Molecular cloning,characterization, tissue expression and nutritional regulation of O‐GlcNAc transferase gene in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

O‐GlcNAc transferase gene (OGT) was considered as the sole rate‐limiting enzyme in the O‐GlcNAc modification. In the present study, the OGT gene of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) was cloned and characterized, and its expression in response to dietary carbohydrate level and acute glucose treatment was investigated. The full‐length of OGT (GenBank accession no. KY656469 ) was 4,063 bp, including a 302 bp 5′untranslated terminal region (UTR), a 3,165 bp coding region that encoded 1,054 amino acids residues and a 596 bp 3′ UTR. The highly conservation of OGT gene between fish and mammals was also observed through multiple sequences alignment and phylogenetic analysis. O‐GlcNAc transferase gene was ubiquitously expressed in all detected tissues with highest expressions in brain and liver, to a lesser degree, in eye, heart, kidney and intestine. The increasing dietary carbohydrate from 8.02% to 16.08% had no significant effect on the mRNA expression of OGT. However, the expression of OGT was slightly elevated at 6 hr post‐glucose injection, and the elevation became significant at 24 hr time‐point. These data may enhance our understanding on the nutritional regulation of OGT and O‐GlcNAc modification in fish species.     

Effects of dietary carbohydrate to lipid ratio on growth,feed utilization,body composition and digestive enzyme activities of golden pompano (Trachinotus ovatus)

An 8‐week feeding trial was conducted to investigate the effects of dietary carbohydrate to lipid ratio (CHO: L) on growth, feed utilization, body composition and digestive enzyme activities of golden pompano, Trachinotus ovatus. Five iso‐nitrogenous (450 g/kg protein) and iso‐energetic (19 MJ/kg gross energy) diets with varying CHO: L ratios of 0.68, 1.02, 1.62, 2.61 and 4.35, respectively, were fed to triplicate groups of 30 fish (average 13.8 ± 0.1 g). Results showed that dietary CHO: L ratios did not show any significant influence on survival of golden pompano (p > .05) but significantly affected its growth performance and feed utilization (p < .05). Fish fed diets with CHO: L ratios at 1.62 and 2.61 exhibited the highest final body weight, weight gain ratio, specific growth rate, feed efficiency ratio and protein efficiency ratio. Fish body lipid and liver glycogen contents were also significantly influenced by CHO: L ratio (p < .05). Hepatic amylase activity increased firstly and then decreased as the dietary CHO: L ratio increased, while lipases activity decreased with increasing dietary CHO:L level. The regression model analysis showed that the most suitable dietary CHO: L ratio (protein 450 g/kg) to reach the highest weight gain ratio is 2.38.     

Response of facilitative glucose transporter 1 to salinity stress and dietary carbohydrate nutrition in white shrimp Litopenaeus vannamei

Facilitative glucose transporter 1 (GLUT1) is a transporter protein for glucose transport via the plasma membrane of the cells to provide energy through carbohydrate metabolism. GLUT1 cDNA from Litopenaeus vannamei was obtained and analysed in this study. Full‐length GLUT1 cDNA is 2062 bp long and contained a 1506‐bp ORF encoding a 502 amino acid protein, a 270‐bp 5′UTR and a 284‐bp 3′UTR. When shrimp were under acute low salinity stress, the expression in hepatopancreas, muscle, gill and eyestalk was all up‐regulated at 12 h (P < 0.05) and 96 h (P < 0.05), while the expression in the four tissues was all down‐regulated at 6 h (P < 0.05) and 48 h (P < 0.05) . The expression in the muscle of shrimp at water salinity of 3 was lower than that at water salinity of 30 independent of dietary carbohydrate levels, while expression in hepatopancreas, gill and eyestalk was up‐regulated at 200 and 300 g kg^?1 carbohydrate levels. The expression in all tissues fed glucose was up‐regulated when compared to the expression in shrimp held at a water salinity of 30. This study suggests that GLUT1 is a conserved protein in L. vannamei, and changes in expression due to environmental salinity and dietary carbohydrate level and source.     

Effects of different dietary lipid sources on growth performance,body composition and lipid metabolism‐related enzymes and genes of juvenile golden pompano,Trachinotus ovatus

Three groups of juvenile golden pompano, Trachinotus ovatus (54.75 ± 0.25 g), were each fed one of three diets containing different lipid sources: fish oil (FO), soybean oil (SO) and lard oil (LO). Fish were reared in sea cages for 8 weeks, and the fish fed the FO diet had significantly higher specific growth rate (SGR) but lower condition factor (CF) than the other treatments. The fatty acid (FA) composition of whole‐body lipids was closely correlated with those in the diets. Although no differences can be found in hepatic fatty acid synthase (fasn) activity, the carnitine palmitoyl transferase 1 (cpt1) activity in fish fed the FO diet was significantly higher compared with other treatments. In addition, the relative gene expression of lipid metabolism‐related enzymes, such as cpt1, fas, apolipoprotein B100 (apoB100), delta‐6 fatty acyl desaturase (fadsd6) and fatty acid‐binding protein 1 (fabp1), was also influenced by the different dietary lipid sources. Serum triglyceride (TG) and glucose content in fish fed the LO and FO diets were significantly higher than those in the SO group. Accordingly, it can be concluded that FO could not be completely replaced by SO or LO in golden pompano diets. The lipid sources of a diet could impose significant influence on body condition factor and hepatic lipid metabolism of golden pompano.     

Effect of dietary carbohydrate sources on growth performance and utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Günther)

The nutritional function of monosaccharides, disaccharides and polysaccharides for omnivorous gibel carp and carnivorous Chinese longsnout catfish were investigated and the ability of these two species to utilize carbohydrates was compared. For each species, triplicate groups of fish were assigned to each of five groups of isoenergetic and isonitrogenous experimental diets with different carbohydrate sources: glucose, sucrose, dextrin, soluble starch (acid‐modified starch) and α‐cellulose. The carbohydrates were included at 60 g kg^?1 in Chinese longsnout catfish diets and at 200 g kg^?1 in gibel carp diets. A growth trial was carried out in a recirculation system at 27.8 ± 1.9 °C for 8 weeks. The results showed that fish with different food habits showed difference in the utilization of carbohydrate sources. For gibel carp, better specific growth rate (SGR) and feed efficiency (FE) were observed in fish fed diets containing soluble starch and cellulose, but for Chinese longsnout catfish, better SGR and FE were observed in fish fed diets containing dextrin and sucrose. Apparent digestibility coefficient of dry matter (ADC_d) and apparent digestibility coefficient of energy (ADC_e) were significantly affected by dietary carbohydrate sources in gibel carp. ADC_d and ADC_e significantly decreased as dietary carbohydrate complexity increased in Chinese longsnout catfish except that glucose diet had medium ADC_d and ADC_e. In both species, no significant difference of apparent digestibility coefficient of protein was observed between different carbohydrate sources. Dietary carbohydrate sources significantly affected body composition, and liver phosphoenolpyruvate carboxykinase (PEPCK), pyruvate kinase (PK), glucose 6‐phosphate dehydrogenase (G6PD) and malic enzyme (ME) activities also varied according to dietary carbohydrate complexity. Fish with different food habits showed different abilities to synthesize liver glycogen, and the liver glycogen content in gibel carp was significantly higher than in Chinese longsnout catfish. The influence of carbohydrate source on gluconeogenesis and lipogenesis was also different in the two fish species.     

Carbohydrate molecule size affects the metabolic and digestive dynamics of jundiá (Rhamdia quelen)

This experiment was conducted to study the effects of carbohydrates with different molecular sizes on growth performance, feed utilization and composition, activity of digestive enzymes, plasma and hepatic metabolites of jundiá (Rhamdia quelen). Triplicate groups of jundiá (4.08 ± 0.005 g) were stocked in 12 tanks with stocking density of 25 individuals per tank and fed for 40 days with four isonitrogenous diets (37%) and isocaloric diets (3,200 kcal/kg) containing fructose (FRU), sucrose (SUC), maltodextrin (MALDEX) or corn starch (CS). The results showed no significant differences for growth variables and digestive enzymes. Fish whose diet received maltodextrin showed higher levels of deposited body fat and hepatosomatic index. Moreover, the above‐mentioned treatment resulted in lower concentrations of glucose and cholesterol in the plasma of jundiá, higher levels of triglycerides, and lower reserves of glucose and liver glycogen. However, fish fed the starch‐based diet presented higher moisture content, crude protein deposition, and body protein retention coefficient. In that same treatment, the jundiá presented higher levels of plasma glucose and liver protein. In conclusion, the efficiency of using digestible carbohydrates in iso‐nutritional diets for jundiá depends on the size of their molecular structure. The corn starch was the best dietary carbohydrate source for jundiá, based on feed utilization and composition and greater synchronicity between energy utilization and protein synthesis.     

Effects of dietary vitamin C on growth,flesh quality and antioxidant capacity of juvenile golden pompano Trachinotus ovatus

To investigate the effects of dietary vitamin C on growth, flesh quality and antioxidant capacity of juvenile golden pompano Trachinotus ovatus, a 56‐day feeding trial with five graded levels of dietary VC (D1: 11.69, D2: 34.89, D3: 59.10, D4: 114.26 and D5: 227.93 mg VC per kg of diet) was performed on 375 fish (triplicate groups of 25 fish per diet, initial weight 13.57 ± 0.09 g). Results showed that fish of D3 group exhibited the maximum specific growth rate (SGR) and the highest liver enzymatic activities of catalase (CAT) and glutathione peroxidase (GSH‐PX), which were consistent with the expression levels of cat and gsh‐px. Besides, the D3 group also showed higher contents of protein and lipid, and lower cooking loss, drip loss and malondialdehyde content in muscle than D1 group. The docosahexaenoic acid proportion in muscle increased with increasing dietary VC levels. Furthermore, the lowest expression levels of carnitine palmitoyltransferase1 (cpt1) and peroxisome proliferator‐activated receptor α (pparα) were detected in livers of D3 group. The optimum dietary VC level was 49.73 mg/kg from the broken‐line analysis based on the SGR, in which better growth performance, antioxidative ability and flesh quality were observed in T. ovatus juveniles.     

Effect of weaning time on the performance of Trachinotus ovatus (Linnaeus 1758) larvae

Effect of weaning time on the larval performance of golden pompano Trachinotus ovatus was studied in the experimental condition. The same weaning regime started on four different days of posthatch (DPH): 13 DPH (W13), 16 DPH (W16), 19 DPH (W19) and 22 DPH (W22), respectively. Growth, survival, RNA/DNA ratios and mid‐gut cell height of fish were assessed in each weaning regime over time. Growth and survival rates of fish larvae weaned in the W19 and W22 regimes were significantly higher than those in the W13 and W16 regimes. No significant differences were found either between W19 and W22, or between W13 and W16 treatments. Fish showed a decrease in the RNA/DNA ratio in W13, but a trend of increase in W16, W19 and W22. Weaning time significantly affected the mid‐gut cell height in larval golden pompano. On 24 DPH, the mid‐gut cell height of fish in the W13 and W16 treatments was significantly thinner than those in the W19 and W22 treatments. Based on fish growth, survival, RNA/DNA ratio and mid‐gut cell height, weaning can be started on 13 DPH in golden pompano larvae, but we recommend that the best weaning window be 16–22 DPH. These results are supported by histological and nutritional evidence and would guide the weaning process for golden pompano larvae, and offer a useful approach to explore the weaning protocol in larval fish rearing.     

Effect of salinity on the rearing performance of juvenile golden pompano Trachinotus ovatus (Linnaeus 1758)

Effect of rearing salinity on the performance of juvenile golden pompano Trachinotus ovatus (Linnaeus 1758) was studied under a laboratory condition. Fish growth, survival, RNA/DNA ratio, pepsin activity, α‐amylase activity and FCR were used as evaluation criteria. The growth and RNA/DNA ratio were significantly affected by the rearing salinity. High growth rate and RNA/DNA ratio were observed when fish were reared at the salinity of 34‰. The pepsin activity of fish was not significantly affected by the rearing salinity. However, the α‐amylase activity of fish was significantly affected by the rearing salinity. The α‐amylase activity of fish reared at the salinity of 10‰ was significantly lower than fish cultured at the salinity of 34‰. Rearing salinity can significantly affect the FCR of juvenile golden pompano. The FCR of fish cultured at the salinity of 10‰ was 5‐times higher than the FCR of fish reared at 34‰. Results from the present study indicate that juvenile golden pompano can be reared above 26‰ without affecting fish performance, and the salinity of 10‰ may be too low to rear juvenile golden pompano as fish growth, RNA/DNA ratio and α‐amylase activity were reduced.     

Molecular adaptations of glucose and lipid metabolism to different levels of dietary carbohydrates in juvenile Japanese flounder Paralichthys olivaceus

Japanese flounder juveniles (initial body weight: 7.12 ± 0.02 g) were fed three diets containing 0, 120 and 200 g/kg of carbohydrates (C0, C120 and C200, respectively) for 10 weeks. Results showed that higher dietary carbohydrate intake enabled further deposition of glycogen and lipids in liver and muscle. The mRNA levels of glucokinase (gck), phosphofructokinase (pfkl) and hexokinase (HK) activity involved in glycolysis were significantly up‐regulated in C120 (p < .05) but showed no further up‐regulation except for gck in C200. Besides, the gluconeogenic phosphoenolpyruvate carboxykinase 1 (pck1) mRNA levels were down‐regulated significantly in fish fed the C120 (p < .05). However, further increase in dietary carbohydrate levels increased the mRNA levels and activities of enzymes involved in gluconeogenesis and lipolysis (p < .05). Additionally, plasma glucose remained unchanged in C120 (p > .05) but significantly increased in C200 group (p < .05). In conclusion, Japanese flounder was able to use carbohydrates efficiently through regulation of glucose and lipid metabolism when dietary carbohydrate was not higher than 120 g/kg, while 200 g/kg of dietary carbohydrate caused the deregulation of glucose homoeostasis.     

Effect of different sources and forms of dietary carbohydrates on growth performance,body indices and lipogenesis activity of striped catfish Pangasianodon hypophthalmus fingerlings

A 12‐week feeding trial was conducted to determine a suitable carbohydrate source and form for Pangasianodon hypophthalmus. Ten isoenergetic, isonitrogenous and isolipidic diets, including five carbohydrate sources (dextrin, potato starch, wheat starch, corn starch and sago starch) and two carbohydrate forms (raw and cooked), were formulated. Results showed that specific growth rate, weight gain percentage, whole‐body lipid and 6‐phosphogluconate dehydrogenase enzyme activity of fish fed with cooked carbohydrates were significantly lower (p < .05) than those fed with raw carbohydrates (p < .05). Similarly, the fatty acid synthase enzyme activity of fish fed with the cooked form of carbohydrates was significantly lower (p < .05) than that fed with the raw form of carbohydrates except fish fed with cooked potato starch. The blood glucose level and malic enzyme activity of fish fed with cooked carbohydrate were significantly (p < .05) higher than those fed with raw carbohydrate. In summary, this study showed that cooked starch is an unsuitable dietary carbohydrate form for Pangasianodon hypophthalmus fingerlings. The raw forms of dextrin starch and potato are suitable dietary carbohydrate sources for further scientific studies on the carbohydrate utilization of P. hypophthalmus.     

Effects of protein and carbohydrate levels on survival,consumption and gonad index in adult sea urchin Strongylocentrotus purpuratus (Stimpson 1857) from Baja California,Mexico

A greater understanding of dietary protein and carbohydrate levels with regard to gonad production in Strongylocentrotus purpuratus would increase our nutritional knowledge of this sea urchin and guide the development of formulated diets for such aquaculture target species. A total of 255 purple sea urchins were captured from Ensenada Bay, Mexico, and maintained in 200‐L tanks for 9 weeks. Formulated diets that contained 30%, 26%, 23%, 20% and 17% of protein and 42%, 46%, 50%, 54% and 58% carbohydrates were offered ad libitum. Survival was affected by diets; urchins that were fed high‐protein–low‐carbohydrate diet experienced decreased survival. No significant differences were found in gonad index, but gonad production efficiency was lower in urchins that were fed a medium‐low‐protein–medium‐high‐carbohydrate diet. Urchins that were fed high carbohydrate levels utilized protein more efficiently and showed better digestibility of the diet and protein. These data suggest that all of our diets support gonad growth, but in terms of consumption, a diet that contains protein levels of 17% and 23% with carbohydrate levels of 50% and 58% are beneficial for S. purpuratus.     

Effects of replacement of fishmeal with cottonseed protein concentrate on the growth,intestinal microflora,haematological and antioxidant indices of juvenile golden pompano (Trachinotus ovatus)

A 56‐day feeding trial was conducted to investigate the effects of replacing fish meal with cottonseed protein concentrate (CPC) (free gossypol < 7.9 mg/kg) in the diets on the growth, intestinal microflora, haematological and antioxidant indices of juvenile golden pompano (Trachinotus ovatus). Six diets were designed: fishmeal diets (FM) which contained 340 g/kg fishmeal, as well as five CPC diets, each with differing CPC concentrations (120, 240, 360, 480 and 600 g/kg) to replace the fish meal. The weight gain rate (WGR) and specific growth rate (SGR) showed no significant difference among groups (p > .05) with the dietary CPC level ranged from 0 to 360 g/kg. Serum cholesterol (CHO) of C36 and triglyceride (TG) levels of C36 and C12 were significantly higher than the FM (p < .05). Total protein (TP) levels of C12 were significantly lower than the FM (p < .05). Among the treatments, C36 had higher glutathione peroxidase (GSH‐PX) and total superoxide dismutase (T‐SOD) than FM (p < .05). From the data analysis of 16s sequencing, with increasing CPC concentration, the proportion of harmful microbial taxa (Proteobacteria and Vibrio) increased. The results of this study support that CPC products are acceptable in practical diets for golden pompano. And the optimal dietary CPC replacement of golden pompano was estimated to be 259.3 g/kg.     

Nutritional regulation of hepatic glucose metabolism in fish

Glucose plays a key role as energy source in the majority of mammals, but its importance in fish appears limited. Until now, the physiological basis for such apparent glucose intolerance in fish has not been fully understood. A distinct regulation of hepatic glucose utilization (glycolysis) and production (gluconeogenesis) may be advanced to explain the relative inability of fish to efficiently utilize dietary glucose. We summarize here information regarding the nutritional regulation of key enzymes involved in glycolysis (hexokinases, 6-phosphofructo-1-kinase and pyruvate kinase) and gluconeogenesis (phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase) pathways as well as that of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. The effect of dietary carbohydrate level and source on the activities and gene expression of the mentioned key enzymes is also discussed. Overall, data strongly suggest that the liver of most fish species is apparently capable of regulating glucose storage. The persistent high level of endogenous glucose production independent of carbohydrate intake level may lead to a putative competition between exogenous (dietary) glucose and endogenous glucose as the source of energy, which may explain the poor dietary carbohydrate utilization in fish.     

Effects of dietary glucose and starch levels on the growth,haematological indices and hepatic hexokinase and glucokinase mRNA expression of juvenile mirror carp (Cyprinus carpio)

The effect of the different dietary carbohydrate types and levels on growth performance, haematological indices and hepatic hexokinase (HK) and glucokinase (GK) genes expression involved in control of glucose metabolism, was studied in juvenile mirror carp (Cyprinus carpio). Two carbohydrates (glucose and starch) diets with two levels (250 and 500 g kg^?1) were fed to triplicate groups of 35 fish for 60 days. The best weight gain rate and specific growth rate were observed in fish fed with 250 g kg^?1 glucose diet and 500 g kg^?1 starch diet (P < 0.05). Fish fed with 500 g kg^?1 glucose showed low feed utilization, with the highest food conversion ratio and the lowest protein efficiency ratio (P < 0.05). Hepatosomatic index was significantly higher in fish fed with glucose diets and the 500 g kg^?1 starch diet compared to 250 g kg^?1 starch. CHOL, HDL‐C and LDL‐C were significantly highest in fish fed with 500 g kg^?1 starch than all other diets (P < 0.05). Hepatic GK mRNA expression level and activity were positively related to glucose and starch levels (P < 0.05). Correlation analysis showed that hepatic glycogen concentration was increased by dietary carbohydrate content (P < 0.05). These results suggest that GK may play a major role in the postprandial glucose utilization in juvenile mirror carp.     

Replacement of Dietary Fish Meal with Poultry By‐product Meal and Soybean Meal for Golden Pompano,Trachinotus ovatus,Reared in Net Pens

Two 8‐wk feeding trials were conducted to examine the effect of replacing dietary fish meal with poultry by‐product meal (PBM) and soybean meal (SBM) on growth, feed utilization, body composition, and wastes output of juvenile golden pompano, Trachinotus ovatus (initial body weight 16.7 g), reared in net pens. A control diet (C) was formulated to contain 35% fish meal. In Trial I, dietary fish meal level was reduced to 21, 14, 7, and 0% by replacing 40, 60, 80, and 100% of the fish meal in diet C with PBM. The weight gain (WG), nitrogen retention efficiency (NRE), and energy retention efficiency (ERE) decreased, while the feed conversion ratio (FCR) and total waste output of nitrogen (TNW) increased, with the fish meal level reducing from 35 to 21%. No significant differences were found in the hepatosomatic index, viscersomatic index, and body composition between fish fed diet C and test diets. In Trial II, a 2 × 2 layout was established, and 40 and 60% of the fish meal in diet C was replaced by either PBM or SBM. At the same fish meal replacement level, the WG and NRE were higher and the FCR and TNW were lower in fish fed the diets with fish meal replaced by PBM than in fish fed the diets with fish meal replaced by SBM. The results of this study indicate that more than 21% fish meal must be retained in diets for golden pompano when PBM or SBM is used alone as a fish meal substitute.