietary RECC significantly improved average daily feed intake (ADFI) and average daily egg yield in both linear and quadratic manner (p < 0.05). In addition, albumen height and HU were improved significantly (p < 0.05) in a dose-dependent manner of RECC. In addition, a significant decrease (p < 0.05) in serum TP, IgA, and MDA for the R1 group and IgG in the R2 group were notable, while the increase in serum TP and decrease in T-AOC were found for R3 dietary group compared to CON (p < 0.05). The level of intestinal IL-2 and TNF-α was decreased by dietary RECC (p < 0.01). The activities of the digestive enzyme (α-Amylase, lipase, and Trypsin) showed a quadratic change with an increase and then decrease in response to increasing dose of RECC, 200 mg/kg RECC significantly increased the activity of lipase and Trypsin (p < 0.01). Supplementation of dietary RECC at low doses compared to higher doses impacted positive effects on the antioxidant capacity and immune function (p < 0.05). The utilization of RECC as a feed additive in the diet of aged laying hens exerted beneficial effects on egg production, albumen quality, humoral immunity, inflammatory response, and activity of digestive enzymes. Thus, the regulation of antioxidant capacity and duodenal function via increased enzyme activity and immune and inflammatory response were critical to the improvement of laying performance and egg quality in aged hens. The optimal supplemental dose is 100-200 mg/kg.

Triploidization modulates intestinal microbiota and promotes growth in Carassius auratus

Intestinal microbiota plays a key role in modulating host growth. However, the effect of triploidization on intestinal microflora and fast growth has not been fully explored. Here, autotriploid Carassius auratus (3nRR, 3n = 150) derived from Carassius auratus red var. (♀, RCC, 2n = 100) × autotetraploid fish (♂, 4nRR, 4n = 200) was established. Intestinal microbial community analysis of RCC and 3nRR was performed by 16S rRNA gene sequencing. Gut characteristics, growth rate, and digestive enzyme activity of the two groups of fish were explored. Significant changes in gut assemblages were observed in 3nRR fish. Differences in intestinal characteristics (structure, relative gut density, relative gut length, relative gut mass, and Zihler's index) were observed between RCC and 3nRR groups. Associations between microbial assemblages and intestinal characteristics were evaluated. Growth rate and activities of intestinal digestive enzymes (cellulase, amylase and trypsin) were higher in 3nRR compared with that in RCC. Spearman's correlation analysis showed a positive correlation between bacteria orders (Clostridiales, Micrococcales and Lactobacillales) and fast growth in 3nRR. In summary, the findings indicated that triploidization caused changes in gut microbiota and characteristics, and digestive enzyme activity. The relative abundance of several bacteria species was positively correlated with fast growth in 3nRR. The present study provided new insights into the growth mechanism of 3nRR and its interaction with intestinal microorganisms.

Intestinal response of Rana chensinensis larvae exposed to Cr and Pb, alone and in combination

Although numerous investigations on the adverse impact of Cr and Pb have been performed, studies on intestinal homeostasis in amphibians are limited. Here, single and combined effects of Cr (104 μg/L) and Pb (50 μg/L) on morphological and histological features, bacterial community, digestive enzymes activities, as well as transcriptomic profile of intestines in Rana chensinensis tadpoles were assessed. Significant decrease in the relative intestine length (intestine length/snout-to-vent length, IL/SVL) was observed after exposure to Pb and Cr/Pb mixture. Intestinal histology and digestive enzymes activities were altered in metal treatment groups. In addition, treatment groups showed significantly increased bacterial richness and diversity. Tadpoles in treatment groups were observed to have differential gut bacterial composition from controls, especially for the abundance of phylum Proteobacteria, Firmicutes, Verrucomicrobia, Actinobacteria, and Fusobacteria as well as genus Citrobacter, Anaerotruncus, Akkermansia, and Alpinimonas. Moreover, transcriptomic analysis showed that the transcript expression profiles of GPx and SOD isoforms responded differently to Cr and/or Pb exposure. Besides, transcriptional activation of pro-apoptotic and glycolysis-related genes, such as Bax, Apaf 1, Caspase 3, PK, PGK, TPI, and GPI were detected in all treatment groups but downregulation of Bcl2 in Pb and Cr/Pb mixture groups. Collectively, these results suggested that Cr and Pb exposure at environmental relevant concentration, alone and in combination, could disrupt intestinal homeostasis of R. chensinensis tadpoles.

Effects of dietary artemisinin on growth performance, digestive enzyme activity, intestinal microbiota, antioxidant capacity and immune biomarkers of Coral trout (Plectropomus leopardus)

Artemisinin is an active ingredient extracted from the Chinese medicine Artemisia carvifolia. The experiment investigated the effects of dietary artemisinin on growth performance, intestinal digestive enzyme activity and flora, antioxidant capacity, immune-related gene expression of Coral trout (Plectropomus leopardus). The 450 fish with an initial weight of 9.40 ± 0.04 g were randomly divided into 5 groups of 3 replicates and fed in 500 m3 fiberglass tank for 9 weeks. Five iso-nitrogenous (50% crude protein) and iso-lipidic (10% crude lipid) diets were formulated by supplementing various mass fractions of artemisinin (C0 0% as control; C0.2 0.20%, C0.4 0.40%, C0.8 0.80%, and C1.2 1.20%). The results showed that the C0.2 had the highest weight gain rate (WGR) compared to the others (P < 0.05). The levels of trypsin, amylase and lipase in the fish intestine reached their maximum values at C0.2 (P < 0.05). Compared to C0, feed supplementation with artemisinin significantly enhanced total antioxidant capacity in liver, intestine and serum, increased peroxidase, glutathione peroxidase, catalase and superoxide dismutase enzyme activities, and decreased malondialdehyde levels. The results of liver immune gene expression showed that tumor necrosis factor (TNFα), C-type lectin structural domain family 4 member M, myeloid differentiation factor 88 genes were significantly downregulated in the C0.8 group compared with the control group (P < 0.05). Analysis of the intestinal flora of C0, C0.2 and C1.2 showed that the supplementation of artemisinin reduced the relative abundance of conditionally pathogenic bacteria (Vibrio). In summary, dietary supplementation with artemisinin improved growth performance, enhanced nonspecific immunity and reduced the relative abundance of harmful flora in intestinal tract of Coral trout. Based on the quadratic regression analysis of WGR and dietary artemisinin levels, the recommended level of artemisinin supplements in the diet of Coral trout is 0.38%.

Effects of different probiotics (Bacillus subtilis) addition strategies on a culture of Litopenaeus vannamei in biofloc technology (BFT) aquaculture system

Augmenting biofloc systems with probiotics have been proven to improve water quality and enhance fish/shrimp performance. In this study, we aimed to evaluate the effects of different B. subtilis addition strategies in biofloc systems on water quality, Litopenaeus vannamei (L. vannamei) growth performance, and immune enzymes. Two probiotics addition methods were explored: addition to water group (A), addition via the aquafeed (B), and the control (C), in which no probiotics were applied. No significant differences were found in the means of NO2−-N between groups B and C, but both were significantly lower (p < 0.05) in NO2−-N than in group A (0.55 ± 0.12 mg/L). The mean NO3−-N concentration for group C (41.37 ± 2.45 mg/L) was the highest and the lowest for group A (37.84 ± 1.99 mg/L), among all treatments. The different addition methods did not influence the growth parameters of L. vannamei, except for the survival rate (SR), in which group A recorded the highest SR (93 ± 0.2%) (p < 0.05). It was found that irrespective of the addition strategy (groups A (5.35 ± 0.04 U/mgprot) and B (5.63 ± 0.06 U/mgprot)), probiotics application resulted in a significant increase in the intestinal pepsin of L. vannamei. The activity of catalase (CAT) and total antioxidant capacity (T-AOC) in the hepatopancreas were dependent on the addition method. However, SOD, ACP, and other immune parameters were independent of the addition method. The addition of Bacillus subtilis to the experimental system did not achieve a considerable growth effect of the growth performance of L. vannamei in BFT systems. Considering the two addition strategies, adding probiotics B. subtilis via the aquafeed was suggested, based on the corresponding effects on water quality, intestinal digestive enzyme activity, and non-specific immune enzymes activities of the shrimp.

Improvement of Flesh Quality of Farmed Silver Carp (Hypophthalmichthys molitrix) by Short-Term Stocked in Natural Water

To investigate the effects of different raising environments on the flesh quality, the study set up three groups of silver carp (Hypophthalmichthys molitrix), that is, pond-farmed; short-term stocked; and ranched, grown in a natural water ranch. This study compared the differences in muscle proximate composition and amino acid composition among three groups. The results showed that there was no difference between the ranched and the stocked groups in content of crude protein, ash, total amino acids (TAA), essential amino acids (EAA), and umami-flavored amino acids (UAA), with both groups being significantly higher than the farmed group. This shows that, in terms of flesh quality, the stocked group was closer to the ranched group and better than the farmed group after being stocked in natural water for 30 days. The results suggest that the flesh quality of farmed fish was improved by short-term stocking in natural water. To elucidate the reasons of flesh quality change in the stocked group, this study compared the food composition and intestinal digestive enzyme activity in three groups, demonstrating that the ranched and stocked groups had similar food composition, with their detritus proportion lower than that of the farmed group, consuming easily digestible phytoplankton diatoms rich in amino acids and fatty acids. No significant difference was seen between the ranched group and the stocked group, for which amylase, lipase, and trypsin activities were lower than that of the farmed group. It is hypothesized that differences in environmental and food composition resulted in lower digestive enzyme activity in the ranched group and the stocked group. In summary, the short-term stocking of farmed fish in a natural water ranch can effectively improve the nutrient content, quality and flavor, and promote value of fish products.