Abstract:Carnivorous fish have a very limited ability to use carbohydrates, and excessive carbohydrate will lead to the disorder of sugar metabolism and the decline of immune function, thus inhibiting the growth of fish. Starch as a cheap energy and adhesive in feed, appropriate addition can save protein and reduce feed cost. In order to evaluate the effects of starch structure on intestinal health of Micropterus salmoides, two isonitrogenous and lipid experimental diets were fed with 10% common corn starch (CS) and high amylose corn starch (HACS), respectively. M. salmoides with an initial weight of (8.53±0.06) g were fed for 8 weeks in an indoor system. The results showed that specific growth rate (SGR) and protein efficiency rate (PER) of M. salmoides in HACS group were significantly higher than those in CS group. Meanwhile, the intestinal catalase (CAT) and total superoxide dismutase (T-SOD) activities in HACS group were significantly higher than those in CS group, and the expressions of antioxidant related genes nrf2 and cat were significantly up-regulated. Moreover, compared with CS group, the relative expression levels of pro-inflammatory cytokines (TNF-α and IL-8) in HACS group were significantly down-regulated, while the relative expression levels of anti-inflammatory cytokines (TGF-β) were significantly up-regulated. At the same time, it was observed that the abundance of Cyanobacteria and Lactobacillus in HACS group was significantly increased at phylum level and genus level. It reduced the abundance of potentially harmful bacteria (Acinetobacter, Kocuria). Further phenotypic prediction showed that compared with common corn starch, feeding high amylose corn starch could significantly reduce the proportion of Gram-negative bacteria, increase the proportion of gram-positive bacteria, and significantly reduce the abundance of potential pathogenic bacteria. In conclusion, high amylose maize starch can effectively improve intestinal morphology, antioxidant capacity and immune level, and improve intestinal microflora structure and function of largemouth bass. Therefore, high amylose can improve the intestinal health of M. salmoides.

Abstract:Coenzyme residue (CR) is a by-product of the production of coenzyme Q10. It is mainly obtained by fermentation products of Rhodobacter sphaeroides, glucose, and corn steep liquor. At present, it has been approved as a feed material for aquaculture of aquatic animals in China. To explore the effect of CR replacing fish meal in the compound feed of juvenile Chinese mitten crab (Eriocheir sinensis) on the growth performance, health and intestinal flora, juvenile crabs (0.70 ±0.01 g) were fed in an 8-week feeding trial. On the basis of 20% fish meal level(control group), CR was used to replace 20%, 40%, 60%, 80%, 100% fish meal in the feed (recorded as C, T20, T40, T60, T80, T100). The results showed that, compared with C, the growth performance of T40 had no significant change, and the crude protein content of muscle in T60 was significantly reduced. The growth performance, body crude protein and crude fat content of T80 and T100 were significantly reduced; Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AKP), triglyceride (TG) showed no significant difference among the groups. Total protein (TP) level was significantly decreased in T100. Serum glucose (Glu) was significantly decreased in the replacement groups. The serum levels of total cholesterol (T-CHO) and high-density lipoprotein cholesterol (HDL-C) in T60, T80 and T100 were significantly decreased, and the levels of low-density lipoprotein cholesterol (LDL-C) in T80 and T100 were significantly decreased. Compared with C, there was no significant difference in the activity of hepatopancreas superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activity increased significantly. The content of malondialdehyde (MDA) decreased significantly in T100. Alpha diversity index showed no significant difference among three treatments (C, T40, T80). Principal coordinate analysis (PCoA) suggested that the microbial community structure in T80 group changed compared with the C group. In conclusion, CR can replace 40% fish meal in the feed of juvenile Eriocheir sinensis without affecting growth performance, antioxidant capacity and intestinal flora. When the replacement level reaches 80%, the growth performance and accumulation of nutrients of crab will be limited, and intestinal microbiota also changed. This experiment provides a theoretical reference for the application of CR in aquatic animal feed.

Abstract:The study investigated the effects of dietary supplementation of sodium butyrate on growth performance, intestinal digestive enzyme activity, serum biochemical indices and intestinal morphology of Ctenopharyngodon idella. Based on the control diet (SB0), microencapsulated sodium butyrate (containing 50% sodium butyrate) was added at the levels of 0 mg/kg (SB0), 1 000 mg/kg (SB1), 2 000 mg/kg (SB2) and 3 000 mg/kg (SB3) to form four iso-nitrogenous and iso-lipidic diets, respectively. A total of 300 C. idella juvenile (10.0±0.1) g were randomly divided into 4 groups with 3 replicates (cages) and 25 fish per replicate. The fish were fed the four diets in indoor cement ponds for 8 weeks. The results showed that the weight gain and feed conversion ratio of all groups were 273.7%-279.9%, 1.55-1.60, and dietary sodium butyrate did not significantly affect the growth performance and body composition of C. idella (P>0.05). Compared to the control group (SB0), dietary sodium butyrate significantly increased intestinal protease activity and serum superoxide dismutase (SOD) activity (P<0.05), and decreased serum aspartate aminotransferase (AST) activity (P<0.05). In addition, serum alkaline phosphatase (AKP) activity was increased significantly in SB1 group (P<0.05), while serum alanine aminotransferase (ALT) activity was decreased significantly in SB2 and SB3 groups (P<0.05). There was no significant difference in intestinal amylase activity, serum acid phosphatase (ACP), triglyceride (TG), glucose (GLU), total protein (TP) and D-lactic acid (D-LA) among the four groups (P>0.05). In intestinal and hepatic histology, the supplementation of sodium butyrate significantly increased the height of intestinal villi (P<0.05), and the thickness of muscle layer in SB1 and SB2 groups was significantly higher than that in the control group (P<0.05), but no significant differences in intestinal villus width and hepatic histology were observed among the four groups (P>0.05). In conclusion, dietary supplementation of sodium butyrate did not significantly promote the growth performance of C. idella, but increased the activity of intestinal digestive enzymes and improved the morphology of intestinal tissue.

Abstract:At present, there are still some problems in the cultivation of aquatic fry in the market, such as the low survival rate caused by the inappropriateness of food. Therefore, it is particularly important to meet the nutritional needs of fish larvae at the stage of breeding high-quality fry. The purpose of this study was to investigate the effects of feeding selenium-enriched yeast on growth, survival rate, fatty acid composition, liver and intestinal structure, and stress resistance of Micropterus salmoides larvae. The five selenium supplementation concentrations of 0 (Y-se0), 5 (Y-se5), 10 (Y-se10), 15 (Y-se15) and 20 (Y-se20) mg/L were set to enhance the selenium nutrition of the M. salmoides larvae, and the enhanced selenium larvae were fed to 3000 M. salmoides larvae in glass tank (2.1 mg/ind., 200 ind./tank) for 20 days. At the end of the feeding experiment, 10 larvae per tank were placed in the 35 ℃ thermostatic water bath for acute temperature stress test. The results showed as follows: ① The survival rate (78.67%±1.55%), final body weight (49.28±1.56) mg, body length (1.35±0.05) cm and specific growth rate (15.78±0.16) of the Y-se15 group were significantly higher than those of the control group (P<0.05), but there were no significant differences in the condition factor (CF) among all groups (P>0.05). ② EPA content in the Y-se5 group was significantly lower than that of the control group (P>0.05); the DHA/EPA value of Y-se5 and Y-se15 groups were significantly higher than that of the control group (P<0.05). ③ The catalase (CAT) activity in the liver of Y-se10, Y-se15 and Y-se20 groups were significantly higher than that of the control group (P<0.05), and the glutathione peroxidase (GSH-Px) activity in the liver of all treatment groups were significantly higher than that of the control group (P<0.05). However, the content of malondialdehyde (MDA) in the liver of Y-se10, Y-se15 and Y-se20 groups were significantly lower than that of the control group (P<0.05), and the activity of total superoxide dismutase (T-SOD) exhibited no significant difference between all the treatment groups with the control group (P>0.05). ④ The vacuolation of liver tissue in the Y-se15 group was much less, and the intestinal villus length in the selenium yeast supplemental groups were significantly higher than that of the control group (P<0.05). ⑤ Under the 35 ℃ stress condition, the survival time of the Y-se15 group was significantly higher than that of the control group (P<0.05). In conclusion, the supplementation of selenium yeast at 15 mg/L level could significantly increase the growth, survival rate and DHA/EPA level of M. salmoides larvae, and improve the health status of fish by the enhancement of the organism's antioxidant and anti-stress ability. This study preliminarily explored the effect of feeding artemia nauplii with enriched yeast selenium on M. salmoides larvae, with the aim of providing reference for further improving the technology of nutrient fortification in the open-mouth diet of aquatic animal seedlings and promoting the high-quality development of aquaculture.

Abstract:Animal protein is an indispensable source in the feed of carnivorous fish. Fish meal, as a high-quality animal protein, has high price and limited source due to the adverse impact of resources, storage and recent international situation. Because of its rich nutritional value, high digestibility, balanced amino acids and high biological conversion rate, poultry by-product meal has attracted much attention from the animal protein source production market. Therefore, the application effect of poultry by-product meal in the feed of Micropterus salmoides was systematically evaluated in order to understand the quality and safety of domestic poultry by-product meal, and to provide a theoretical basis for rational use of meat meal. To evaluate the feasibility of replacing fish meal with poultry by-product meal, five isonitrogen-isolipid experimental diets (control, PBM 12.5, PBM 25.0, PBM 37.5, PBM 50.0) were formulated. M. salmoides [initial body weight (9.25±0.13) g] was fed the system for 8 weeks. The results showed that there was no significant difference in the weight gain rate(WGR) , specific growth rate (SGR) and feeding ratio(FR) of each group during the breeding period of M. salmoides. Compared with the control group, the activities of total superoxide dismutase (T-SOD) and catalase (CAT) of all experimental groups in liver were significantly increased, while the content of malondialdehyde (MDA) was significantly decreased. With the increase of replacement level, the relative expression levels of anti-inflammatory cytokines (IL-10, TGF-β) in liver were significantly up-regulated, while the relative expression levels of pro-inflammatory cytokines (IL-8, TNF-α) were significantly down-regulated, but had no significant effect on the clinical symptoms of liver tissue structure. In addition, with the increase of replacement level, the relative expression levels of intestinal antioxidant genes (sod and cat) and intestinal tight junction protein genes (Occludin, ZO-1 and Claudin-1) were significantly up-regulated, while the contents of D-lactate (D-lac) and lipopolaccharide (LPS) in serum were significantly decreased. In conclusion, replacing 50% fish meal with poultry by-product meal in the basal diet (40% fish meal) did not inhibit the growth of largemouth bass, but also it can enhance the antioxidant capacity and immunity of fish, and improve the liver and intestinal health of M. salmoides. Therefore, poultry by-product meal can be used as a high quality protein source for M. salmoides feed.

Abstract:Grass carp (Ctenopharyngodon idella) were fed with basic feed (control group), basic feed supplemented with enrofloxacin or florfenicol for two weeks, respectively. Thereafter, enzyme activity, real time quantitative PCR (qRT-PCR), and high-throughput sequencing were used to analyze the effects of these two antimicrobials on the intestinal oxidative stress, immunity and intestinal microflora of C. idella. The results showed that, (1) additions of enrofloxacin and florfenicol could reduce the content of glutathione peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) in the intestines of C. idella, while they increased the amount of malondialdehyde (MDA), resulting in oxidative stress in the intestines of C. idella. (2) In the florfenicol group, the mRNA expressions of immune related factors, including TNF-α, IL-1β, IL-12, NF-κB-p65, sIgM and intestinal mucosa-related protein ZO-1, ZO-2, occludin, CLDN-1 and JAM3 were significantly lower than those in the control group. In the enrofloxacin group, the mRNA expressions of immune related factor, including TNF-α, IL-1 β, IL-12, TLR4, MHC Ⅱ and intestinal mucosa-related protein ZO-2, occludin, CLDN-1 and JAM3 were significantly lower than those in the control group. (3) The results of high throughput 16S rRNA sequencing showed that the additions of antimicrobials had no significant effects on α diversity (P > 0.05) of microflora in C. idella intestine. However, there were significant changes in β diversity (P < 0.05). The results showed that neither of the two antibiotics affected the community richness, but they changed the diversity among the sample communities. Taken together, dietary enrofloxacin and florfenicol could cause oxidative stress, inhibit the intestinal immunity as well as affect the intestinal microflora of C. idella. This study provides a reference for the researches related to the prevention and control of C. idella diseases and the green and healthy culture of C. idella.

Abstract:Bullfrog (Lithobates catesbeiana) tadpole culture technology is still in a vulnerable stage, and metamorphosis rate is an important index of L. catesbeiana tadpole culture. Traditional empirical feeding strategy may lead to insufficient or excessive feeding of L. catesbeiana tadpoles, affecting the digestion and absorption of nutrients and the development of internal organs. Eventually, it leads to slow growth and development, light weight after metamorphosis, poor immunity and it is easy to corrupt water body and cause other problems. The feeding strategy has a significant effect on the growth and development of tadpoles, but no scientific feeding standard has been established. Therefore, four feeding frequencies (1, 2, 3, 4 times/d) and four feeding levels (4%, 6%, 8% and 10%) were set to feed L. catesbeiana tadpoles to explore the appropriate feeding strategy for tadpoles. The feeding frequency experiment showed that the metamorphosis rate of tadpoles fed 3 times/d or 4 times/d was significantly higher than that of tadpoles fed once or twice/d, and the weight gain rate of 3 times/d was the highest (P>0.05). The metamorphosis to feeding ratio (MFR) increased with the increase of feeding frequency and was significantly higher for 2, 3, and 4 times/d than once/d. Feeding frequency had no significant effects on liver structure and intestinal protease, lipase, and amylase activities of froglets. The feeding level experiment showed that the metamorphosis rate increased with the feeding level increasing, and the average weight of metamorphosed tadpoles in 8% and 10% groups was significantly higher than that in 4% and 6% groups, but the intestinal protease activity of metamorphosed tadpoles decreased with the feeding level increasing. The content of lipid droplets in hepatocytes of metamorphosis tadpoles increased significantly in 8% and 10% groups, and fat deposition was obvious. The feeding level of 8% increased the relative abundance of Caldilinea (Chloroflexi) and Cetobacterium (Fusobacterium), and improved the intestinal microbial structure to a certain extent. In conclusion, it is recommended to feed L. catesbeiana tadpoles 3 times a day at a feeding level of 8%. Research on the scientific feeding strategy of L. catesbeiana tadpoles can improve the L. catesbeiana research system and increase the production efficiency of L. catesbeiana.

Abstract:In order to compare the effects of formula feed and forage fish (Xiangyun crucian carp) on the growth, digestive system structure and function, plasma biochemical indices and muscle quality of Siniperca chuatsi, 210 S. chuatsi with the initial body weight of (112.33±1.14) g were selected and randomly divided into 2 treatments, feeding complex diet and Xiangyun crucian carp respectively for 68 days. The results show that: ① The nutrient deposition rate of the feed group was significantly higher than that of the Xiangyun crucian carp, and the weight gain rate (WGR) and dry matter feed efficiency (FE) significantly increased by 23.14% and 30.53%, respectively, while the dry matter intake (FI) of the S. chuatsi in the feed group was not significantly different from that in the Xiangyun crucian carp. ② The muscle fibers of the back muscle of S. chuatsi in the feed group were finer. The muscle hardness, brittleness, chewiness and adhesion of S. chuatsi group were significantly better than those of Triploid crucian carp group, and the pH reduction value, drip loss and freezing exudation rate were decreased by 26.67%, 26.65% and 24.90%, respectively. The content of malonaldehyde (MDA) in vitro was significantly lower than that of Xiangyun crucian carp group. ③ The content of TG, TC and GLU of S. chuatsi plasma in feed group were significantly higher than those in Triploid crucian carp, while the MDA content was on the contrary . There were no significant differences in the contents of HDL-C, LDL-C and HDL-C/LDL-C between the two groups. ④ The activities of pepsin, amylase, lipase and trypsin in anterior, middle and posterior intestine of S. chuatsi in feed group were significantly higher than those in Xiangyun crucian carp. ⑤ Simpson index and Shannon index of intestinal microflora in the feed group were significantly 46.03% and 125.00% higher than those in the Xiangyun crucian carp group, and the abundance of Bacillus was increased. In conclusion, under the conditions of this experiment, S. chuatsi fed with compound feed have more advantages in growth rate, muscle quality, non-specific immune capacity and gastrointestinal development than fish fed with feed. This experiment provides a theoretical basis for S. chuatsi compound feed to replace traditional diet for fish breeding.

Abstract:(Objective) Taking loach as the research object, the effects of different concentrations of chlorogenic acid added to the feed on the growth performance, digestive enzyme activity, immune function and antioxidant capacity of loach were studied. (Method) Disease free and injury free loach, weighing 3.50 ±0.01g/tail, was randomly divided into 5 groups. The basic feed was supplemented with 0, 200, 400, 600 and 800 mg/kg chlorogenic acid test feed, and each group was repeated for 56 days. After feeding test, the growth performance, digestive enzyme activity, biochemical indicators, immune function and antioxidant capacity of loach (Misgurnus anguillicaudatus) were determined. (Results) Compared with the control group, the final weight (FBW), weight gain rate (WGR) and specific growth rate (SGR) of loach were significantly increased by adding chlorogenic acid to the diet (P < 0.05); The activities of protease, lipase and amylase in liver and intestine increased significantly (P < 0.05), total antioxidant capacity (T-AOC), catalase (CAT), superoxide dismutase (SOD), glutathione (GSH) and glutathione peroxidase (GSH-Px) increased significantly, and malondialdehyde (MDA) production decreased. The activities of aspartic acid transaminase (AST) and alanine transaminase (ALT) in liver increased with the increase of chlorogenic acid concentration, reaching the maximum at 400 mg/kg and 600 mg/kg respectively. With the increase of acid concentration, serum AST and ALT activities decreased significantly (P < 0.05), and serum lactate dehydrogenase (LDH) gradually decreased with the increase of chlorogenic acid concentration, reaching the lowest value at 400 mg/kg concentration; The content of complement 3 (C3) and complement 4 (C4) in serum increased first and then decreased, reaching the peak when the concentration of chlorogenic acid was 400 mg/kg and 600 mg/kg, respectively; the level of immunoglobulin M (IgM) in serum significantly increased (P < 0.05), reaching its maximum at a concentration of 600 mg/kg; serum lysozyme (LYS) content first increased and then decreased, reaching the maximum when the concentration was 400 mg/kg. (Conclusion) Adding 400,600 mg/kg chlorogenic acid to the diet can improve the antioxidant capacity of loach, significantly improve the growth performance and digestive enzyme activity of loach (P < 0.05), enhance the immune function of loach and the digestion and absorption of nutrients, and further protect the liver tissue of loach.

Abstract:In order to explore the effects of sea buckthorn (Hippophae rhamnoides) powder on growth, antioxidant ability and non-specific immunity of Yellow River carp (Cyprinus carpio haematopterus), a total of 450 C. carpio haematopterus with similar body weight about 7.55 g were randomly divided into five groups: control, HG, G-LSP, G-MSP, G-HSP, respectively. A 10-week feeding trial was performed. The results indicated that the weight gain rate of C. carpio haematopterus in G-HSP group was significantly higher than that in HG group. Compared with the control group, the content of malondialdehyde (MDA) in serum and hepatopancreas increased, but the activity of (CAT), superoxide dismutase (SOD) and total antioxidant activity (T-AOC) in serum and hepatopancreas decreased. These negative effects could be relieved with sea buckthorn powder supplementation. The high-carbohydrate diet inhibited nrf2 mRNA levels of hepatopancreas and muscle, while the mRNA levels of keap1 were promoted. Sea buckthorn powder significantly inhibited the decrease of nrf2 mRNA levels and increase of keap1 mRNA levels induced by the HG diet. And the antioxidant-related genes (gr, cat, gpx and sod) mRNA levels were also promoted by sea buckthorn powder. Moreover, fish fed the diet containing 0.5% sea buckthorn powder had higher activity of alkaline phosphatase (AKP), acid phosphatase (ACP), lysozyme (LZM) and the content of albumin (Alb) in serum, spleen and intestine. In addition, sea buckthorn powder can restore the abnormal mRNA expression of nf-κb, il-1β and tnf-α in spleen and intestine caused by high-carbohydrate diet. In conclusion, sea buckthorn powder can alleviate oxidative stress and inflammation injury caused by high-carbohydrate diet, and improve the growth performance, and enhance antioxidant ability and non-specific immunity of C. carpio haematopterus. The recommended dosage of sea buckthorn powder in diet is 0.5%.

Abstract:To determine the effects of growth and metabolism on carbon stable isotope turnover rates and fractionation factor of juvenile Eriocheir sinensis and different tissues, the hepatopancreas, muscle and gill tissues of juvenile E. sinensis in EA group [(4.0 g ±0.5) g] and EB group [(15.5 g ±0.5) g] were collected at 0, 7, 14, 21 and 28 days, respectively, in an aquarium of 0.2×0.2×0.3 m. The turnover process of stable carbon isotopes was investigated, and the fractionation factor of stable carbon and nitrogen isotopes were determined. The results showed that (1) The turnover rate of carbon stable isotopes in EA group was greater than that in EB group, and the turnover rate decreased with the increase of juvenile crab size. (2) The turnover rate of hepatopancreas was the fastest, followed by muscle and gills. The half-lives of hepatopancreas, muscle and gills in EA group were 20.88, 29.37 and 34.14 days, respectively, and those in EB group were 21.73, 35.18 and 66.01 days, respectively. (3) Metabolism was more principal for driving the turnover of carbon stable isotope with the contribution ranging from 79.82% to 94.04% for hepatopancreas, from 67.00% to 81.90% for gills, and from 71.61% to 90.36% for muscle. (4) The fractionation factors of carbon and nitrogen stable isotopes were 0.98‰ ±0.19‰ and 3.01‰ ±0.02‰, respectively. This study not only provided a reference for the nutritional ecology of juvenile E. sinensis, but also provided a scientific basis for bait selection in the breeding process of E. sinensis.

Abstract:This study was conducted to investigate the regulation mechanism of dietary lysine (Lys) content in Litopenaeus vannamei after partially replacing fish meal with fermented soybean meal, where 0%, 0.25%, 0.50%, 0.75% and 1.00% of crystalline lysine was added to the basic feed (recorded as Lys0, Lys25, Lys50, Lys75 and Lys100). Litopenaeus vannamei with an initial body weight of (2.0±0.1) g were selected for a 56-day feeding trial in an indoor cement pond fed with above 5 isonitrogenous and iso-lipidic experimental diets respectively, and those in Lys0 and Lys75 groups under went metabolomics and transcriptomic analysis based on significantly different growth performance, crude protein and lipid content in muscle, hepatopancreas health as well(P<0.05). The results showed that compared to Lys0 group, a total of 28 different metabolites were detected in Lys75 group, among which 2 metabolites were down-regulated and 26 metabolites were up-regulated; Signal pathway analysis was performed on 7 different metabolites annotated to the KEGG database, and 4 important metabolic pathways were screened out, namely glycine, serine and threonine metabolism, arachidonic acid metabolism, Sphingolipid metabolism, glycerophospholipid metabolism. In the Lys75 group, choline was significantly down-regulated in the hepatopancreas(P<0.05), the expression of γ-butyl betaine plus dioxygenase genes was significantly up-regulated(P<0.05), and the expressions of hexokinase genes and acetylcholinesterase genes were significantly down-regulated(P<0.05). The results indicated the increase of dietary lysine level due to crystal lysine addition helped the β-oxidation of fatty acids in the hepatopancreas, playing a role in protein saving and protecting the health of the hepatopancreas as well, thus promoted the growth of the shrimp.

Abstract:This experiment was performed to investigate the effects of soybean meal on intestinal health of Songpu Mirror carp (Cyprinus carpio Songpu) as well as the mechanism of AKG alleviating intestinal injury. A total of 609 juvenile Songpu mirror carp with an initial body weight of (9.51±0.06) g were randomly divided into 7 groups with 3 replicates per group and 29 fish per group. The control group was fed with 30.8 % fish meal (FM group) as the protein source. The experimental group was fed with 40 % soybean meal (SM group) as basic diet. The AKG group were fed with the basic diet supplemented with 1% α-ketoglutarate. Groups Met and Com were fed with the basic diet supplemented with 300 mg/kg Metformin and 0.2 mg/kg Compound C respectively. Groups Met+AKG and Com+AKG were supplemented with Metformin and Compound C on the basis of AKG group respectively. The experiment lasted for 59 days. Compared with FM group, mucosa ATP and ADP contents of the distal intestine (DI) were significantly increased (P<0.05) in SM group. Meanwhile, the expression of ACC, tumor necrosis factor alfa (TNF-α), interleukin-1 beta (IL-1β), transforming growth factor-beta (TGFβ2), caspase9, Claudin7, Claudin11, Claudin3c, Occludin in the proximal intestine (PI), the expression of AMP-activated protein kinase alfa (AMPK-α), target of rapamycin (TOR), ACC, IL-1β, TGFβ1, Caspase8, Claudin7, Occludin in the mid intestine (MI), the expression of TGFβ1, caspase8, caspase9 in the DI were significantly decreased and the expression of TNF-a, Claudin11, Claudin3c, Occludin in the DI were significantly increased (P<0.05) in SM. Compared with SM, the expression of TGFβ1 (PI), Claudin7 (PI), Claudin11 (PI, MI and DI), TOR (PI and MI), caspase8(MI), TNF-α (MI) and Occludin (DI) were significantly decreased (P<0.05) in AKG group. The ADP and AMP contents of mucosa of DI were significantly increased in Met and Com group. Subsequently, the expression of AMPK-α (PI), TOR (MI and DI), TNF-α (PI), IL-1β (PI), Caspase9 (PI), Claudin7 (PI), Claudin11 (PI and MI), Claudin3c (PI), TGFβ1 (MI) were significantly increased and the expression of Occludin were significantly decreased in Met group. The expression of Occludin (PI) were significantly increased and the expression of Claudin11(MI and DI) and Occludin (DI) were significantly decreased in Com group. Compared with AKG, the ATP, ADP and AMP contents of mucosa of DI were significantly increased in Com+AKG group. The ADP contents of mucosa of DI were significantly increased in Met+AKG group. The expression of Claudin7 (PI), Claudin11(PI) and TOR (MI) were significantly decreased in Met+AKG and Com+AKG. Morever, the expression of caspase8 (PI), Claudin11 (MI) and Claudin7(DI) were significantly increased in Met+AKG. The expression of Claudin11 (DI) and Occludin (DI) were significantly increased in Com+AKG (P<0.05). In conclusion, soybean meal decreased the energy level of PI and MI, but inhibited the expression of AMPK-α, TOR and ACC, and further decreased the expression of tight junction protein in PI and MI. Intestinal inflammation in DI was triggered. AKG can improve the expression of TOR, tight junction and anti-inflammatory factors in PI, reduce the expression of pro-inflammatory factors in MI and DI, alleviate the apoptosis of MI and DI by inhibiting endogenous apoptosis, and alleviate the damage of soybean meal to the intestine of carp. This study found the way that soy protein would damage intestinal health, and its effect on intestinal mucosal energy metabolism and the mechanism of AKG in alleviating intestinal injury. So this may provide a theoretical basis for improving the application of soybean in aquatic animal production.

Abstract:This experiment aims to study the effect of vitamin C on the growth performance of Andrias davidianus and the structure and function of various organs in the digestive system. Using fish meal, chicken meal, etc. as the protein source and fish oil as the fat source to prepare A. davidianus basal feed, the basal feed was added with 0, 150, 300, 450, 600 and 750 mg/kg of vitamin C (vitamin C phosphate 35% content), formulated into 6 kinds of test feeds with isonitrogen and isolipids, and the initial body weight of (34.14±0.15) g juvenile A. davidianus was reared. The results showed that: the increase in the weight gain rate (WGR) of A. davidianus's vitamin C addition level showed a trend of first increasing and then becoming stable, reaching the maximum when the vitamin C level was 450 mg/kg, which was 102.04%. With the increase of vitamin C level, the activities of pepsin and H⁺-K⁺-ATPase of A. davidianus both increased first and then decreased; and reached the strongest when the vitamin C level was 300 mg/kg; intestinal chymotrypsin, lipase and activity of Na⁺-K⁺-ATPase increased with the increase of vitamin C level and showed a trend of first rising and then tending to be stable, and both reached the strongest when the vitamin C level was 450 mg/kg (P<0.05); it was found through observation of tissue sections when the vitamin C level is 300 mg/kg that it is more conducive to the development of the gastric and intestinal muscle layer and villi of A. davidianus (P<0.05); with the increase of vitamin C level, the activities of CAT, T-SOD, ACP and AKP in the liver of A. davidianus all showed the trend of rising first and then falling. The activity of MDA, AST and ALT showed the opposite trend of change. Moreover, with the addition of vitamin C, the infiltration of inflammatory cells in the liver of A. davidianus was significantly reduced, and the number of macrophages was significantly increased. In summary, proper amount of vitamin C can effectively improve the structure of the digestive tract of A. davidianus, enhance its digestive enzyme activity, improve its growth performance, enhance liver antioxidant capacity, and effectively protect liver health.

Abstract:A 3-week feeding trial was conducted to determine the optimal dietary vitamin C requirement of largemouth bass (Micropterus salmoides) larva [(1.2±0.3) mg]. Five practical diets were formulated to contain 0 (V0), 200 (V200), 400 (V400), 800 (V800) and 1 600 (V1600) mg/kg vitamin C. Each experimental diet was fed to triplicate groups of fish to apparent satiation seven times a day. At the end of the experiment, the results showed that the final body weight, weight gain rate and specific growth rate increased with the increase of dietary vitamin C level, and then tended to be stable, with the highest values in VC400 group. Weight gain rate (WGR) and specific growth rate (SGR) markedly increased with increasing dietary vitamin C supply and then leveled off while body ASA concentration continued to increase with increasing dietary vitamin C supply. Vitamin C supplementation not only increased antioxidant capacities [activity of catalase (CAT)], reduced glutathione content (GSH), superoxide dismutase (SOD) and immunocompetence [complement C3, complement C4 and lysozyme(LZM) concentration)] of the larva, but also decreased lipid peroxidation (malondialdehyde (MAD) concentration) in the body. Broken-line analysis showed that the optimal dietary vitamin C requirement of M. salmoides was 421.2 mg/kg based on WGR. In practical production of largemouth bass larvae, 420 mg/kg of dietary vitamin C should be recommended to maintain normal physiological function.

Abstract:The demand for aquatic products has grown recently, and consumers are more concerned with the safety and quality of fish meat for consumption. This paper will explore the technical feasibility of short-term fasting to improve the food quality of pond cultured fish, commercial Ctenopharyngodon idella cultured in three adjacent ponds were taken as the objects and transferred to three cages in another pond for 21 days of short-term fasting. C. idella from three ponds were collected every seven days, and the fish body was divided into four body segments A, B, C and D muscle samples were collected for quantitative analysis of muscle moisture, crude protein, crude lipid and glycogen content. The results showed that the nutrient content of muscle of different body segments changed after fasting for 7 days, and the crude protein content and crude lipid content changed significantly after fasting for 14 days, and the crude protein content of tail (C and D segments) increased significantly; The crude lipid content of a segment of C. idella from No.10 pond was 22.60% and 17.07% lower than that of 0 d on 14 and 21 days, respectively. The crude lipid content of B and D segments was 7.50%, 19.41%, 12.61% and 28.83%, 36.68%, 13.49% lower than that of 0 d on 7, 14 and 21 days, respectively. The crude lipid content of A, C and D segments of C. idella from No.17 pond was significantly increased after 7 days. The crude lipid content of B segment was 26.76%, 58.41% and 62.90% lower than that of 0 d on 7, 14 and 21 days, respectively. The crude lipid content of D segment was 1.52% and 22.58% lower than that of 0 d on 7 and 14 days, respectively. The glycogen content (C, D segments) of C. idella muscle from three ponds showed a significant increase trend. The back muscle samples of C. idella were collected, and the water power, muscle texture characteristics and tissue sections of the muscle system were measured. It was found that there was no significant difference in the drip loss rate of the back muscle of C. idella from pond 10 on day 14, the drip loss rate of the back muscle of C. idella from pond 17 on day 14 was significantly higher than that of day 0, and the drip loss rate of the back muscle of C. idella from pond 18 on day 14 had a downward trend. With the extension of fasting time, the hardness of the B segment muscle of C. idella from three ponds decreased, and the muscle elasticity increased. Chewiness increased gradually before 14 days, while cohesion increased gradually. During fasting, the density of back muscle fibers (muscle cells) increased, the gap between muscle fibers decreased, and the muscle hardness gradually decreased with fasting time, while the elasticity and chewiness showed a gradual increase trend. The results showed that short-term fasting could change the eating quality of C. idella muscle, and the best experimental result was fasting for 14 days. The results of this study provide a scientific basis for improving the food quality of pond cultured fish.

Abstract:Riboflavin as an indispensable water-soluble B vitamin, is particularly crucial for the growth and metabolism of animals. It often participates in biochemical reactions as flavin adenine dinucleotide (FAD) and flavin mononucleotides (FMN), and plays a key role in the normal growth and the development of animal body. To date, the research data on the appropriate vitamin requirements of oriental river prawn (Macrobrachium nipponense) are relatively lacking compared to other nutrients, which has slowed the process of research and development of formula feed, as well as hindered the efficient and economic development of aquaculture. Therefore, this experiment was conducted to investigate the effects of different dietary riboflavin levels on the growth performance and metabolic function of M. nipponense, in order to help the construction of the nutritional requirements database of this species, and facilitate the development of high quality formula feed. A total of 1200 oriental river prawns with an average weight of 0.68 g were picked out, and randomly separated into 6 groups, with 4 replicates in each group, and 50 prawns in each tank, respectively. Six semi-purified diets were prepared, containing 3.91, 20.53, 49.18, 87.80, 169.61 and 326.66 mg/kg of riboflavin. Subsequently, a 10-week feeding trial was conducted in an indoor recirculation water system. The results showed that: ① the 169.61 mg/kg group had significantly higher final weight, weight gain rate, specific growth rate, protein retention rate, plasma pyruvate level, and hepatopancreatic riboflavin content compared with other groups, while the feed intake, feed conversion ratio, and plasma urea nitrogen levels were significantly lower than the other groups. Using the weight gain rate and hepatopancreatic riboflavin content as evaluation indicators to establish the regression models, it was indicated that the optimal riboflavin requirement of M. nipponense was 165.25-180.31 mg/kg; ② the mRNA levels of glucose transporter 2, hexokinase, pyruvate kinase, hormone sensitive lipase, glutamate dehydrogenase, and glutamine synthase all increased significantly with the increase of dietary riboflavin levels, and maximized in the 169.61 mg/kg group, then decreased; the mRNA levels of pyruvate carboxylase, fatty acid synthase, and acetyl CoA carboxylase all showed an opposite result, and minimized in the 169.61 mg/kg group. In summary, adding 165.25-180.31 mg/kg of riboflavin significantly promoted the growth performance and feed utilization of M. nipponense, and enhanced the glycolysis, fatty acids β-oxidation, and protein synthesis pathways. This study preliminarily clarified the molecular mechanism of riboflavin to improve the growth performance and metabolic function of M. nipponense, which can provide technical guidance for the construction of nutrition demand database of M. nipponense and the research and development of efficient formula feed.

Abstract:Lipoprotein lipase (LPL) is a key enzyme in fat hydrolysis. In order to study the gene characteristics, temporal and spatial expression distribution and enzyme activity of Cyprinus carpio LPLs (CcLPLs), the homologous genes of CcLPLs were obtained by homology searches through C. carpio genome and the sequence characteristics were analyzed. The expression analysis of CcLPLs in different tissues was carried out by qPCR. CcLPLs recombinant protein were obtained by prokaryotic expression system, and the enzyme activity of recombinant proteins was determined by p-nitrophenol method. The results are as follows. Five CcLPLs homologous genes (CcLPLA1a, CcLPLA1b, CcLPLA2a, CcLPLA2b* and CcLPLBa) were excavated from the carp genome, of which CcLPLA2b* is a pseudogene. The collinearity analysis showed that gene loss occurred during the doubling of the fish-specific genome, while the doubling of the carp-specific genome resulted in the presence of five CcLPLs in carp. By Homology analysis, CcLPLBa shared 64% indentity with CcLPLA1s and 50.8% with CcLPLA2a. qPCR showed that the expression of CcLPLs decreased by degrees in liver, heart, fat, muscle, brain, intestine and spleen. In each tissue, the expression of CcLPLA1s was significantly higher than that of CcLPLA2a, and the expression of CcLPLA2a was significantly higher than that of CcLPLBa. The expression levels of CcLPLA1s and CcLPLA2a in liver, muscle and adipose tissues under normal feeding, starvation and refeeding conditions were determined by qPCR. The results showed that the expression levels of CcLPLA1s and CcLPLA2a in liver under starvation were significantly higher than those in the normal feeding group, while the expression levels in muscle and adipose tissue were opposite to those in liver. After refeeding, the expression levels of CcLPLA1s and CcLPLA2a were restored as normal feeding group in the three tissues. Using E. coli expression system, Skp-CcLPLs and SlyD-CcLPLs recombinant proteins were obtained. The enzymatic activity of each recombinant protein was determined by the p-nitrophenol method, and the results were (24.12 ±0.96), (22.66 ±0.46), (21.48 ±0.47), (21.13 ±0.46), (18.07 ±0.39) and (16.49 ±0.31) U/g for SlyD-CcLPLA1a, Skp-CcLPLA1a, Skp-CcLPLBa, Skp-CcLPLA2a, SlyD-CcLPLBa and SlyD-CcLPLA2a, respectively. Regardless of Skp or SlyD tags in the recombinant proteins, the enzymatic activities of CcLPLs from high to low were CcLPLA1a, CcLPLBa and CcLPLA2a. Determination of effect of pH and NaCl concentration on enzyme activity showed the optimal reaction condition of pH was 8.0 and the NaCl concentration that exerted the maximum activity was 0.6 mol/L. In conclusion, we explored the evolutionary expression of CcLPLs homologous genes, analyzed the temporal and spatial expression of CcLPLA1s, CcLPLA2a and CcLPLBa. The effects of starvation and refeeding on the expression of CcLPLA1s and CcLPLA2a were studied, and the results revealed the lipid metabolism and response countermeasures under starvation stress, and provided a targrt for controlling the fat content in C. carpio. The prokaryotic expressions of the recombinant proteins were successfully carried out and the enzymatic activites were determined, which provided a reference for the study of fish lipoprotein lipase.

Abstract:Enrofloxacin (ENR) is an antibiotic with rapid absorption and distribution, high blood concentration, long-term efficacy and high bioavailability, which has been widely used in preventing and treating of fish diseases. However, in recent years, the impact of ENR residues is a growing public concern on human and ecological safety. On the basis of studies on ENR elimination in fish, the structure and properties of ENR, the relationship between ENR and fish species, developmental stages, tissue differences, physiological and pathological conditions, dosages and modes of administration and environmental factors such as temperature, salinity, light, were reviewed, and the cause of formation of ENR residues in fish was analyzed retrospectively in this paper. For the first time, the hypothesis was firstly found and proposed that benthic fishes were more likely to form ENR residues than other water layer fishes, which probably was related to the ENR absorption by the organic matter in the sediment, and the photolysis of ENR could not be achieved in the dark sediment environment. It is suggested that the withdrawal period of ENR in bottom fishes should be redefined, and the mechanism of ENR residue in benthic fishes should be emphatically studied. It is proposed for the first time that the high dose ENR administration based on the selective mutation window theory is the main source of ENR residues in fish and environment.Therefore, in order to reduce ENR residue in cultured fish and environment, a reduction ENR dosing regimen was proposed on the basis of minimum inhibitory concentration of ENR, combining traditional Chinese herbal medicines with antibacterial and detoxification functions, to promote the elimination of ENR residues in fish, shorten the withdrawal period of ENR in fish, and reduce the risk of ENR resisting bacteria. At the same time, in order to reduce the environmental source of fish ENR, environmental ENR elimination techniques should be studied at the same time. This paper can provide new ideas for the scientific regimen of ENR and the risk control of ENR residues in cultured fish and environment.