Growth performance and metabolic utilization of diets including starch,dextrin, maltose or glucose as carbohydrate source by gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>) juveniles

The effect of dietary carbohydrate complexity on growth, feed utilization and activity of selected key liver enzymes of intermediary metabolism were studied in gilthead sea bream juveniles. Four isonitrogenous (50% crude protein) and isolipidic (16% crude lipids) diets were formulated to contain 20% of pregelatinized maize starch, dextrin, maltose or glucose. Triplicate groups of fish (117 g initial weight) were fed each diet to near satiation during 6 weeks. No effect of dietary carbohydrate on growth was noticed. Feed efficiency was lower in fish fed the glucose diet than the maltose and dextrin diets. The lowest protein efficiency ratio was observed in fish fed the glucose diet. Six hours after feeding, glycemia was higher in fish fed the glucose diet than the maltose and starch diets. Liver glycogen content was unaffected by dietary carbohydrate complexity. Hepatic glucokinase (GK) activity was higher in fish fed the glucose and the maltose diets, while higher pyruvate kinase (PK) activity was recorded in fish fed the glucose diet than in fish fed the starch diet. Fructose-1,6-bisphosphatase (FBPase) and glucose-6-phosphate dehydrogenase (G6PD) activities were higher in fish fed the starch diet compared to dextrin and glucose diets. Data suggest that dietary glucose and maltose are more effective than complex carbohydrates in enhancing liver glycolytic activity. Dietary glucose also seems to be more effective than starch in depressing liver gluconeogenic and lipogenic activities. Overall, dietary maltose, dextrin or starch was better utilized than glucose as energy source by gilthead sea bream juveniles.     

The use of locally produced fish meal and other dietary manipulations in practical diets for rainbow trout Oncorhynchus mykiss (Walbaum)

The aim of this trial was to compare the performance of rainbow trout fed diets including local or imported fish meal as the main protein sources, and to test the effect of reducing the fish meal content or including a fish protein hydrolysate in the diets. Two experimental diets were formulated to include 35% (diet 2) or 20% (diet 3) of a local processed whole fish meal; two other diets were formulated similar to diets 2 and 3 but with 5% fish protein hydrolysate replacing the same amount of fish meal (diets 4 and 5 respectively); a diet similar to diet 2, but including Norwegian fish meal, was used as a control (diet 1). The growth trial lasted 14 weeks and was carried out in floating net cages (325‐L capacity), with duplicate groups of 20 rainbow trout of an initial average weight of 58 g. The apparent digestibility coefficients (ADC) of the diets were evaluated in a separate laboratory trial. At the end of the growth trial, there were no significant differences in growth rate and protein efficiency ratio among groups. Feed conversion ratios were significantly better in groups fed diets 3, 4 and 5 than in the other groups. Nitrogen retention (% of N intake) was significantly higher in fish fed diets 4 and 5 than in those fed diet 2. There were no significant differences in energy retention (% of energy intake) among groups. At the end of the trial, there were no significant differences among groups in proximate composition of whole fish. The ADC of protein, energy and phosphorus of diets 1 and 2 were significantly lower than those of diets 3 and 5. It was concluded that, under the experimental conditions tested, performance of rainbow trout fed practical diets including good quality local processed fish meal is similar to that of fish fed diets including Norwegian fish meal. A reduction in the fish meal from 35% to 20% of the diet or the inclusion of a fish protein hydrolysate had no negative effects on growth performance and improved feed utilization.     

Recent advances in European sea bass and gilthead sea bream nutrition

European sea bass (Dicentrarchus labrax) and gilthead sea bream(Sparus aurata) are amongst the most important finfish speciescultured in the Mediterranean region. Production of these species isnowadays a well-controlled process, but knowledge of their nutritionalrequirements is still very limited. Nevertheless, a considerable amountof data has been accumulated in recent years, and the purpose of thispaper is to review the recent advances on the nutritional requirementsof sea bass and sea bream. The optimum protein to energy ratio of thediets of sea bass and sea bream seem to be higher than for salmonids,and there is some evidence that high dietary lipid levels have nobeneficial effects on fish performances. Although the essential aminoacid requirements were estimated by the ideal protein method, data basedon the dose-response method is only available for a few amino acids.Essential fatty acid requirements were estimated for sea bream juvenilesbut data is lacking for sea bass. Vitamin and mineral requirements ofthese species are practically unknown. Although the importance ofbroodstock nutrition on gonadal development, spawning and egg quality isrecognized, few studies were done to elucidate these aspects. The recentdevelopment of microparticulate diets for larvae will contribute to theaccurate evaluation of their nutritional requirements.     

Temperature and dietary carbohydrate level effects on performance and metabolic utilisation of diets in European sea bass (Dicentrarchus labrax) juveniles

This study aimed to evaluate the effect of temperature and dietary starch level on growth performance, nutrient utilisation, whole-body composition and activity of selected hepatic intermediary metabolism enzymes in European sea bass juveniles. An experimental diet was formulated to contain 46% crude protein, 12% crude lipids and 30% pregelatinized starch (diet 30GS); two other diets were formulated to include the same levels of all ingredients as diet 30GS except for the pregelatinized starch, which was included at 20% (diet 20GS) or 10% (diet 10GS). Diets were assigned to triplicate groups of 25 fish (initial weight: 15 g) at two water temperatures (18 and 25 °C) for 10 weeks. Group receiving diet 30GS was fed to apparent satiation and groups fed diets 20GS and 10GS were pair-fed according to group fed diet 30GS, so that each group ate the same amount of all nutrients except for carbohydrates. At the end of the trial, growth rate, feed efficiency and protein efficiency ratio were higher at 25 than at 18 °C. Dietary starch level did not affect growth or N utilisation. Feed efficiency was inversely related to dietary starch level. Whole-body lipids and energy content were higher at 25 °C and increased with dietary starch levels. Whole-body protein and ash content were also higher at 25 °C but were not affected by dietary starch level. Liver glycogen, HSI and VI increased with dietary starch level. ADC of starch was higher at 25 °C and within each temperature decreased with increasing dietary starch levels. ADC of protein was neither affected by temperature nor dietary starch levels. Data on enzyme activities showed that hexokinase (HK) but not glucokinase (GK) was affected by temperature. Dietary starch level affected the activities of glucokinase and glucose-6-phosphate dehydrogenase (G6PD) but not of the others enzymes tested (HK, PK, FBPase and GDH).     

Kaolin and seaweed-based extracts can be used as middle and long-term strategy to mitigate negative effects of climate change in physiological performance of hazelnut tree

Spraying plants with exogenous substances have gained more attention due to its potential to reduce the negative impacts of heat and water stress in a climate-changing environment. Therefore, the effects of spraying kaolin and Ascophyllum nodosum with and without irrigation on leaf gas exchange parameters, plant water status, electrolyte leakage, cuticular waxes, plant hormones and antioxidant enzymes, proline, malondialdehyde (MDA) content and lipid peroxidation of membranes of hazelnut trees were studied. Six different treatments with kaolin (K), A. nodosum (An), irrigation (I), kaolin with irrigation (Ki), A. nodosum with irrigation (Ani) and no irrigation (control) during two consecutive years (2016–2017) were applied in a hazelnut orchard of ‘Grada de Viseu’ cultivar located in Moimenta da Beira region, Northern Portugal. Results showed that K and An were effective for reducing hazelnut heat and drought stress by increasing the water relative content (RWC), net CO₂ assimilation (A), water use efficiency (A/g_s) and reducing the leaf mass per area (LMA), electrolyte leakage (EL). Moreover, concentration of ABA, MDA, proline and lipid peroxidation of membranes, as well the average content of antioxidant enzymes, was lower, suggesting that under K and An, plants have a better physiological performance than without these two exogenous substances. Nonetheless, these benefits only appear to be significant in the second year of the experiment showing that the use of both substances to mitigate climate change adverse effects should be considered as a long-term strategy.     

Correlations between disease severity,glucosinolate profiles and total phenolics and Xanthomonas campestris pv. campestris inoculation of different Brassicaceae

Many Brassicaceae species are economically important crops and Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot, is considered one of the most important necrotrophic plant bacterial diseases occurring worldwide on these and many other crops. Therefore identifying resistance mechanisms and genes is crucial. Researchers continue to investigate the role of phytochemicals (plant secondary metabolites) in protecting plants against diseases and pathogens. Glucosinolates (GLS), and more specifically their hydrolysis products, are known to have various biological effects including antimicrobial activity. From the positive results of initial in vitro studies with Xcc and other pathogenic bacteria new experiments were designed to evaluate the possible in planta role of GLS, and also phenolics, in the interaction with Xcc. The in planta studies, with various Brassicaceae seedlings, have shown a correlation between GLS profiles, and therefore the subsequent hydrolysis products, and the inhibition of Xcc growth. There were no significant correlations between Xcc infection and total phenolics. Positive correlations were found between specific and total GLS contents and the severity of disease. Further in vitro and in planta studies need to be performed to evaluate the role of GLS and other defense mechanisms in Xcc and other important bacterial infections of Brassicaceae crops.     

Isolation and detection of Fasciola hepatica DNA in Lymnaea viatrix from formalin-fixed and paraffin-embedded tissues through multiplex-PCR

Detection of Fasciola hepatica infection in Lymnaea viatrix through analysis of histological cuts is based upon morphological characters of the parasite during the intra-mollusk phase of parasitism. At this stage, trematode forms are very similar and, thus, very difficult to differentiate. Specific detection may also be impaired by the presence of other helminthes in the mollusk. Histological samples are usually fixed in formalin, embedded in paraffin, sectioned and HE stained. In the current study, a method for the extraction of DNA from formalin-fixed, paraffin-embedded tissues was standardized by means of deparaffinizing with xylol and digesting with proteinase K. Extracted DNA was amplified in a multiplex-PCR, by using simultaneous primers in a single reaction under high stringency conditions. Results showed specific amplification of DNA from the trematode and the snails. The technique was sensitive enough to detect F. hepatica infections in L. viatrix, in histological sections in which the presence of larval stages could not be observed through brightfield microscopy. The profiles generated were: stair bands referring to F. hepatica DNAmt amplification; a band of 1200 bp referring to L. viatrix ITS and another of 1300 bp referring to F. hepatica ITS and other trematodes. Multiplex-PCR has shown to be a fast, safe, highly sensitive and specific method, which is able to amplify DNA from fixed tissues, despite a low DNA quantity and its degradation caused by fixation processes. Such methodology may be useful in studies on fascioliasis epidemiology, enabling the use of material from histological collections.     

Effect of guar gum on glucose and lipid metabolism in white sea bream Diplodus sargus

The aim of this study was to assess the role of soluble non-starch polysaccharide (guar gum) on white sea bream Diplodus sargus, glucose and lipid metabolism. A control diet was formulated to contain 40 % crude protein, 14 % crude lipids and 35 % pregelatinized maize starch, and three other diets were formulated similar to the control diet except for guar gum, which was included at 4 % (diet GG4), 8 % (diet GG8) or 12 % (diet GG12). Diets were fed to the fish for 9 weeks on a pair-feeding scheme. Guar gum had no effect on growth performance, feed efficiency, glycaemia, cholesterolaemia and plasma triacylglyceride levels. Hepatic glucokinase and pyruvate kinase activities, liver glycogen content and liver insulin-like growth factor-I gene expression were not affected by dietary guar gum, while fructose-1,6-bisphosphatase activity was lower in fish fed guar gum–supplemented diets. Hepatic glucose-6-phosphate dehydrogenase activity was higher in fish fed diets GG4 and GG8 than in the control group. Overall, data suggest that in contrast to mammals guar gum had no effect on white sea bream glucose utilization and in lowering plasma cholesterol and triacylglyceride levels. However, it seems to contribute to lower endogenous glucose production.     

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 diet supplementation with white tea and methionine on lipid metabolism of gilthead sea bream juveniles (Sparus aurata)

A growth trial was performed with gilthead sea bream juveniles (Sparus aurata) to evaluate the effect of diet supplementation with white tea and methionine on fish performance and lipid metabolism. For that purpose, four diets were formulated: a fish meal–based diet (Control) and diets identical to the control diet but supplemented with 2.9 % white tea (Tea), 0.3 % methionine (Met) or 2.9 % white tea plus 0.3 % methionine (Tea + Met). Growth performance and feed efficiency parameters, whole-body and liver composition, plasma metabolites concentration and liver glucose 6-phosphate dehydrogenase (G6PDH), malic enzyme (ME) and fatty acid synthetase (FAS) activities were determined. Feed intake was higher in fish fed methionine–supplemented diets, whereas this parameter and growth was decreased in fish fed white tea supplementation. Feed efficiency and protein efficiency ratio were not affected by diet composition. Plasma HDL cholesterol and total lipids concentration were higher in fish fed white tea–supplemented diets. Whole-body lipid, plasma glucose, liver glycogen concentration and liver G6PDH, ME and FAS activities were lower in fish fed white tea–supplemented diets. Results of the present study indicate that methionine seems to act as a feed attractant in diets for sea bream juveniles. Additionally, white tea is an important modulator of lipid metabolism in sea bream juveniles.