Effects of dietary compound acidifiers supplementation on growth performance and intestinal health of juvenile American eels (Anguilla rostrata) cultured in cement tanks

This experiment was conducted to investigate the effects of compound acidifiers (CAs) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata) cultured in cement tanks. Six cement tanks with similar fish size and weight (approximately 4 g/fish and 87 kg/tank) were randomly divided into control group and CAs group with three replicates each. The fish of two groups were fed commercial diet and commercial diet supplemented with 4 g/kg CAs, respectively. The trial period was 56 days. The dietary CAs supplementation significantly increased final fish weight, weight gain rate, specific growth rate and feed intake (P0.05). Protease activity in intestine was increased significantly by CAs supplementation (P0.05). CAs supplementation significantly increased the villi length and thickness of the intestinal muscular layer (P<0.05). Dietary CAs supplementation increased the richness and the diversity of intestinal microbiota. At the phylum level, the higher relative abundances of Proteobacteria, Actinobacteria and Bacteroidetes and the lower relative abundance of Firmicutes were observed in CAs group compared to the control group. At the genus level, dietary CAs supplementation significantly increased the relative abundances of Faecalitalea, Sphingomonas, Sutterella and Mycobacterium (P<0.05). In conclusion, the dietary 4 g/kg CAs supplementation might improve the growth performance and intestinal health of juvenile American eels cultured in cement tanks

Effects of <i>Macleaya cordata</i> Extract on Growth Performance, Serum Biochemical Parameters, and Intestinal Health of Juvenile American Eel (<i>Anguilla rostrata</i>)

The present trial was conducted to evaluate the supplementation effects of Macleaya cordata extract (MCE) on growth performance, serum biochemical parameters, and intestinal health of the juvenile American eel (Anguilla rostrata). The 480 juvenile American eels (10.93 ± 0.06 g) were randomly divided into four groups. They were fed on diets supplemented with MCE levels of 0, 25 mg/kg, 50 mg/kg, and 100 mg/kg for ten weeks, respectively. The 50 mg/kg or 100 mg/kg MCE could significantly improve growth performance, and increase the activities of acid phosphatase and alkaline phosphatase, as well as the level of high-density lipoprotein cholesterol. These levels of MCE also decreased the levels of D-lactate acid, triglyceride, and total cholesterol and the activities of aspartate aminotransferase, alanine aminotransferase, and diamine oxidase. The antioxidant ability, muscular thickness, and fold height of the intestine were enhanced by 50 mg/kg or 100 mg/kg MCE. There was no significant difference in the above parameters of groups fed with 50 mg/kg or 100 mg/kg of MCE. The beneficial effects on the intestinal microbiota were demonstrated in the group fed with 50 mg/kg MCE. In conclusion, the 50 mg/kg MCE could be used in the diet to improve the growth performance and health status of the juvenile American eels

Effect of Dietary Compound Acidifiers Supplementation on Growth Performance, Serum Biochemical Parameters, and Body Composition of Juvenile American Eel (<i>Anguilla rostrata</i>)

As growth-promoting feed additives, compound acidifiers (CAs) have been widely reported in many farmed fish species, whereas there is little information on the application of CAs in the eel diet. The present trial was conducted to evaluate the supplementation effects of CAs on growth performance, serum biochemical parameters, and body composition of the juvenile American eel (Anguilla rostrata). The CAs supplementation levels in the diet of American eel were 0, 2.0, 3.0, 4.0, and 5.0 g/kg, respectively. The trial lasted for 12 weeks. The most beneficial effects of CAs on promoting growth performance, decreasing levels of serum lipid, modifying parameters of the liver function and immune function in the serum, and increasing the utilization of calcium and phosphorus in the diet were observed in the fish fed with 4.0 g/kg CAs. Dietary CAs supplementation had no significant effects on the body composition of whole fish, whereas 5.0 g/kg of dietary CAs supplementation exerted negative effects on growth performance, serum biochemical parameters, and utilization of calcium and phosphorus. The recommended level of CAs in the diet was 3.5–3.7 g/kg to achieve the optimal weight gain and feed conversion ratio for the juvenile American eel

Effects of Macleaya cordata Extract on Growth Performance, Serum Biochemical Parameters, and Intestinal Health of Juvenile American Eel (Anguilla rostrata)

The present trial was conducted to evaluate the supplementation effects of Macleaya cordata extract (MCE) on growth performance, serum biochemical parameters, and intestinal health of the juvenile American eel (Anguilla rostrata). The 480 juvenile American eels (10.93 &plusmn; 0.06 g) were randomly divided into four groups. They were fed on diets supplemented with MCE levels of 0, 25 mg/kg, 50 mg/kg, and 100 mg/kg for ten weeks, respectively. The 50 mg/kg or 100 mg/kg MCE could significantly improve growth performance, and increase the activities of acid phosphatase and alkaline phosphatase, as well as the level of high-density lipoprotein cholesterol. These levels of MCE also decreased the levels of D-lactate acid, triglyceride, and total cholesterol and the activities of aspartate aminotransferase, alanine aminotransferase, and diamine oxidase. The antioxidant ability, muscular thickness, and fold height of the intestine were enhanced by 50 mg/kg or 100 mg/kg MCE. There was no significant difference in the above parameters of groups fed with 50 mg/kg or 100 mg/kg of MCE. The beneficial effects on the intestinal microbiota were demonstrated in the group fed with 50 mg/kg MCE. In conclusion, the 50 mg/kg MCE could be used in the diet to improve the growth performance and health status of the juvenile American eels

Grape seed proanthocyanidins alleviate the negative effects of dietary cadmium on pearl gentian grouper (Epinephelus fuscoguttatus female x Epinephelus lanceolatus male)

The present study was conducted to evaluate whether grape seed proanthocyanidins (GSPs) could alleviate the negative effects of dietary cadmium on growth performance, body composition, activities of digestive enzymes, and antioxidant potential in the intestine of pearl gentian grouper (Epinephelus fuscoguttatus female x Epinephelus lanceolatus male). Two hundred and forty pearl gentian groupers with the initial average body weight of 31.30±0.05 g/fish were randomly divided into four treatment groups with three replicates in each group and 20 fish in each replicate. The four treatment groups were identified as control group (the basal diet), Cd group (the basal diet+300 mg/kg Cd), Cd+GSPs group I (the basal diet+300 mg/kg Cd+400 mg/kg GSPs), and Cd+GSPs group II (the basal diet+300 mg/kg Cd+800 mg/kg GSPs group), respectively. The trial lasted for 42 days. Fish exposed to 300 mg/kg dietary cadmium had lower growth performance, mineral metabolism disorders with lower calcium and phosphorus levels, higher ash level, decreased lipase and protease activities, and antioxidant potential in the intestine. Dietary GSPs supplementation could counteract those negative effects to a certain extent. The alleviation effects of Cd+GSPs group II were better than those of Cd+GSPs group I. Except for calcium and phosphorus levels in whole fish composition, 800 mg/kg dietary GSPs supplementation could not recover the adverse effects caused by Cd stress. These results suggested that GSPs might potentially mediate dietary cadmium toxicity and alleviate the negative effects on pearl gentian grouper

Effects of White Fish Meal Replaced by Low-Quality Brown Fish Meal with Compound Additives on Growth Performance and Intestinal Health of Juvenile American Eel (<i>Anguilla rostrata</i>)

With a reduced supply and increased price of white fish meal (WFM), the exploration of a practical strategy to replace WFM is urgent for sustainable eel culture. A 70-day feeding trial was conducted to evaluate the effects of replacing WFM with low-quality brown fish meal (LQBFM) with compound additives (CAs) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata). The 300 fish (11.02 ± 0.02 g/fish) were randomly distributed in triplicate to four groups (control group, LQBFM20+CAs group, LQBFM30+CAs group and LQBFM40+CAs group). They were fed the diets with LQBFM replacing WFM at 0, 20%, 30% and 40%, respectively. The CAs were a mixture of Macleaya cordata extract, grape seed proanthocyanidins and compound acidifiers; its level in the diets of the trial groups was 0.50%. No significant differences were found in the growth performance between the control and LQBFM20+CAs groups (p > 0.05), whereas those values were significantly decreased in LQBFM30+CAs and LQBFM40+CAs groups (p p p > 0.05). The intestinal microbiota at the phylum level or genus level was beneficially regulated in the LQBFM20+CAs group; similar results were not shown in the LQBFM40+CAs group. In conclusion, with 0.50% CA supplementation in the diet, LQBFM could replace 20% of WFM without detrimental effects on the growth and intestinal health of juvenile American eels and replacing 30% and 40%WFM with LQBFM might exert negative effects on this fish species

Evaluation of Methanotroph (<i>Methylococcus capsulatus</i>, Bath) Bacteria Protein as an Alternative to Fish Meal in the Diet of Juvenile American Eel (<i>Anguilla rostrata</i>)

This study was conducted to evaluate the effects of replacing fish meal (FM) with methanotroph (Methylococcus capsulatus, Bath) bacteria protein (MBP) in the diets of the juvenile American eel (Anguilla rostrata). Trial fish were randomly divided into the MBP0 group, MBP6 group, MBP12 group, and MBP18 group fed the diets with MBP replacing FM at levels of 0, 6%, 12%, and 18%, respectively. The trial lasted for ten weeks. There were no significant differences in weight gain or feed utilization among the MBP0, MBP6, and MBP12 groups (except for the feeding rate in the MBP12 group). Compared with the MBP0 group, the D-lactate level and diamine oxidase activity in the serum were significantly elevated in the MBP12 and MBP18 groups. In terms of non-specific immunity parameters in serum, the alkaline phosphatase activity was significantly decreased in the MBP18 group, and the complement 3 level was significantly elevated in the MBP12 and MBP18 groups. The activities of lipase and protease in the intestine were significantly decreased in the MBP12 and MBP18 groups. Compared with the MBP0 group, the total antioxidant capacity and activities of superoxide dismutase, catalase, and glutathione peroxidase in the intestine were significantly decreased in the MBP18 group, while the malondialdehyde level was significantly increased. The villus height, muscular thickness, and microvillus density were significantly decreased in the MBP12 and MBP18 groups. There were no significant differences in the foresaid parameters between the MBP0 group and the MBP6 group. The intestinal microbiota of the MBP6 group was beneficially regulated to maintain similar growth and health status with the MBP0 group. The adverse effects on the intestinal microbiota were reflected in the MBP18 group. In conclusion, MBP could successfully replace 6% of FM in the diet without adversely affecting the growth performance, serum biochemical parameters, and intestinal health of juvenile American eels

Ground Effects and Stability Analysis of Airfoil Accelerated by Electromagnetic Propulsion

Aerospace vehicle launched by electromagnetic propulsion is a potential option for future reusable space transportation systems. Complex ground effects and stability issues are induced generally due to the introduction of electromagnetic levitation force. A dynamic model coupled with electromagnetic force and aerodynamic force was established for the two-dimensional wing (NACA0012). Numerical simulations were conducted on the flow characteristics, operational attitude, and aerodynamic characteristics of the wing during the Ma＝0~1.5 acceleration process. It indicates that ground effects can be divided into four stages. In the first stage, subsonic flows are presented on both the upper and lower wing surfaces, and there is basically no oscillation for the attitude and aerodynamic loads of the wing. In the second stage, transonic flow emerges on the upper wing surface, while the flow on the lower wing surface is dominated by a typical variable cross-section transonic flow accompanied by the transition from the choked flow mode to the unchoked one. In the third stage, the upper wing surface maintains transonic flows, while the lower wing surface undergoes choked flows which are fully expanded. In both the second and third stages, the wing attitude and aerodynamic loads oscillate significantly at low frequencies. In the fourth stage, the upper wing surface undergoes supersonic flows, while the lower wing surface maintains choked flows. The wing attitude and aerodynamic loads oscillate slightly at high frequencies. On this basis, the effects of suspension height, suspension stiffness and spacing between suspension magnets on the system stability were explored. It is found that increa-sing the suspension height is beneficial for improving system stability. Increasing the suspension stiffness or spacing between suspension magnets appropriately, while limiting the target speed of electromagnetic propulsion to be less than the critical Mach number of system oscillation divergence, is beneficial for significantly improving system stability

Feeding Strategies for Adapting Lake Sturgeon (Acipenser fulvescens) Larvae to Formulated Diets at Early Life Stages

Cost-effective feeding management is required to support conservation hatcheries for lake sturgeon (Acipenser fulvescens), an ecologically important species in the Great Lakes region. This study investigated an approach to transition lake sturgeon larvae from live feed (Artemia) to formulated feed and its effect on growth performance, survival, and response to acute hypoxia stress. The first experiment showed that sturgeon had similar (p &gt; 0.05) growth and survival when fed Artemia or the combined feeding of Artemia with the commercial diet (crude protein, 551 g/kg diet). Feeding solely on the commercial or lab-made (crude protein, 491 g/kg diet) diet significantly reduced growth and survival (p &lt; 0.05). In the second experiment, the growth performance of sturgeon (14 days post-hatch, DPH) fed with either Artemia only or combined feeding different feeding durations of two, three, and four weeks followed by a complete transition to the commercial diet. At the end of six weeks, the 3- and 4-week combined feeding periods resulted in significantly higher body weight and survival compared to the 2-week combined and the Artemia only feeding treatments. In the last experiment, sturgeons (27 DPH) were fed only with Artemia or combined feeding of Artemia with the commercial diet for four weeks followed by the complete transition to the commercial diet for two weeks. Eighteen fish from each treatment were investigated the response to acute hypoxic conditions (gradual decrease in dissolved oxygen level from 8 to 2.3 mg/L at the rate of 1 mg/L per hour). When the dissolved oxygen was between 3 and 4 mg/L, the mortality rate of the combination-fed sturgeon (11.7%) was significantly lower than those fed only Artemia (83.3%). These results clearly demonstrate that a commercial diet can partially replace Artemia at early life stages to improve growth, survival, and hypoxia tolerance and thus its co-feeding with Artemia is recommended

Effects of weaning American glass eels (Anguilla rostrata) with the formula diet on intestinal microbiota and inflammatory cytokines genes expression

This study aimed to investigate the effects of weaning American glass eels (Anguilla rostrata) with the formula diet on intestinal microbiota and the expression of inflammatory cytokines genes. During the feeding trial, the control group (termed IF group) was fed with initial feed for 34 days, and the experimental group (termed FF group) was fed with initial feed for 30 days, and then weaned with the formula diet for 4 days. After feeding trial, intestines were subjected to microbiota analysis using 16S rDNA high-throughput sequencing, and expression of three inflammatory cytokines genes in gut were examined by qPCR. The results indicated that the species richness and diversity of intestinal microbiota exhibited significantly higher in FF group than that in IF group (P < 0.05). At the phylum level, the core intestinal microflora was the same for two groups. The most abundant phylum was Firmicutes in IF group, while it was Proteobacteria in FF group. Five genera were significantly higher in the IF group compared with the FF group, and Bacillus was the most major enriched biomarker at genus level. Nine genera were significantly higher in the FF group compared with the IF group, and Acidovorax was the most major enriched biomarker. Weaning from initial feeding diet to formula feeding diet enhanced the expression levels of TNF-α and IL-8, and there was no significant change in IL-1β expression between the two groups. These findings would be very useful to improve the diet formulation for weaning stage of American glass eels