Abstract:To evaluate the feasibility of cottonseed protein in largemouth bass (Micropterus salmoides) diet, five isonitrogen-isolipid experimental diets (CPC₀ as control group, CPC₁, CPC₂, CPC₃, and CPC₄) were prepared by replacing 30% fish meal with 4 cottonseed proteins of different quality. Micropterus salmoides [average body weight (12.20±0.11) g] were fed in indoor circulating culture system for 8 weeks. The results showed that the nutrient composition, contents of gossypol, raffinose and stysaccharide of the four kinds of cottonseed proteins were different, and CPC₃ cottonseed protein quality was the best. The final body weight, weight gain rate and specific growth rate of CPC₃ group were significantly higher than those of the other groups, but there were no significant difference in the routine nutrients and muscle amino acid nutritional composition among all groups. The activities of SOD and GSH-Px and the mRNA expressions of CAT and SOD in liver of CPC₃ group were the highest, while the content of MDA was the lowest. The relative expressions of anti-inflammatory factors IL-10 and TGF-β were the highest in CPC3 group, while the relative expressions of pro-inflammatory factors IL-1β, IL-8 and TNF-α were the lowest in CPC₃ group. In addition, cottonseed protein sources could significantly affect the liver protein metabolism of largemouth bass, and the activities of ALT and AST and the expression levels of P13K, Akt, m-TOR, S6K1 and 4E-BP in CPC₃ group were the highest. Meanwhile, it was found that CPC₃ group had the highest intestinal T-SOD enzyme activity, the lowest MDA content, and the lowest intestinal permeability indexes (diamine oxidase, D-lactic acid and endotoxin). Cottonseed protein sources also affected the expression of tight junction protein-related genes ZO-1, Claudin-1 and Occludin in the intestine. The results showed that different cottonseed protein quality had different effects on the growth and health of M. salmoides, among which cottonseed protein CPC₃ showed the best effect and significantly improved the liver and intestinal health of M. salmoides, thereby promoting the growth of M. salmoides. Cottonseed protein CPC₃ can be used as a good protein source for M. salmoides feed.

Abstract:To determine the dietary zinc requirement of juvenile largemouth bass (Micropterus salmoides), casein, gelatin and fish meal were used as the main protein sources and ZnSO₄·H₂O as zinc source to produce a semi-purified diet. Then, zinc was added into the basal diet at levels of 0, 25, 50, 100 and 200 mg/kg, to obtain five diets containing zinc of 24.8, 48.8, 78.9, 126.1 and 223.6 mg/kg dry matter, respectively. Largemouth bass with initial body mass of (10.99±0.07) g were fed one of the five diets for 8 weeks. The results showed that the supplementation of 25 mg/kg Zn significantly increased the weight gain rate (WGR), and reduced feed coefficient ratio (FCR) of largemouth bass, which tended to stabilize when higher levels of Zn were added. When dietary Zn reached 25-49 mg/kg, the serum activity of CuZn-SOD and T-SOD remained stable, while Zn-79 group showed the highest AKP activity. The zinc content in whole fish and vertebrae increased with the increasing dietary Zn, and showed no significant increase when dietary Zn content was higher than 126 mg/kg (Zn-126 group). The iron content in whole body, iron and manganese contents in vertebra, and the retention of iron and zinc in whole body decreased with the increasing dietary Zn. In conclusion, the supplementation of Zn in diet improved the weight gain and feed utilization, promoted serum immunity and Zn deposit in whole body and vertebra. Based on the WGR, FCR, whole body zinc and vertebra zinc, the broken-line analysis indicated that the dietary requirement of Zn was 45.5, 44.6, 121.8 and 130.5 mg/kg dry matter, respectively.

Abstract:In the past several decades, the rapid development of aquaculture has brought many environmental problems. The waste discharged from aquaculture may lead to eutrophication and deterioration of water quality, which will further affect the growth and health of aquatic animals. A new aquaculture model is emerging to deal with this problem, named in-pond “raceway” aquaculture system. Based on that, a comparative study on the nutritional value and volatile flavor compounds profile in muscle of Culter alburnus was conducted to investigate the difference between in-pond “raceway” aquaculture system and traditional pond culture. Amino acids analyzer, high performance liquid chromatography (HPLC) and gas chromatograph-ion mobility spectrometer (GC-IMS) were used to identify and analyze the profile of amino acids, fatty acids and volatile flavor compounds in the muscle under different culture conditions. The fingerprint spectra of volatile flavor compounds were established. There was no significant difference in the content of crude protein and crude lipid of muscle between the two groups. The content of essential amino acids [EAA, (8.54±0.01) g/100 g wet basis] and total amino acids [TAA, (17.36±0.00) g/100 g wet basis] of muscle in the in-pond “raceway” group was significantly increased. Additionally, a total of 23 volatile flavor compounds were screened from the C. alburnus muscle from the two groups. Compared with the traditional pond culture group, the contents of butanal, 3-methylbutanal, 2-methylbutanal, pentanal, heptanal, benzaldehyde, octanal, nonanal, 2-butanone, 3-hydroxy-2-butanone and ethanol were decreased, while the contents of 2-heptanone, 1-hexanol and 1-octen-3-ol were increased in the in-pond “raceway” aquaculture system group. At the same time, compared with traditional pond culture group, the volatile flavor of the in-pond “raceway” aquaculture system group improved due to the decrease of some unpleasant volatile flavor compounds. C. alburnus cultivated in the in-pond “raceway” aquaculture system improved the amino acid and flavor characteristics and kept the muscle approximate composition unchanged. The above results provide basic data for the evaluation of the flesh quality of C. alburnus of the in-pond “raceway” aquaculture system, which indicates that this model has great potential for improvement of fish quality.

Abstract:The trial was conducted to study the effects of dietary zinc (Zn) on growth, non-specific immune indexes, disease resistance and intestinal flora structure in juvenile Litopenaeus vannamei. Zinc sulfate heptahydrate (ZnSO₄·7H₂O) was used as the Zn source in this experiment. The healthy prawns [initial body weight (0.45±0.01) g] were fed diets (isonitrogenous and isolipid) containing available Zn levels (i.e., 0, 20, 40, 60, 80, 100, and 150 mg/kg) for 8 weeks, respectively. The results showed that: ① The weight gain rate (WGR) and specific growth rate (SGR) in the 60 mg/kg group were significantly higher than those in the control group, and the best feed conversion rate (FCR), the optimal protein efficiency ratio (PER) and survival rate (SR) were found in 80 mg/kg group.② The crude lipid (CL) contents in 80-150 mg/kg groups were significantly higher than that in control group, and the contents of crude ash (CA) in 40-80 mg/kg groups were significantly higher than that in control group.③ The contents of serum total protein (TP), total cholesterol (TC) and triglyceride (TG) in Zn supplemented groups were significantly higher than those in control group. ④ Dietary Zn supplement increased the activities of serum superoxide dismutase (SOD), phenol oxidase (PO), alkaline phosphatase (AKP) and acid phosphatase (ACP) and total antioxidant capacity (T-AOC), and significantly decreased the content of malondialdehyde (MDA) in serum, indicating that Zn could improve the non-specific immunity of L. vannamei.⑤ In the experiment of artificial acute infection with Vibrio harveyi, the survival rate of shrimp increased firstly and then decreased with the increase of Zn levels. The survival rate in Zn supplemented group was significantly higher than that in control group, and the highest survival rate and disease resistance were found in 80 mg/kg group. ⑥ In the analysis of intestinal flora, the numbers of effective OTUs in 40 mg/kg and 100 mg/kg groups were significantly higher than that in control group. With the increase of dietary Zn, the Ace index and Chao1 index increased significantly, while the Shannon index and Simpson index had no significant changes. The results showed that an optimal level of Zn could promote the growth and improve the disease resistance of juvenile L. vannamei. The growth performance and disease resistance of L. vannamei were poor when Zn was deficient in diets, while excessive Zn level inhibited the growth of L. vannamei to a certain extent. Overall, based on the WGR, the growth performance of L. vannamei was significantly improved by supplementing 94.46 mg/kg Zn to the diets. Based on the evaluation of disease resistance, the optimal dietary Zn supplement of L. vannamei was 80 mg/kg.

Abstract:The marked increase in the metabolic rate that occurs following feeding is commonly referred to as specific dynamic action (SDA). Previous studies on SDA in animals have found that the meal type, temperature, body size, feeding frequency, fasting and feeding rate all have significant effects on SDA. The study of postprandial metabolic response in Percocypris pingi has not been reported. To investigate the effects of temperature and feeding rate on postprandial metabolic traits in juvenile P. pingi, the experimental fish [body weight: (38.35±0.49) g, body length: (14.22±0.10) cm] were fed with loach (Misgurnus anguillicaudatus) (feeding rates: 1%, 2%, 4% body mass at 15 ℃; 1%, 2%, 4% and 6% body mass at 25 ℃) for 4 weeks as diet acclimation at 15 ℃ and 25 ℃ in indoor recirculating aquaculture systems. After that, the oxygen consumption rate was detected and parameters related to postprandial metabolic response were calculated. Results showed that at the same feeding rate, resting metabolic rate, peak metabolic rate, total energy expenditure on SDA and SDA coefficient of 25 ℃ acclimation group were significantly higher than those of 15 ℃ acclimation group. The SDA duration of 25 ℃ acclimation group at 2% and 4% feeding rate was significantly shorter than that of 15 ℃ acclimation group. At the 25 ℃, fish of higher feeding rates (4% and 6%) presented significantly higher peak metabolic rate, factorial metabolic scope, SDA duration and total energy expenditure on SDA than those of lower feeding rates (1% and 2%) at 25 ℃, and times to peak metabolic rate of 4% and 6% feeding rates were significantly earlier than that of 1% and 2% feeding rates as well. However, the SDA coefficient showed an opposite situation: higher feeding rate presented significantly lower values. At the 15 ℃, peak metabolic rate, factorial metabolic scope, SDA duration and energy expended on SDA of 4% feeding rate group were significantly higher than those of 1% and 2% feeding rates. Nevertheless, no significant difference in the time to peak metabolic rate and the SDA coefficient among all feeding rates were observed at 15 ℃. All the above information suggested that the water temperature of 25 ℃ is more beneficial to the rapid food digestion and absorption by juvenile P. pingi; and the fish may meet the increased energy demand during digestive process by means of increasing peak metabolic rate and prolonging SDA duration with the increase of feeding rate. The results of this study may provide important reference data for the breeding practice and species protection of P. pingi.

Abstract:Bile acids play an important role in glucose metabolism, lipid metabolism, and they can also help to maintain the liver health and intestinal homeostasis in animals. In recent years, bile acids have been widely used as new additives in aquatic feeds. However, so far, most of the bile acid products used in aquaculture are mixed bile acids. There are many different kinds of bile acids, and different bile acids have different effects on the growth and metabolism of fish. Therefore, it is necessary to evaluate the effects of different bile acids on fish growth and metabolism to select the appropriate type of bile acids for precise nutritional regulation. This experiment was conducted to evaluate the effect of sodium deoxycholate as a feed additive on Micropterus salmoides. Two experimental diets were formulated to contain different sodium deoxycholate levels of 0, and 300 mg/kg referred to as CON and SD, respectively. The effects of sodium deoxycholate on the growth condition, metabolic characteristics and intestinal microbiota were analyzed. M. salmoides (10.80 ±0.12) g were cultured for 8 weeks. The results showed that sodium deoxycholate significantly increased the final body weight [(37.24 ±0.64) g in the control group and (46.87 ±1.44) g in the sodium deoxycholate group]. The body length was (12.42 ±0.12) cm in the control group and (13.07 ±0.14) cm in sodium deoxycholate group. The condition factor (CF) was (1.95 ±0.06) g/cm³ in the control group and (2.09 ±0.03) g/cm³ in the sodium deoxycholate group, but there was no significant difference in viscera index (VSI) or hepatosomatic index (HSI). Sodium deoxycholate had no effect on the total lipid and crude protein of whole fish. Sodium deoxycholate significant increased the expression level of gluconeogenesis-related and glycolysis-related genes in liver and muscle, and the sodium deoxycholate promoted the glycogen accumulation in muscle [(0.31 ±0.03) mg/g in control group and (0.46 ±0.03) mg/g in sodium deoxycholate group] by increasing the activity of glycogen synthase, but there was no significant difference in the liver glycogen content between these two groups. In addition, sodium deoxycholate significantly increased bile acids content in gallbladder [(199.4 ±12.72) μmol/L in control group, (341.1 ±8.52) μmol/L in sodium deoxycholate group]. Our results indicated that sodium deoxycholate can promote the bile acid synthesis mainly by down-regulating the expression level of fxr gene and up-regulating the expression level of cyp7a1 gene in the liver. The abundance of Firmicutes and Bacteroidetes decreased while Actinobacteria increased in M. salmodides fed with sodium deoxycholate at the phylum level. All these results suggested that sodium deoxycholate can be used as a feed additive for M. salmodides to promote the growth condition, and increase muscle glycogen accumulation and bile acid synthesis.

Abstract:The grass carp (Ctenopharyngodon idella) dietary Schizochytrium sp. stearin oil may show better growth performance than dietary fish oil by saving energy required for de novo synthesis of DHA, promoting lipolysis energy supply and inhibiting protein catabolism. The purpose of this study was to investigate whether DHA-rich Schizochytrium sp. stearin oil needs to be compatible with EPA and its possible mechanism. Equipped with five groups of iso-nitrogen and isoenergetic diets and fed grass carp (22.70 g±0.80 g) for 49 d. The 0.52% n-3 long-chain polyunsaturated fatty acid (LC PUFA) of the diets were provided with fish oil (F-O); Sc stearin oil (S-O); stearin oil (DHA)∶EPA =3∶2 (SE1-O); stearin oil (DHA)∶EPA = 1∶1(SE2-O); EPA (E-O), respectively. The results showed: 1) There was no difference in the weight gain rate (WG), specific growth rate (SGR) and feed conversion ratio (FCR) among all the groups; 2) The content of crude protein in muscle of S-O group was significantly higher than those of E-O group; 3) the content of DHA in muscle of S-O group was significantly higher than that of F-O group, SE1-O group and E-O group; 4) there was no significant difference in atherogenicity index among the groups, the thrombogenicity index of SE2-O group was significantly higher than that of F-O group, the hypocholesterolemic/ Hypercholesterolemic ratio in S-O group and SE2-O group was markedly lower than those in F-O group; 5) the adipose size of intraperitoneal fat in E-O group was notably higher than those in F-O group and SE1-O group, the adipose TAG lipase(ATGL)and carnitine palmitoyltransferase 1(CPT1) mRNA levels in E-O group were apparently down-regulated; in muscle, the fatty acid desaturase (FAD)mRNA level was markedly higher in E-O group than that in S-O group, the fatty acid elongase(ELO)mRNA level was obviously down-regulated in S-O group. Studies have shown that the use of Sc oil alone or in combination with EPA had no significant effect on growth, n-3LC PUFA content and lipid hydrolysis of adipose tissue of grass carp. When EPA was the sole source of n-3LC PUFA, the lipid hydrolysis of adipose tissue was reduced and the content of crude protein in muscle was reduced. High level of DHA in the diet would weaken the body's ability to synthesize LC PUFA. Compared to EPA, grass carp may need DHA more, and the Sc oil could be used alone in the feed of grass carp without combination with EPA.

Abstract:In order to study the effects of Bacillus subtilis HGcc-1 on the gut and liver health, serum complement and gut microbiota of Cyprinus carpio fingerlings, healthy C. carpio fingerlings with a body weight of (13.10±0.39) g were selected, and randomly divided into HGcc-1 supplementation group and control group, and after 20 weeks of feeding, the growth indicators were measured, and the C. carpio serum endotoxin (LPS), Alanine aminotransferase (ALT), Aspartate aminotransferase (AST), total complement and lysozyme were detected, and 16S rRNA sequencing of the gut microbiota was made. At the same time, the gut microbiota induced by HGcc-1 supplement group and the control group were transferred to germ free Danio rerio, and then the levels of endotoxin binding protein (LBP), ALT and AST and the expression levels of C3 and C4 genes of germ free D. rerio were measured; finally, the levels of ALT and AST and the expression levels of C3 and C4 genes in germ free D. rerio were tested when HGcc-1 directly acted on germ free D. rerio. The results showed that HGcc-1 had no effect on the weight gain rate of C. carpio, but adding HGcc-1 significantly reduced the level of serum endotoxin, ALT and AST. The serum total complement level of the HGcc-1 supplement group was significantly increased, compared with control group. The 16S rRNA sequencing results showed that at the phylum level, the HGcc-1 supplement diet group increased the abundance of Fusobacterium by 47.1% compared to control group; the abundance of Proteobacteria was decreased by 70.7% compared with the control group; at the genus level, the HGcc-1 supplement diet group increased the abundance of Cetobacterium by 47.1% compared with the control group; the abundances of Citrobacter and Aeromonas were reduced by 56.6% and 70.9% respectively, compared with the control group. And it was further observed that the intestinal microbiota of HGcc-1 addition group decreased the content of endotoxin binding protein (LBP) and level of AST of the germ free (GF) D. rerio, and significantly increased the gene expression of complement component 3 and the complement component 4 (C3 and C4) of the GF D. rerio. At the same time, the direct interaction between HGcc-1 and GF D. rerio also decreased the ALT and AST levels of the GF D. rerio. This study shows that dietary B. subtilis HGcc-1 can improve the gut and liver health, serum complement and intestinal microbiota homeostasis of C. carpio fingerlings. This study laid a theoretical foundation for the further application of B. subtilis HGcc-1.

Abstract:To explore the mechanism of peroxisome proliferator activated receptor γ coactivator 1α (PGC1α) in the glucose metabolism of blunt snout bream Megalobrama amblycephala, the partial cDNA of PGC1α was cloned, and the transcriptional response of this gene to nutrient restriction, carbohydrate-enriched diets and glucose loadings were investigated. The partial cDNA was 2566 bp with an open reading frame of 1 404 bp encoding 467 amino acids, and compared to Ctenopharyngodon idellus, it showed 96.79% homology. The mRNA levels of PGC1α in the brain and liver were significantly increased during 10 days of fasting, and then decreased to normal level after refeeding 1 h. The high-carbohydrate diet significantly decreased the mRNA levels of PGC1α in the brain and liver. In addition, the mRNA levels of PGC1α in the brain and liver both decreased significantly during the first 2 h, then returned to the basal value at 12 h. The results indicated that PGC1α plays an important role in glucose metabolism in M. amblycephala. The results obtained here will provide the theoretical foundation for completing the research of PGC1α functions involving the regulation of glucose homeostasis in fish.

Abstract:In order to study the effects of lactic acid bacteria (LAB) on the growth, antioxidative status and immunity of Channa argus, 360 C. argus with an initial weight of (3.43 ±0.05) g were selected and randomly divided into 4 groups. Each group was set up with 3 replicates, each with 30 C. argus. They were fed with basic feed and test feed supplemented with 10⁸ CFU Lactococcus lactis L21 (L21 group), Lactobacillus plantarum W21 (W21 group), and Enterococcus faecalis L2 (L2 group). After 8 weeks, we collected the serum, liver, spleen, kidney and intestinal tissues to determine related indicators and genes expression. The results showed that compared with the control group, the three LAB added to the feed could significantly increase the average weight gain rate (AWGR), specific growth rate (SGR) and feed efficiency rate (FER) of C. argus, and the L21 group was significantly higher than other groups. Compared with the control group, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and alkaline phosphatase (AKP) in the L2 group were significantly higher than control group, the lysozyme (LZM) activity of the W21 and L2 groups was significantly higher than that of the control and L21 groups, and the immunoglobulin M (IgM) activity of each group was not significant. The genes expression levels of IL-1β, IL-8, IL-10 and TNF-α in various tissues all increased to varying degrees, and LAB could significantly promote the expression of immune-related genes in the intestine. Research shows that under the experimental conditions, L. lactis L21 had the best application effect in C. argus, and it could improve the growth, and immune function of C. argus.

Abstract:Water temperature and dietary phosphorus levels are crucial for the growth of crustaceans. However, the interactions between both factors are still poorly understood in crustacean culture, which brings difficulties in advancing the feed utilization. This experiment was conducted to explore the effects of different temperature and dietary phosphorus levels on the production performance, tissue and water phosphorus content of M. nipponense. Using a 3×3 factorial design, nine groups (respectively named 20/1.1, 20/1.5, 20/1.9, 25/1.1, 25/1.5, 25/1.9, 30/1.1, 30/1.5, 30/1.9) were formed, including three water temperature (20, 25 and 30 ℃) and three dietary phosphorus levels (1.1%, 1.5% and 1.9%). Each diet was tested by 4 replicates. Prawns were reared in the indoor circulation systems for 8 weeks. The results showed that, in terms of water temperature, the final body weight (FBW), specific growth rate (SGR) and weight gain rate (WGR) of the 30 ℃ group were all significantly higher than those of the 20 ℃, but showed no statistical difference with those of the 25 ℃. However, the opposite was true for feed intake and feed conversion rate (FCR). In addition, the phosphorus retention efficiency (PRE) and hemolymph phosphorus levels of the 30 ℃ group were both significantly higher than those of the other two groups, meanwhile the hemolymph phosphorus level of this group was significantly higher than that of the 25 ℃ group, but showed no significant difference with the 20 ℃ group. In terms of dietary phosphorus levels, the FBW, WGR, PRE and hemolymph calcium level of the 1.9% phosphorus level group were all significantly lower than those of the other groups, while phosphorus intake and FCR showed the opposite trend. The SGR of the 1.9%phosphorus level group was significantly lower than that of the 1.5% group, but showed no statistical difference with that of the 1.1% group. Besides, the whole-body phosphorus contents of the 1.1% group was significantly lower than that of the other groups, and the hemolymph calcium content of this group was significantly higher than that of the 1.9% group, but there was no significant difference with the 1.5% group. Serum alkaline phosphatase (AKP) activities of the 1.5% group was significantly higher than that of the 1.1% group, but showed no statistical difference with those of the1.9% group. Furthermore, feed intake, phosphorus intake, PRE, hemolymph phosphorus level and AKP activities were all significantly affected by the interaction between water temperature and dietary phosphorus level with the maximized values observed in the 20/1.1, 25/1.9 and 30/1.9, 30/1.1, 30/1.9, 25/1.5 group, respectively. Additionally, water phosphorus levels increased significantly with increasing sampling time, while the water phosphorus level of the 20/1.5 group was significantly higher than those of the 25/1.1 and 30/1.1 groups. Overall, M. nipponense in the 30/1.1 group obtained the best growth performance and feed efficiency coupled with low phosphorus emission.

Abstract:An experiment was conducted to study the effect of aflatoxin B1 on growth performance, digestive enzyme activities in intestinal tract and liver function of juvenile Pelteobagrus fulvidraco. Four experimental diets were prepared to contain 0 (control), 50, 100, 200 μg/kg aflatoxin B1. Each diet was randomly assigned to triplicate cages of 50 fish with an initial average weight of (6.00±0.10) g for 8 weeks. The results showed that: ① There were no significant differences in survival rate, feed coefficient ratio and specific growth rates of juvenile Pelteobagrus fulvidraco among all groups. The activity of trypsin in the AFB1 group significantly increased compared with the control group. When the AFB1 concentration reached 100 and 200 μg/kg, the amylase and lipase activities significantly decreased; ② With increasing AFB1 concentration, the levels of aspartate aminotransferase(AST), alanine aminotransferase(ALT), glucose, triglyceride, total bile acid and total cholesterol contents in serum significantly increased, and the AST, ALT activities in the liver significantly decreased; ③With increasing AFB1 concentration, the catalase activity and malondiadehyde content in the liver significantly increased. The superoxide dismutase activity significantly increased when the AFB1 concentration reached 100 and 200 μg/kg; ④ With increasing AFB1 concentration, the expression levels of sod and il-1β in the liver were significantly up-regulated, the expression levels of cat, il-10 and il-8 in the liver were significantly up-regulated when the AFB1 concentration reached 200 μg/kg; ⑤ Histological observations showed that an increase in the concentration of AFB1 caused some liver cells to present slight atrophy, hepatocyte nucleus shifted, cell boundary blurred, liver cell vacuolation degre. The results showed that under the experimental conditions, there was no significant effect on the growth of juvenile Pelteobagrus fulvidraco with the concentration of AFB1≤200 μg/kg, but it could affect the digestion and absorption function of the intestines, cause oxidative stress and inflammatory reactions in the liver, and result in liver function damage with the concentration of AFB1≥50 μg/kg.

Abstract:An 8-weeks feeding trial was conducted to investigate the effects of dietary calcium/phosphorus ratios on the growth performance, minerals bioaccumulation, and energy metabolism in juvenile swimming crab (Portunus trituberculatus). Five semi-purified experimental diets were formulated to contain different ratios of calcium to phosphorus (1.00∶2.00, 1.00∶1.50, 1.00∶1.00, 1.00∶0.75 and 1.00∶0.50, respectively). A total of 150 swimming crab juveniles [initial weight (12.82 ±0.37) g] were randomly allocated into five groups with three replicates, each and consisted of 30 crabs. The results indicated that crabs fed the diets with calcium to phosphorus ratios of 1.00∶1.00 and 1.00∶0.75 had significantly higher specific growth rate (SGR) and feed efficiency (FE) than those fed the other diets. The highest activity of GOT in hemolymph was observed at crabs fed the diet with calcium to phosphorus ratio of 1.00∶0.50, and AKP and GPT exhibited an increasing trend with the increase of dietary calcium to phosphorus ratios. Moreover, the content of phosphorus in tissues significantly increased with dietary calcium to phosphorus ratios decreasing from 1.00∶0.50 to 1.00∶2.00. Furthermore, the highest ATP content in hepatopancreas was observed in crab fed the diets calcium/phosphorus ratios of 1.00∶1.50 and 1.00∶1.00. The activities of enzymes such as hexokinase (HK) and succinate dehydrogenase (SDH) related to energy metabolism were significantly higher in hepatopancreas of crabs fed the diet with calcium to phosphorus ratio of 1.00∶1.00. Crabs fed the diet containing calcium to phosphorus ratio 1.00∶1.00 also showed significantly higher expression of genes involved in electron transport chain complex, such as nd1, sdhc, cytb and cox Ⅱ than those fed the other diets. The genes related to mitochondrial energetic metabolisms, such as atpase6, sirt3, and nrf1 were significantly up-regulated in crabs fed the diet with calcium and phosphorus ratio of 1.00∶0.75. Overall, based on broken-line and quadratic regression analysis between PWG against dietary calcium to phosphorus ratios, the optimal dietary calcium to phosphorus ratio was estimated to be 1.06-1.26, and this range could be recommended to maintain optimal phosphorus bioaccumulation and promote energy production for juvenile swimming crab.

Abstract:Mandarin fish (Siniperca sp.) is a valuable freshwater economic fish in China, and its production has approached 330000 tons in 2019. This paper introduced aquaculture situation of Siniperca sp. from three aspects, including aquaculture status, aquaculture mode and selective breeding. The feeding habit of Siniperca sp. is unique, which relies on prey fish for lifetime. For many years, prey fish are mainly used to feed Siniperca sp., and the way of raising fish by fish not only causes the waste of fishery resources, but also aggravates the damage to environment and resources. Thus, the paper also summarized the external factors affecting feeding characteristics of Siniperca sp. species from environmental factors and feed properties, and analyzed the internal factors from the aspects of feeding sense organs and feeding regulation factors. This may be helpful to adjust the feeding habits of Siniperca sp. through artificial intervention, and provide necessary basis for its conversion to eat formula feed. Additionally, it is necessary to strengthen the research on the feeding regulation mechanism and nutritional physiological demand characteristics, so as to achieve the breakthrough of compound feed and promote the green and healthy development of its aquaculture industry.

Abstract:The purpose of this study was to investigate the arginine requirement and effects of dietary arginine levels on the growth and metabolism of turbot (Scophthalmus maximus). Turbots with an initial body weight of (43.07±0.10) g were selected as the research object. Five isonitrogenous and isolipid diets (51% crude protein and 12.5% crude lipid) were formulated with casein and gelatin as the main protein sources and fish oil and soybean lecithin as the lipid sources. The arginine contents of the diets were 1.92%, 2.65%, 3.40%, 4.17% and 4.88% of dry matter by adding crystalline amino acid mixture, respectively. (The corresponding diet number was 1, 2, 3, 4 and 5, respectively). The group fed 1.92% arginine level diet served as control group. Each treatment was set to 3 replicates, each containing 12 fish, and the breeding period was 10 weeks. The results showed that 3.40% to 4.88% arginine (6.66% to 9.52% of dietary protein) significantly improved the growth performance and feed utilization of turbot compared with the control group. According to the broken line regression analysis based on specific growth rate (SGR), the optimal dietary arginine requirement of turbot was estimated to be 3.17% of dry matter (6.21% of dietary protein). Appropriate dietary arginine levels significantly increased body protein content and plasma total protein level, while significantly decreased plasma glucose level. In addition, appropriate dietary arginine levels significantly enhanced the expression of genes related to fatty acid synthesis, fatty acid β-oxidation, glycolysis, tricarboxylic acid (TCA) cycle and oxidative phosphorylation, while significantly decreased the expression of genes associated with amino acid degradation in liver. The results demonstrated that 3.40% to 4.88% arginine (6.66% to 9.52% of dietary protein) can regulate the nutrient metabolism and promote the growth of turbot.