The extracts of Angelica sinensis restore the digestive and absorptive capacity through improving antioxidant status in digestive organs of fish treated with trichlorfon

Firstly, a linoleic acid emulsion and fish hepatopancreas homogenate were incubated with ethoxyquin and the extracts of Angelica sinensis. The results demonstrated that ethoxyquin showed the strongest protective effects against lipid oxidation of all of the examined compounds (p < 0.05). However, ethyl acetate extract of Angelica sinensis at high concentrations showed a stronger effect on lipid oxidation than that of ethoxyquin (p < 0.05). Next, seven experimental diets that contained 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 g/kg of ethyl acetate extract of Angelica sinensis were fed to seven groups of carp (Cyprinus carpio var. Jian) respectively. After 60 days, carp were exposed to 2.4 mg trichlorfon/L in water for 4 days. The results displayed that trichlorfon exposure increased the contents of malonaldehyde and protein carbonyl in digestive organs and the activities of glutamate‐oxaloacetate and glutamate‐pyruvate transaminase in plasma, and decreased feed intake, the level of reduced glutathione, and the activities of trypsin, chymotrypsin, lipase, alpha‐amylase, Na⁺,K⁺‐ATPase, alkaline phosphatase, antisuperoxide anion, antihydroxyl radical, superoxide dismutase, glutathione reductase, and glutathione S‐transferase in digestive organs of carp (p < 0.05). Moreover, the dietary ethyl acetate extract of Angelica sinensis prevented the decrease in the above parameters in carp treated with trichlorfon (p < 0.05). These results revealed that the dietary ethyl acetate extract of Angelica sinensis could quench the trichlorfon‐induced structural and functional damage by improving the antioxidative capacity of the digestive organs of fish. Therefore, the extract of Angelica sinensis could be used as an inhibitor of trichlorfon stress in fish.     

Effects of dietary phenylalanine on growth,digestive and brush border enzyme activities and antioxidant capacity in the hepatopancreas and intestine of young grass carp (Ctenopharyngodon idella)

This study investigated the effects of phenylalanine on growth, digestive and absorptive ability and antioxidant status of young grass carp (Ctenopharyngodon idella). Young grass carp were fed diets containing 3.4 (basal diet), 6.1, 9.1, 11.5, 14.0 and 16.8 g phenylalanine kg^?1 diet with a fixed of 10.7 g tyrosine kg^?1 diet for 8 weeks. Percent weight gain (PWG), feed efficiency and feed intake of fish were the lowest in fish fed the basal diet (P < 0.05). Trypsin, lipase and amylase activities in the hepatopancreas, and antioxidants including glutathione contents and glutathione reducase activities in the hepatopancreas and intestine were all the highest in fish fed 11.5 g phenylalanine kg^?1 diet (P < 0.05). Trypsin, chymotrypsin and amylase activities in whole intestine, and creatine kinase, Na⁺, K⁺‐ATPase and alkaline phosphatase activities in the proximal intestine, and superoxide dismutase activities in the hepatopancreas and intestine were all the highest when phenylalanine at level of 9.1 g kg^?1 diet (P < 0.05). In conclusion, phenylalanine improved growth, digestive and absorptive ability, and antioxidant capacity of young grass carp. The phenylalanine requirement of young grass carp (256–629 g) based on PWG was 10.4 g kg^?1 diet or 3.44 g 100 g^?1 protein.     

Effects of dietary lipid source on fatty acid composition,expression of genes involved in lipid metabolism and antioxidant status of grass carp (Ctenopharyngodon idellus)

This study determined the effect of different lipid sources on growth, feed use, lipid metabolism and antioxidant status of grass carp (Ctenopharyngodon idellus). Juvenile fish (56.9 ± 4.7 g) were divided into four triplicate groups and fed diets containing 30 g/Kg of fish oil (FO), olive oil (OO), peanut oil (PO) and linseed oil (LO), respectively, for 60 days. Weight gain and feed conversion ratio were not significantly different between the dietary groups, but we observed changes in the fatty acid composition of muscle and intraperitoneal fat reflecting the fatty acid profile of the dietary lipid source. In the hepatopancreas, the highest mRNA level of fatty acid translocase CD36 (FAT/CD36) and carnitine palmitoyl transferase (CPT‐1A) was both observed in the FO group. In muscle, the expression of FAT/CD36 and CPT‐1A in the LO group was significantly higher than that in other groups, except for CPT‐1A in the PO group. In addition, the lowest and highest content of malondialdehyde in serum was observed in OO and FO groups, respectively. In summary, dietary lipid source altered the fatty acid composition, potential uptake (FAT/CD36) and oxidation (CPT‐1A) of fatty acids, and antioxidant status of grass carp, which should be considered when selecting a lipid source.     

Comparative study on the effect of high dietary carbohydrate on the growth performance,body composition,serum physiological responses and hepatic antioxidant abilities in Wuchang bream (Megalobrama amblycephala) and black carp (Mylopharyngodon piceus Richardson, 1846)

A 90‐day trial investigated the effect of dietary carbohydrate level on growth performance, body composition, serum physiological responses and hepatic antioxidant abilities of a herbivorous fish, Wuchang bream (Megalobrama amblycephala) and a carnivorous fish, black carp (Mylopharyngodon piceus Richardson, 1846). For each species, two isonitrogenous and isolipidic semi‐purified diets (28.6% crude protein and 5.3% crude lipid for Wuchang bream) were formulated to contain 30.4% and 52.9% carbohydrate (WB‐NCHO and WB‐HCHO); Two isonitrogenous and isolipidic semi‐purified diets (32.6% crude protein and 5.3% crude lipid for black carp) were formulated to contain 20.5% and 40.5% carbohydrate (BC‐NCHO and BC‐HCHO). It was shown that, compared to Group WB‐NCHO, Wuchang bream in Group WB‐HCHO had lower weight gain rate, specific growth rate, serum total protein, hepatic superoxide dismutase activity and total antioxidative capacity, while higher feed conversion ratio, serum triglyceride and cortisol levels (P < 0.05). Compared to Group BC‐NCHO, black carp in Group BC‐HCHO had lower final weight, weight gain rate, specific growth rate, protein efficiency ratio, serum alkaline alkaline phosphatase activity, serum total protein, hepatic superoxide dismutase activity and total antioxidative capacity, while higher feed conversion ratio, whole body crude lipid, serum triglyceride, cholesterol, glutamic‐oxaloacetic transaminase activity and cortisol levels (P < 0.05). The results of this study suggested that Wuchang bream had better capacity of utilizing dietary carbohydrate than that of black carp, while high levels of dietary carbohydrate might not only be detrimental to growth performance and feed utilization but also the immune response and health for both species.     

Influence of dietary zinc on lipid peroxidation,protein oxidation and antioxidant defence of juvenile Jian carp (Cyprinus carpio var. Jian)

This study was conducted to study the effects of dietary zinc on lipid peroxidation, protein oxidation and antioxidant defence of juvenile Jian carp (Cyprinus carpio var. Jian) by feeding fish with increasing levels of zinc (15.3, 26.9, 40.8, 58.2, 68.9 and 92.5 mg Zn kg^?1) for 6 weeks. Results indicated that malondialdehyde (MDA) content and protein carbonyls (PC) in serum were the highest in fish fed diet containing 15.3 mg zinc kg^?1 diet (P < 0.05). Serum antisuperoxide anion (ASA), superoxide dismutase (SOD), glutathione peroxidase (GSH‐Px), glutathione reductase (GR) activities and glutathione (GSH) content were improved with increasing dietary zinc levels up to 40.8 mg zinc kg^?1 diet (P < 0.05) and levelled off (P > 0.05). Serum antihydroxy radical (AHR), catalase (CAT) and glutathione‐S‐transferase (GST) activities followed the similar pattern to that observed in ASA. The MDA and PC levels, ASA, AHR, SOD, CAT, GPx, GR, GST activities and GSH content in intestine, hepatosomatic and muscle tissue followed the similar pattern to that observed in serum. The present results indicated that zinc decreased lipid peroxidation and protein oxidation and improved antioxidant defence in fish.     

Hepatoprotective and antioxidant effects of dietary Angelica sinensis extract against carbon tetrachloride‐induced hepatic injury in Jian Carp (Cyprinus carpio var. Jian)

The present study aimed to evaluate the hepatoprotective effects of Angelica sinensis extract (ASE) against carbon tetrachloride (CCl₄)‐induced hepatotoxicity in Jian carp (Cyprinus carpio var.Jian). Fish were fed diets containing four doses of ASE (0%, 0.1%, 0.5% and 1.0%) for 60 days, and then given an intraperitoneal injection of 30% CCl₄ in olive oil at a volume of 0.05 mL/10 g body weight. At 72 h post injection, blood and liver samples were collected for biochemical analysis, comet assay, histopathological examination and CYP3A mRNA expression. Results showed that the increases of glutamate pyruvate transaminase (GPT) and glutamate oxalate transaminase (GOT) induced by CCl₄ were significantly inhibited by pre‐treating the fish with 0.1%, 0.5% and 1.0% ASE in the diets. The elevation of lactate dehydrogenase (LDH) and the reductions of the total protein (TP) and albumin (Alb) in the serum induced by CCl₄ were also inhibited by pre‐treatments with 0.5 and 1.0% ASE. In the liver tissue, pre‐treatment with 1.0% ASE significantly inhibited the malondialdehyde (MDA) formation and the reductions of the total antioxidant capacity (T‐AOC), superoxide dismutase (SOD), glutathione (GSH) and CYP3A mRNA expression induced by CCl₄. Comet assay showed that tail moment, olive tail moment, tail length and tail DNA% were positively changed in fish pretreated with 0.5 and 1.0% ASE. CCl₄‐induced histological changes were obviously reduced by 0.5% and 1.0% ASE. Overall results prove the hepatoprotective effect of ASE in a dose‐dependent manner and support the use of ASE (1.0%) as a hepatoprotective and antioxidant agent in fish.     

Effects of dietary vitamin C and vitamin E on the growth,antioxidant defence and digestive enzyme activities of juvenile discus fish (Symphysodon haraldi)

A 56‐day experiment was carried out to investigate the effects of dietary vitamin C and vitamin E on the growth, antioxidant status and digestive enzyme activities of discus fish (Symphysodon haraldi; initial body weight: 7.96 ± 0.61 g and body length: 5.45 ± 0.65 cm). Animals were fed with 13 different diets including one control diet and 12 treatment diets containing four levels of vitamin C (magnesium‐L‐ascorbyl‐2‐phosphate; 40, 80, 120 and 160 mg/kg) crossed with three levels of vitamin E (DL‐α‐tocopheryl acetate; 40, 80 and 120 mg/kg). The results showed that the fish fed diets containing additional vitamin C (40 mg/kg) and vitamin E (80 mg/kg) showed higher specific growth rate, length growth rate, total antioxidant capacity and protease activity but had lower feed conversion ratio and total superoxide dismutase activity than those fed the control diet. Collectively, these findings suggest that the inclusion of additional 40 mg/kg of vitamin C and 80 mg/kg of vitamin E in the basal diet could have beneficial effect on the growth, antioxidant defence and digestion of S. haraldi.     

Effects of dissolved oxygen on the growth performance,haematological parameters,antioxidant responses and apoptosis of juvenile GIFT (Oreochromis niloticus)

This study investigated the effects of different dissolved oxygen (DO) levels on the growth performance, antioxidant response and apoptosis of juvenile GIFT (genetically improved farmed tilapia, Oreochromis niloticus). GIFT were fed with five DO levels (1, 2, 3, 4 and 5 mg/L) for 60 days, and the results showed that the final body weight, weight gain rate, specific growth rate and crude protein and crude lipid contents of the fish muscle increased at 5 mg/L DO. The activities of the antioxidant and digestive enzymes were significantly up‐regulated with increasing DO levels. However, the haemoglobin content, number of red blood cells, malondialdehyde content, transaminase activities, glucose content and lactic acid levels decreased at higher DO levels. Furthermore, the cardiomyocyte apoptotic index was significantly decreased with increasing DO levels. Our results show that 5 mg/L DO improved growth performance, promoted antioxidant enzyme activities and reduced liver damage in GIFT.     

Growth performance,haematology, antioxidant status,immune response and histology of common carp (Cyprinus carpio L.) fed biofloc grown on different carbon sources

A 10 weeks trial was performed to investigate how different carbon sources (sugar beet molasses: SBM+BFT, sugar: S+BFT, corn starch: CS+BFT) along with control affect welfare status of common carp (Cyprinus carpio L.) fingerlings in biofloc‐based tanks. Three hundred healthy fingerlings (22.5 ± 0.2 g) were randomly distributed in 12 tanks (70 L) at a density of 8.02 kg/m³ (25 fish/tank). The fish in BFT treatments fed only 75% feeding rate of control. At the end of the experiment no differences were seen between the groups in case of growth performance, but the fish reared in CS+BFT had a significant lower food conversion ratio compared with the others (p < .05). Different carbon sources did not affect on haematological parameters (p > .05). Total serum protein and antibody concentration differed in treatments, and the highest values were found in S+BFT and CS+BFT treatments (p < .05). No significant differences were observed in case of lysozyme, superoxide dismutase and complement activity in treatments (p > .05), whereas the fish in BFT treatments showed a significant higher total antioxidant capacity and lower glutathione peroxidase than the control (p < .05). Different carbon sources resulted in no change in goblet and kupffer cells in intestine and liver respectively. The highest relative percentage survival was obtained in the CS+BFT and S+BFT (50%) in comparison with SBM+BFT (20%) treatment. The results obtained in this experiment, suggest that corn starch improves immune response, diseases resistance and histology of digestive and respiratory systems in carp fingerlings when used as a carbon source in zero water exchange system.     

Effect of dietary common carp by‐product protein hydrolysates on antioxidant status in different organs of zebrafish (Danio rerio)

A feeding trial was conducted to evaluate the effect of dietary protein hydrolysates from common carp (Cyprinus carpio) by‐products on the antioxidant status of zebrafish (Danio rerio). Common carp by‐product was hydrolysed using Alcalase to a degree of hydrolysis of 15%. The zebrafish were fed for 44 days with four different diets with increasing levels of carp by‐product hydrolysates (CBH0: 0 g/kg; CBH25: 25 g/kg; CBH50: 50 g/kg; CBH100: 100 g/kg). The gills, muscle and brain were dissected at the end of the feeding trial in order to evaluate the total antioxidant capacity against peroxyl radicals (ACAP) and lipid peroxidation (TBARS). Although total antioxidant capacity did not show differences in muscle (p > 0.05), lipid peroxidation was reduced in the muscle of fish fed the CBH50 diet. Brain lipid peroxidation showed a significant reduction (p < 0.05) in all groups when compared with the control diet CBH0. Antioxidant properties of protein hydrolysates indicate their potential as nutraceuticals since (a) a reduction in muscle lipid peroxidation was verified, implying that their use could enhance the quality and shelf life of fish fillets; and (b) a decrease in brain lipid peroxidation was registered, highlighting the potential use of fish protein hydrolysates for the prevention of neurodegenerative diseases.     

Modulation of growth performances,survival, digestive enzyme activities and intestinal microbiota in common carp (Cyprinus carpio) larvae using short chain fructooligosaccharide

This study investigates the effects of inclusion of low levels of dietary short chain fructooligosacchairde (sc‐FOS) on physiological response and intestinal microbiota of carp (Cyprinus carpio) larvae. After acclimation, fish (550 ± 20 mg) were allocated into nine tanks (40 fish per tank) and triplicate groups were fed a control diet (0%) or diets containing 0.5% and 1% sc‐FOS for 7 weeks. At the end of the experiment, the growth performance parameters (final weight, weight gain, specific growth rate (SGR), food conversion ratio (FCR) and condition factor (CF), survival rate as well as digestive enzyme activities (amylase, lipase and protease), total viable counts of heterotrophic aerobic bacteria (TVC) and lactic acid bacteria (LAB) level in intestinal microbiota were measured. Our results revealed no significant (P > 0.05) effects of sc‐FOS on growth performance and TVC when compared with the control group. However, administration of low levels of dietary sc‐FOS significantly increased digestive enzyme activities (lipase and amylase) and LAB levels (P < 0.05). Also, survival rate was significantly elevated in sc‐FOS fed carp. These results revealed that administration of low levels of sc‐FOS can be considered as a beneficial dietary supplement for larval stage of common carp.     

Effects of dietary vitamin K levels on growth performance,enzyme activities and antioxidant status in the hepatopancreas and intestine of juvenile Jian carp (Cyprinus carpio var. Jian)

A total of 1400 juvenile Jian carp (Cyprinus carpio var. Jian) (8.93 ± 0.03 g) were fed diets containing graded levels of vitamin K at 0.027 (basal diet), 1.52, 3.02, 4.51, 6.02 and 7.52 mg kg^?1 diet for 60 days to investigate the effects of vitamin K on growth, enzyme activities and antioxidant capacity in the hepatopancreas and intestine. Percentage weight gain (PWG), feed intake and feed efficiency of fish were improved by vitamin K. Activities of trypsin, chymotrypsin, amylase and lipase in the intestine and hepatopancreas and Na⁺, K⁺‐ATPase, creatine kinase, alkaline phosphatase and gamma‐glutamyl transpeptidase in the intestine were increased by vitamin K. Malondialdehyde and protein carbonyl contents in the hepatopancreas and intestine were decreased with vitamin K supplements. Certain level of vitamin K increased antihydroxyl radical, antisuperoxide anion, superoxide dismutase, catalase, glutathione‐S‐transferase, glutathione peroxidase and glutathione reductase activities and glutathione contents in the hepatopancreas and intestine. Intestinal Lactobacillus, E. coli and Aeromonas were changed with vitamin K supplements. Together, these results indicate that vitamin K improved fish growth, digestive and absorptive ability, and anti‐oxidant capacity. The dietary vitamin K requirement of juvenile Jian carp (8.93–73.7 g) based on PWG was 3.13 mg kg^?1 diet.     

Effects of dietary vitamin C on growth,gonad development and antioxidant ability of on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

An 88‐day experiment was conducted in a flowing system to evaluate the effects of dietary vitamin C on growth, body composition, antioxidant and gonad development of on‐growing gibel carp. Triplicate tanks of gibel carp (77.2 ± 0.1 g) were randomly fed with one of seven experimental diets containing l ‐ascorbic acid of 0, 101.1, 188.5, 313.1, 444.1, 582.1 and 747.0 mg/kg, respectively. The results showed that specific growth rate (SGR) and feed efficiency (FE) of fish were not affected by dietary l ‐ascorbic acid. Dietary l ‐ascorbic acid of 444.1 mg/kg diet led to low levels (p < .05) of gonadosomatic index (GSI) and hypothalamic gonadotropin‐releasing hormone (GnRH) in on‐growing fish, as well as the early ovarian stages (Developing stages) compared with fish (Maturing stages) from the other groups. Dietary l ‐ascorbic acid supplementation increased (p < .05) the dorsal muscle collagen content, but did not affect the protein or lipid content of dorsal muscle in gibel carp. Plasma total antioxidant capacity (T‐AOC) and superoxide dismutase (SOD) activity increased (p < .05) and then remained unchanged with the increase in dietary l ‐ascorbic acid levels. Dietary l ‐ascorbic acid of 101.1 mg/kg diet improved (p < .05) plasma lysozyme activity of the fish. Broken‐line regression indicated that dietary l ‐ascorbic acid requirement of 77 g gibel carp was 223.3 or 225.0 mg/kg diet based on plasma T‐AOC or SOD activity, which was a little higher than that based on plasma l ‐ascorbic acid concentration (193.2 mg/kg).     

Antiviral activities of Clinacanthus nutans (Burm.f.) Lindau extract against Cyprinid herpesvirus 3 in koi (Cyprinus carpio koi)

Cyprinid herpesvirus 3 (CyHV‐3) or koi herpesvirus (KHV) is a virulent viral infection in common carp and koi. The disease has caused global epizootic and economic loss in fish aquaculture and in the wild. Clinacanthus nutans (Burm. f.) Lindau is a well‐known medicinal plant used in Thai traditional medicine. Virucidal effects of the plant extract against human herpes simplex virus have been reported. In this study, C. nutans crude extract was tested for antiviral activities against CyHV‐3 in koi carp. Results showed effective antiviral activity against CyHV‐3 pre‐ and post‐infection. The 50% lethal concentration (LC₅₀) of extract was higher than 5 mg/ml. The 50% effective dose (ED₅₀) was 0.99 mg/ml, 0.78 mg/ml, 0.75 mg/ml and 0.71 mg/ml at 1, 2, 3 and 4 hr pre‐infection, respectively. The ED₅₀ from post‐infection tests was 2.05 mg/ml and 2.34 mg/ml at 0 and 24 hr, respectively. These results demonstrated that crude extract expressed antiviral activity against CyHV‐3 and can be applied as a therapeutic agent in common carp and koi aquaculture.     

Effects of dietary ethoxyquin on growth,feed utilization and residue in the muscle of juvenile Japanese seabass,Lateolabrax japonicus

Ethoxyquin (EQ) is the most common synthetic antioxidant used for preventing rancidity in fish foodstuffs. However, literature related to the effects of dietary EQ on performance of fish was limited. The present study was conducted to investigate the effects of EQ on performance and EQ residue in muscle of juvenile Japanese seabass Lateolabrax japonicus and to estimate the optimal EQ concentration in the diet. Graded levels [0 (control), 50, 150, 450 and 1350 mg EQ kg^?1 diet] of EQ were added to the basal diet, resulting in five dietary treatments in the experiment. Each diet was fed to triplicate groups of seabass (initial body weight 8.01 ± 0.76 g) for 12 weeks in floating sea cages (1.5 × 1.5 × 2.0 m, 30 fish per cage). Survival ranged from 78.9 to 86.7%, and was irrespective of dietary EQ levels. The specific growth rate (SGR) of fish fed diets supplemented with ≤50 mg kg^?1 EQ had significantly (P < 0.05) higher SGR than fish fed diets supplemented with ≥150 mg kg^?1 EQ, the highest SGR was observed in fish fed diet with 50 mg kg^?1 EQ supplementation. Feed intake (FI) and feed efficiency (FE) were not significantly (P > 0.05) different among dietary treatments. Fish fed diets with 50 and 1350 mg kg^?1 EQ had a significant (P < 0.05) lower body lipid content than fish in the control group. Muscle EQ level significantly increased when dietary EQ increased. Optimal EQ concentration estimated by polynomial regression based on maximum growth of juvenile Japanese seabass was 13.78 mg kg^?1 diet.     

Effects of pyridoxine on antioxidative parameters in juvenile Jian carp (Cyprinus carpio var. Jian)

To investigate the effects of dietary pyridoxine (PN) on antioxidant status of fish in serum, intestine and trunk kidney, 1050 juvenile Jian carp (11.7 ± 0.1 g) were used for the experiment. The carp were divided into seven groups and fed diets containing graded levels of PN (0.20, 1.71, 3.23, 4.96, 6.32, 8.58 and 12.39 mg kg^?1 of diet) for 80 days. Results of the study showed that content of malondialdehyde in serum, intestine and kidney tissues was the highest when fed the diet containing 1.71 mg PN kg^?1 diet (P < 0.05). Meanwhile, the protein carbonyl content of intestine and kidney tissue showed a downward trend to a point (P < 0.05). Conversely, activities of superoxide dismutase, catalase, glutathione peroxidase (GSH‐Px), glutathione S‐transferase, glutathione reductase and glutathione (GSH) content in serum, intestine and kidney tissue were generally higher in PN‐supplemented diets than unsupplemented diet (P < 0.05). The present results indicated that the PN decreased lipid peroxidation and protein oxidation in fish, and partly because of its improved antioxidant enzymes activities and levels of GSH.     

Effect of replacing dietary fish meal with black soldier fly larvae meal on growth and fatty acid composition of Jian carp (Cyprinus carpio var. Jian)

To explore the effect of replacing dietary fish meal (FM) with black soldier fly (Hermetia illucens) larvae meal (BSFLM) on growth and body composition of Jian carp (Cyprinus carpio var. Jian), the FM in basal diet of Jian carp was replaced by 0, 35, 70, 105 and 140 g/kg BSFLM respectively to form five isonitrogenous and isolipidic diets. A total of 300 Jian carp (10.1 ± 1.6 g) were randomly divided into five groups (triplicate per group) and fed five diets, respectively. After 56 days of feeding, growth and body composition of fish were determined. Results showed that serum maleic dialdehyde, total antioxidant capacity, 18:1n‐9, 18:2n‐6, 20:5n‐3 and 22:6n‐3 in fish significantly decreased and 12:0, 14:0 and 16:0 significantly increased with increasing replacement of BSFLM. The growth, biological parameters, proximate composition, amino acid composition and serum biochemical parameters of Jian carp were not affected by the replacement of BSFLM. In conclusion, up to 140 g/kg BSFLM (100% replacement of FM) can be included in diets of Jian carp without unfavourable effects on growth while decreasing n‐3 highly unsaturated fatty acid (HUFA) composition in body of fish, suggesting that BSFLM could be used after nutrient enrichment with n‐3 HUFA to bring active effects on fish quality.     

Effects of dietary biotin supplement on growth,body composition,intestinal enzyme activities and microbiota of juvenile Jian carp (Cyprinus carpio var. Jian)

A total of 1400 juvenile Jian carp (Cyprinus carpio var. Jian) (7.72 ± 0.02 g) were fed seven purified diets containing 0.010 (basal diet), 0.028, 0.054, 0.151, 0.330, 1.540 and 2.680 mg biotin kg^?1 for 63 days to investigate the effects of biotin on growth, body composition, intestinal enzyme activities and microbiota. Specific growth rate (SGR), feed intake, feed efficiency and protein retention value were the highest when dietary biotin level was 0.151 mg kg^?1 diet. Crude protein, lipid and ash content of fish carcass improved with increasing dietary biotin levels up to 0.054, 0.151 and 0.028 mg kg^?1 diet, respectively (P < 0.05). Intestinal folds height, trypsin, chymotrypsin, lipase, amylase, alkaline phosphatase, Na⁺, K⁺‐ATPase, γ‐glutamyl transpeptidase and creatinekinase activities increased with dietary biotin levels up to 0.151–0.330 mg kg^?1 diet (P < 0.05). Intestinal Aeromonas and Escherichia coli significantly decreased with increasing dietary biotin up to 0.151 mg kg^?1 diet, while Lactobacillus and Bacillus significantly increased with dietary biotin levels up to 0.054 and 0.151 mg kg^?1 diet, respectively. In conclusion, biotin could improve digestive and absorptive ability of fish, and the dietary biotin requirement for SGR of juvenile Jian carp (7.72–32.67 g) was 0.15 mg kg^?1 diet.     

Effect of dietary iron levels on growth,body composition and intestinal enzyme activities of juvenile Jian carp (Cyprinus carpio var. Jian)

A 60‐day feeding trial was carried out to investigate the effect of iron on growth, body composition and digestive enzyme activities. Diets with seven levels of iron (53.9, 90.0, 115.6, 146.1, 176.0, 215.8 and 266.0 mg iron kg^?1 diet) were fed to Jian carp (initial weight 11.4 ± 0.0 g). Per cent weight gain (PWG), feed efficiency (FE) and protein efficiency ratio were the lowest in fish fed the basal diet (P < 0.05). Body protein content was increased with the increasing iron levels (P < 0.05), but moisture, lipid and ash of fish were not significantly affected by dietary iron levels (P > 0.05). Activities of trypsin, lipase, α‐amylase, Na⁺, K⁺‐ATPase, alkaline phosphatase and gamma‐glutamyl transpeptidase were improved with increasing dietary iron levels. Serum iron were significantly enhanced with dietary iron levels up to 146.1 mg iron kg^?1 diet, and plateaued. In conclusion, iron improved digestive enzyme activities of juvenile Jian carp and the dietary iron requirement for serum iron of juvenile Jian carp (11.4–64.0 g) was 147.4 mg iron kg^?1 diet with ferrous fumarate as the iron source.     

Effects of dietary 60 g kg−1 dried distiller's grains in least‐cost practical diets on production and gut allochthonous bacterial composition of cage‐cultured fish: comparison among fish species with different natural food habits

Dried distiller's grain (DDG) is considered as an alternative ingredient of dietary feed due to its high contents of protein, fibre and fat. In this study, 60 g kg^‐1 of DDG was used to feed grass carp (Ctenopharyngodon idella), bluntnose black bream (Megalobrama amblycephala), gibel carp (Carassius gibelio) and black carp (Mylopharyngodon piceus) for 8 weeks, and its effect on fish production and gut allochthonous microbiota was investigated for the development of a suitable fish feed high in nutrients and low in cost for polyculture freshwater fish. DDG supplementation resulted in the less weight gain and higher feed conversion ratio of black carp (P < 0.05), but had no significant effects on other fish or parameters. PCR–denaturing gradient gel electrophoresis (DGGE) analysis indicated that all four fish species had some common and unique bacteria in their digestive tracts, and the gut microbiota of bluntnose black and gibel carp fed the control diet and DDG diets were very similar (Cs > 91%); of them, the total counts of intestinal bacteria studied by qPCR increased in grass carp (P < 0.05) and depressed in black carp (P < 0.05) when fed dietary DDG. Thus, we assumed that dietary DDG modulated production and gut microbiota of fish in a host‐specific way.