Dietary Carbohydrate Levels Research Articles

The effects of dietary carbohydrate on the growth, antioxidant capacities, innate immune responses and pathogen resistance of juvenile Black carp Mylopharyngodon piceus.

The present study was focused on the growth, antioxidant capacities, innate immune responses and pathogen resistance in juvenile Black carp Mylopharyngodon piceus fed with graded levels of dietary carbohydrate (CHO) (0.6, 106.5, 194.3, 288.4, 379.1 and 473.8gkg(-1)) for 9 weeks. Results showed that highest weight gain and special growth ratio was obtained at 288.4gkg(-1) dietary CHO. And adequate dietary CHO content (288.4gkg(-1)) could significantly increase the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (Gpx), promote reduced glutathione (GSH) content and then increase the total antioxidant capacities (TAOC) in the liver of M.piceus. However, the malondialdehyde (MDA) levels in the fish liver could be significantly aggravated by excessive dietary CHO. Serum cortisol (COL) levels could be significantly increased in juvenile Black carp M.piceus fed with 379.1gkg(-1) dietary CHO compared with CHO-deficient diets. Activities of alanine transaminase (GPT) and aspartate transaminase (GOT) were both decreased in the serum of juvenile Black carp M.piceus fed with 194.3gkg(-1) dietary CHO compared with CHO-deficient diets (0.6 and 106.5gkg(-1)) or CHO-excess diets (379.1 and 473.8gkg(-1)). In addition, 288.4gkg(-1) dietary CHO could significantly up-regulate the mRNA expression levels of hepcidin (HEPC), natural resistance-associated macrophage protein (NRAMP), tumor necrosis factor-α (TNF-α) and interferon (IFN), lysozyme (LYZ) and complement component 3 (C3) in the blood and liver samples of juvenile Black carp M.piceus compared with the CHO-deficient diets (0.6 and 106.5gkg(-1)). Moreover, 288.4gkg(-1) dietary CHO could also enhance the contents of C3 and plasma nitrogen monoxide (NO), and increase the activities of LYZ and total nitric oxide synthase (t-NOS) in the serum compared with the CHO-deficient or CHO-excess diets. Furthermore, the survival rates were also increased by adequate dietary CHO (194.3 and 288.4gkg(-1)) fed to juvenile Black carp M.piceus after infection with Aeromonas hydrophila. In conclusion, these results suggest that adequate dietary CHO (288.4gkg(-1)) could increase growth, reduce oxidative stress, enhance innate immune responses, improve the health states and then promote disease resistance in juvenile Black carp M.piceus.

Effects of Dietary Carbohydrate on Weight Gain and Gonad Production in Small Sea Urchins, Lytechinus variegatus.

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi-purified formulated diets (n = 16 individuals treatment-1). In the diets, protein was held constant (310g kg-1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg-1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48g wet weight, n= 40) fed 190 g kg-1 carbohydrate consumed significantly more dry feed than those fed 260 g kg-1, but not more than those fed 380 g kg-1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg-1 body weight day-1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.

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 Ri

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.

Omega-3 and -6 fatty acids allocate somatic and germline lipids to ensure fitness during nutrient and oxidative stress in Caenorhabditis elegans

Animals in nature are continually challenged by periods of feast and famine as resources inevitably fluctuate, and must allocate somatic reserves for reproduction to abate evolutionary pressures. We identify an age-dependent lipid homeostasis pathway in Caenorhabditis elegans that regulates the mobilization of lipids from the soma to the germline, which supports fecundity but at the cost of survival in nutrient-poor and oxidative stress environments. This trade-off is responsive to the levels of dietary carbohydrates and organismal oleic acid and is coupled to activation of the cytoprotective transcription factor SKN-1 in both laboratory-derived and natural isolates of C. elegans. The homeostatic balance of lipid stores between the somatic and germ cells is mediated by arachidonic acid (omega-6) and eicosapentaenoic acid (omega-3) precursors of eicosanoid signaling molecules. Our results describe a mechanism for resource reallocation within intact animals that influences reproductive fitness at the cost of somatic resilience.

Balancing macronutrient intake in cultured Lytechinus variegatus

Among aquatic organisms, nutritional requirements are historically assessed by evaluating formulated diets with changes in a single nutrient profile. These studies provide organisms with the option of regulating the total feed intake but do not enable individuals to regulate intake of specific nutrient ratios. An alternate experimental approach, known as the geometric framework (GF) for nutrition, tests whether organisms held under specific conditions have optimal target intake levels for particular nutrients and whether, when provided with diet choices, they will self-regulate nutrient intake to reach these specific targets. In this study, we used the GF to assess intake levels of dietary protein and carbohydrate in cultured adults of the sea urchin Lytechinus variegatus provided choices between diets varying in both dry matter and specific macronutrient concentrations. Adult urchins (ca. 120g) held previously on formulated diets were offered moist gel-based diets in pairwise combinations. Diets varied in levels of fish meal isolate (as a protein source) and wheat starch (as a carbohydrate source) and in nutrient concentration (5 or 10% dry matter). Regardless of diet combination, individuals maintained an average dietary protein intake of ca. 0.047–0.061gday−1. Dietary carbohydrate intake was not regulated to a specific level and ranged from 0.042–.0136gday−1. These data suggest that large adult L. variegatus held in culture have a tightly regulated intake target for dietary protein but not carbohydrate. Regardless of nutrient ratios or macronutrient concentration, individuals adjusted intake patterns to defend this target. We suggest that the GF will be an important tool in evaluating macronutrient requirements in cultured sea urchins and other aquatic species.

Effects of dietary carbohydrate level on growth, biochemical composition and glucose metabolism of juvenile sea cucumber Apostichopus japonicus (Selenka)

A 60-day feeding experiment was conducted to evaluate the effects of dietary carbohydrate level on growth performance, feed utilization, biochemical composition and glucose metabolism of juvenile sea cucumber. The sea cucumbers were fed five isonitrogenous and isolipidic diets containing graded levels of carbohydrate from 25.61% to 66.09%, to investigate the optimum dietary carbohydrate level. The results revealed that specific growth rate (SGR) and feed conversion efficiency (FCE) first significantly increased then declined as dietary carbohydrate level increased. The relatively higher protein efficiency ratios (PER) in diets with carbohydrate levels of 45.31% and 55.82% implied that carbohydrate supplied energy to gain the protein sparing effect. Apparent digestibility coefficients (ADC) of dry matter, crude protein, carbohydrate and gross energy were all significantly affected by dietary carbohydrate level. The high dietary carbohydrate level resulted in the increased glycogen biosyntheses and lipid deposition, accelerated glycolysis and decelerated gluconeogenesis to maintain glucose homoeostasis. Glycolytic enzyme activities of hexokinase (HK), pyruvate kinase (PK) and lactate dehydrogenase (LDH), and succinate dehydrogenase (SDH) showed an ascending trend as dietary carbohydrate level increased at the initial stage. However, PK, LDH, lipogenic enzyme activity of glucose-6-phosphate dehydrogenase (G-6-PD), gluconeogenic enzyme activity of fructose-1,6-bisphosphatase (FDPase), amylase activity and cortisol level significantly decreased at the highest dietary carbohydrate level of 66.09%, and glucose in coelomic fluid significantly increased, which demonstrated that excess dietary carbohydrate might lead to the inhibition of glucose metabolism. Based on the second-order polynomial regression models of SGR and FCE, it was concluded that 48.56%–49.30% dietary carbohydrate levels were optimal for Apostichopus japonicus.

Dietary carbohydrate and food processing affect the digestive physiology ofPiaractus mesopotamicus

The responses of the digestive physiology of juvenile pacu to different diet processing were studied. Fish were fed with isoproteic diets with 260 g kg−1 of crude protein (CP) containing different levels of carbohydrate (DCh) (400 or 500 g kg−1), and two diet processing (pelletization or extrusion) for 90 days. Fish fed with extruded diets showed decrease of the gastrointestinal transit time (GI transfer) and of the amylase activity, but maltase activity did not alter. Protease activity of intestine depicted increase when the DCh was raised. The increase of DCh also caused enhancement of the apparent digestibility coefficient of CP (ADCCP) in fish fed with extruded diets. Fish fed with pelletized diets showed increase of the amylase activity in pyloric caecum independently of the dietary carbohydrate level. No interaction was observed between dietary carbohydrate level and diet processing. Maltase activities from the stomach and intestine of pacu were not responsive to the carbohydrate level. The extrusion process improved the carbohydrate availability and the digestion efficiency of protein in pacu. Digestive enzymes of pacu were modulated either by nutrients or diet processing.

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.

Nutritional and metabolic responses in common dentex (Dentex dentex) fed on different types and levels of carbohydrates

The present study was aimed to evaluate the capacity of common dentex (Dentex dentex) to efficiently use dietary carbohydrates. So, the effects of different type and levels of carbohydrates on growth performance, feed utilization, fish composition, plasma metabolites and key metabolic pathways in liver and white muscle of common dentex are presented. Nine isonitrogenous (43%) and isoenergetic (22MJkg−1) diets were formulated combining three types, pregelatinized starch (PS), dextrin (Dx) and maltodextrin (Mx), and three levels (12, 18 and 24%) of carbohydrates. Growth performance was not significantly influenced by treatments. The best feed utilization was observed in 18% Mx group. Higher hepatic lipid content was found in fish fed lower dietary carbohydrate levels. PS induced higher liver and white muscle hexokinase and pyruvate kinase activities compared to the lower values observed for Mx. Malic enzyme and glucose 6-phosphate dehydrogenase in liver and white muscle were lower in Mx group. The influence of dietary carbohydrates source was more noticeable than those induced by the carbohydrate level, when glycolysis and lipogenesis pathways were considered. Common dentex is able to use properly dietary carbohydrates, although optimal dietary inclusion levels are below 24%. The greater protein-sparing effect was promoted by the less complex carbohydrate (maltodextrin) and the best feed utilization indices were obtained at intermediate levels of inclusion (18%).

Effect of dietary carbohydrate levels on growth performance, body composition, intestinal and hepatic enzyme activities, and growth hormone gene expression of juvenile golden pompano, Trachinotus ovatus

Abstract A growth trial was conducted to determine the optimum dietary carbohydrate level of juvenile golden pompano ( Trachinotus ovatus ). Six isonitrogenous and isoenergetic experimental diets (43% crude protein and 16.8 MJ kg − 1 diet) using corn starch as the carbohydrate source were formulated to contain six carbohydrate levels. Each diet was tested in triplicate for 8 weeks. Weight gain, specific growth rate, feed intake, protein efficiency ratio, hepatosomatic index, and viserosomatic index increased significantly as dietary starch levels increased from 0% to 16.8% ( P P P > 0.05) among all treatments. Carcass lipid content decreased but carcass protein content increased significantly as dietary carbohydrate levels increased ( P P > 0.05) among all treatments. Glycogen content in muscle and liver increased significantly as dietary carbohydrate levels increased ( P P + , K + -ATPase activities all increased with dietary carbohydrate levels up to 11.2% ( P P > 0.05). Hepatic hexokinase activity increased and hepatic glucose-6-phosphatase activity decreased significantly as dietary carbohydrate levels increased ( P P > 0.05). Expression of hepatic growth hormone (GH) gene was positively related to growth performance. In conclusion, results suggested that the optimum carbohydrate level for juvenile golden pompano could be 11.2–16.8% of the diet.

Fasted and postprandial response of serum physiological response, hepatic antioxidant abilities and HSP70 expression in Wuchang bream (Megalobrama amblycephala) fed different dietary carbohydrate levels

The effect of dietary carbohydrate (CHO) level on serum physiological response, hepatic antioxidant abilities and heat shock protein 70 (HSP70) expression of Wuchang bream (Megalobrama amblycephala) was studied. Two isonitrogenous (28.56% crude protein) and isolipidic (5.28% crude lipid) diets were formulated to contain 30% or 53% wheat starch. Diets were fed for 90 days to fish in triplicate tanks (28 fish per tank). At the end of feeding trial, significantly higher serum triglyceride level, insulin level, cortisol level, and malondialdehyde (MDA) content were observed in fish fed the 53% CHO diet, while significantly lower serum total protein content, alkaline phosphatase activity, superoxide dismutase activity and total antioxidative capacity were found in fish fed the 53% CHO diet compared with those fed the 30% diet. The relative level of hepatic heat shock protein 70 mRNA was significantly higher in the 53% CHO group than that in the 30% CHO at 6, 12 and 48 h after feeding. Ingestion of 53% dietary CHO impacts the nonspecific immune ability and causes metabolic stress in Megalobrama amblycephala.

Gastrointestinal transit of extruded or pelletized diets in pacu fed distinct inclusion levels of lipid and carbohydrate

The objective of this work was to evaluate the effect of pelletized or extruded diets, with different levels of carbohydrate and lipid, on the gastrointestinal transit time (GITT) and its modulation in pacu (Piaractus mesopotamicus). One hundred and eighty pacu juveniles were fed with eight isonitrogenous diets containing two carbohydrate levels (40 and 50%) and two lipid levels (4 and 8%). Four diets were pelletized and four were extruded. Carbohydrate and lipid experimental levels caused no changes to the bolus transit time. However, the bolus permanence time was related to diet processing. Fish fed pelletized diets exhibited the highest gastrointestinal transit time. Regression analysis of bolus behavior for pelletized and extruded diets with 4% lipid depicted different fits. GITT regression analysis of fish fed 8% lipid was fitted to a cubic equation and displayed adjustments of food permanence, with enhanced utilization of the diets, either with extruded or pelletized diets. GITT of fish fed extruded diets with 4% lipid was adjusted to a linear equation. The GITT of pacu depends on the diet processing and is affected by dietary levels of lipid and carbohydrate.

Growth, Body Composition, and Ammonia Tolerance of Juvenile White ShrimpLitopenaeus vannameiFed Diets Containing Different Carbohydrate Levels at Low Salinity

Effects of dietary carbohydrate (CBH) levels on growth, body composition, and ammonia tolerance of juvenile white shrimp Litopenaeus vannamei at a low salinity of three were evaluated. Six isonitrogenous and isolipid diets containing different CBH levels were formulated and fed to juvenile L. vannamei for 42 days in triplicate for each treatment. Weight gain and survival rate of shrimp fed 20% CBH were the greatest and differed from those fed 5% CBH and 30% CBH. Shrimp whole-body crude protein of the 20% CBH group was significantly greater than that of other treatments. Whole-body crude lipid levels increased with the increase of dietary CBH, and was significantly higher in the 20%, 25%, and 30% CBH groups than in the control. Hepatosomatic index, condition factor, whole-body moisture, and ash contents were not affected by dietary CBH levels. Hepatopancreas soluble protein peaked in shrimp fed 20% CBH, and was significantly greater than in other groups. Hepatopancreas and muscle glycogen showed a similar tendency, but peaked in shrimp fed 15% CBH. Malate dehydrogenase, pyruvate kinase, and glucose-6-phosphate dehydrogenase activities were not affected significantly by dietary CBH levels. An ammonia challenge of 96 h showed that the shrimp in the 20% CBH group had the greatest survival rate, although no significant differences were observed among treatments. This study indicates that 15%–20% dietary CBH is optimal for growth and can improve the ability of L. vannamei to handle stress at low salinities.

Growth, Body Composition, and Ammonia Tolerance of Juvenile White ShrimpLitopenaeus vannameiFed Diets Containing Different Carbohydrate Levels at Low Salinity

Effects of dietary carbohydrate (CBH) levels on growth, body composition, and ammonia tolerance of juvenile white shrimp Litopenaeus vannamei at a low salinity of three were evaluated. Six isonitrogenous and isolipid diets containing different CBH levels were formulated and fed to juvenile L. vannamei for 42 days in triplicate for each treatment. Weight gain and survival rate of shrimp fed 20% CBH were the greatest and differed from those fed 5% CBH and 30% CBH. Shrimp whole-body crude protein of the 20% CBH group was significantly greater than that of other treatments. Whole-body crude lipid levels increased with the increase of dietary CBH, and was significantly higher in the 20%, 25%, and 30% CBH groups than in the control. Hepatosomatic index, condition factor, whole-body moisture, and ash contents were not affected by dietary CBH levels. Hepatopancreas soluble protein peaked in shrimp fed 20% CBH, and was significantly greater than in other groups. Hepatopancreas and muscle glycogen showed a similar tendency, but peaked in shrimp fed 15% CBH. Malate dehydrogenase, pyruvate kinase, and glucose-6-phosphate dehydrogenase activities were not affected significantly by dietary CBH levels. An ammonia challenge of 96 h showed that the shrimp in the 20% CBH group had the greatest survival rate, although no significant differences were observed among treatments. This study indicates that 15%–20% dietary CBH is optimal for growth and can improve the ability of L. vannamei to handle stress at low salinities.

Effect of dietary carbohydrate on non-specific immune response, hepatic antioxidative abilities and disease resistance of juvenile golden pompano (Trachinotus ovatus)

The present study was conducted to investigate the effects of dietary carbohydrate (CHO) levels on non-specific immune responses, hepatic antioxidative status and disease resistance of juvenile golden pompano. Fish were fed six isonitrogenous and isoenergetic diets containing various CHO levels for 8 weeks. After the feeding trial, fish were challenged by Vibrio harveyi and survival rate was recorded for the next 12 days. Plasma total protein and albumin content, respiratory burst activity, alkaline phosphatase, slightly increased with dietary starch level from 0% to 16.8%, but significantly decreased at dietary starch levels of 16.8%–28%. Plasma lysozyme, complement 3 and complement 4 levels increased with increasing dietary carbohydrate up to 11.2% and then declined (P < 0.05). Contrary to glutamic-oxalacetic transaminase and triiodothyronine, plasma cortisol content increased with increasing dietary carbohydrate up to 22.4%, and then levelled off. The hepatic total antioxidative capacity, reduced glutathione and catalase levels reached the peak at the fish fed diet with 16.8% carbohydrate (P < 0.05). This also held true for hepatic superoxide dismutase activities, whereas the hepatic malondialdehyde content of fish fed dietary starch level of 16.8% was significantly lower than that of fish fed no CHO diet, but showed little difference (P > 0.05) with those of the other treatments. After challenge, fish fed 11.2% and 16.8% dietary CHO showed higher survival rate than that of fish in 0% CHO group (P < 0.05). However, survival rate showed little difference among 0%, 5.6%, 22.4% and 28% CHO groups (P > 0.05). The results of this study suggest that ingestion of 11.2–16.8% dietary CHO can enhance the non-specific immune responses, increase the hepatic antioxidant abilities, and improve resistance to V. harveyi infection of juvenile golden pompano.

Growth performance and thyroid hormones of Caspian kutum, Rutilus frissi, juveniles in response to dietary carbohydrate levels

The aim of this study was to evaluate the effects of a practical diet containing different carbohydrate levels on growth rate, feed utilization, and thyroid hormones (T3 and T4) of Caspian kutum fingerlings. Fish with an initial average weight of 0.8 ± 0.2 g were fed five formulated isonitrogenous and isoenergetic diets with different carbohydrate levels of 15, 20, 25, 30 and 35 % in triplicate groups for 10 weeks. Based on the results, growth performance of Rutilus frissi was significantly affected by the dietary carbohydrate levels (P 0.05). The highest amount of T4 was observed in kutum juveniles fed with a carbohydrate level of 15 %. The levels of T4 were significantly affected by dietary carbohydrate levels (P < 0.05) with the highest amount in kutum juveniles fed 15 % of carbohydrate. In conclusion, this study indicates that increasing carbohydrate levels from 15 to 35 %, with no negative effects on growth parameters in R. frissi juveniles, leads to an efficient protein ratio and optimal growth. Moreover, no clear correlation was found between fish growth and thyroid hormones.

Nutritional regulation of glucokinase: a cross-species story.

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

Adipose tissue and liver metabolic responses to different levels of dietary carbohydrates in gilthead sea bream (Sparus aurata)

This study analyzes the effects of replacing dietary lipids by carbohydrates and carbohydrates by fiber on gilthead sea bream growth, as well as lipid and glucose metabolism in adipose tissue and liver over the course of a 15-week feeding trial. Six different diets were formulated and fish were classified into two experimental groups sharing one diet. In the first group (LS), fish were fed four diets where lipids were reduced (23%–17%) by increasing carbohydrates (12%–28%) and, the second group (SF) consisted on three diets where the amount of carbohydrates (28%–11%) was exchanged at expenses of fiber (1%–18%). Differences in growth were not observed; nevertheless, the hepatosomatic index was positively related to dietary starch levels, apparently not due to enhanced hepatic lipogenesis, partly supported by unchanged G6PDH expression. In the LS group, lipogenic activity of adipose tissue was stimulated with low-lipid/high-carbohydrate diets by up-regulating G6PDH expression and a tendency to increase FAS, and promoted carbohydrate utilization versus fatty acid oxidation by modulating the transcription factors LXRα, PPARα and PPARβ expression. In the SF group, PPARs and LXRα increased parallel to fiber levels in adipose tissue. Furthermore, an adaptation of hepatic GK to dietary starch inclusion was observed in both groups; however, the lack of effects on G6Pase expression indicated that gluconeogenesis was not nutritionally regulated under the conditions examined. Overall, metabolic adaptations directed to an efficient use of dietary carbohydrates are present in gilthead sea bream, supporting the possibility of increasing carbohydrate or fiber content in diets for aquaculture sustainability.

Effect of temperature and varying level of carbohydrate and lipid on growth, feed efficiency and nutrient digestibility of brook trout, Salvelinus fontinalis (Mitchill, 1814)

Temperature is the most important environmental factor determining the growth rate of fish. Increasing summer temperatures in salmonid growing regions worldwide are presenting new challenges for effective nutrient delivery, particularly as feeds increasingly replace fish oil with cheaper and available energy sources. The effect of temperature and non-protein energy sources on growth performance, nutrient utilisation and digestibility of brook trout, Salvelinus fontinalis was evaluated at temperatures reflective of optimum, 15°C, and elevated summer conditions, 19°C. The experiment was a 2×4 factorial design with two temperatures (15°C and 19°C) and four iso-nitrogenous (protein: 440g/kg) and iso-energetic (22MJ/kg) diets. Diets were formulated with increasing carbohydrate level (180–260g/kg) balanced by decreasing lipid level (170–130g/kg). A 12-week study was conducted using triplicate group of brook trout with initial weight 48.0±3.46g at each temperature. Fish were fed 2% body weight ration daily. Growth rate was higher and feed utilisation was more efficient at 15°C than 19°C (P=0.00). Reduced fish oil inclusion and increased gelatinised carbohydrate had no effect on growth and feed utilisation at both temperatures. The apparent digestibility coefficients of nutrient and energy were significantly higher at 15°C than 19°C (P=0.00). Dry matter, gross energy and energy from carbohydrate were more digestible as dietary carbohydrate levels increased, at both temperatures. Increasing dietary carbohydrate generated an increase in the intestinal activity of α-amylase, which was higher at 15°C. Across the levels of dietary carbohydrate tested; there were no pathological changes to liver or intestine histology. Fish oil can be substituted with gelatinised carbohydrate under challenging high water temperatures in brook trout feeds, with no detriment to health, nutrient digestibility or growth performance.

Effects of dietary carbohydrate level on growth and body composition of juvenile giant croakerNibea japonica

An 8-week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition of giant croaker, Nibea japonica. The six diets were designated as carbohydrate level from 0% to 30%. Each diet was fed to triplicate groups of 18 giant croaker (initially weighing, 7.40 ± 0.15 g fish−1) in flow-through sea water system. The weight gain (WG) and special growth ratio (SGR) had tendency to increase with carbohydrate level from 0% to 12% after that decreased, and significantly lower in fish fed diet with 30% carbohydrate level than in other groups. Moreover, fish fed diet with 30% dietary carbohydrate has significantly higher feed conversion ratio (1.48 ± 0.18) and lower protein efficiency ratio (1.69 ± 0.21) than other groups (P < 0.05). The intraperitoneal fat ratio and condition factor had no significant difference in different groups (P > 0.05), hepatosomatic index value increased with dietary carbohydrate increased (P < 0.05). The result of this study also suggested that excess carbohydrate level (30%) led to lower lipid content in whole body. Based on the second-order polynomial regression analysis of WG and SGR, 12.2–12.7% dietary carbohydrate provided maximum growth of N. japonica.