Geneviève Corraze

Regulation of hepatic lipogenesis by dietary protein/energy in juvenile European seabass (Dicentrarchus labrax)

Abstract A growth trial was conducted with groups of European seabass having an initial weight of 6 g to study the lipogenic action of dietary protein and non-protein energy supplies. Six experimental diets were formulated to contain one of two crude protein levels (43 and 52%) with digestible protein (DP) to digestible energy (DE) ratios ranging from 19 to 26 mg/kJ. At the end of the growth trial (12 weeks), the activities of liver glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49), malic enzyme (ME, EC 1.1.1.40), ATP citrate lyase (ACL, EC 4.1.3.8), acetyl-CoA carboxylase (ACoAC, EC 6.4.1.2) and fatty acid synthetase (FAS, EC 2.3.1.38) were measured. Digestibility of main dietary components was also determined over a three-week period. At each protein level, an increase in dietary DE led to improved growth performance, protein efficiency, daily N deposition and to a reduction of N loss. Best results were achieved at 40% DP and a DP/DE ratio of 19–20 mg/kJ. G6PD, ME and ACoAC were found to be the key regulatory enzymes in the lipogenic pathway, with G6PD being the main NADPH-generating enzyme. Activities of G6PD, ME, ACL and FAS were reduced with increasing fat intake. Activities of G6PD, ME and ACL were increased with increasing starch intake. ACoAC activity was negatively correlated with starch intake and positively with fat intake.

Effects of dietary amino acid profile on growth performance, key metabolic enzymes and somatotropic axis responsiveness of gilthead sea bream (Sparus aurata)

Abstract Juvenile gilthead sea bream were fed to visual satiety with isonitrogenous diets based on fish meal and different plant ingredients (33–35% replacement) supplemented with free amino acids to meet the desired indispensable amino acid (IAA) profile and dispensable amino acid (DAA) content. In diets M and WB, IAA profile and DAA content resemble that of the muscle or whole body, respectively. In diets MGlu and WBGlu, DAA content was increased by adding l -glutamic acid (Glu) and thus the IAA/DAA ratio varied from 1.13 (diet M) to 0.80 (diet WBGlu). Growth rates were not significantly different among experimental groups, but feed conversion ratio and nitrogen retention were impaired by the decrease of dietary IAA/DAA ratio. Postprandial ammonia excretion increased with the increase of dietary DAA content irrespective of IAA profile. Conversely, hepatic activity of glutamate dehydrogenase (GDH) was lower in fish fed diet WBGlu than in fish fed diet M. Hepatic growth hormone (GH) binding was not significantly affected by the dietary treatment, but circulating levels of insulin-like growth factor-I (IGF-I) and GH were, respectively, down- and up-regulated in fish fed diet WBGlu, which suggests some defect in the transmission of GH receptor signal. Fat retention and hepatic activities of lipogenic enzymes (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME) were decreased in fish fed diet MGlu. Key metabolic enzymes of hepatic glycolysis (glucokinase, GK) and gluconeogenesis (phosphoenolpyruvate carboxykinase, PEPCK) were also altered in this group of fish. Since soybean meal concentration was highest in diet MGlu, results on lipid and carbohydrate metabolism can be primarily attributed to this component of the diet. In contrast, data on growth performance, ammonia excretion and GH axis mainly reflect changes in the dietary amino acid profile, which reveals that a muscle IAA profile and a high IAA/DAA ratio are important in feeds for gilthead sea bream.

Cloning and nutritional regulation of a Δ6-desaturase-like enzyme in the marine teleost gilthead seabream (Sparus aurata)

Marine fish are presumed to have a lower capacity than freshwater fish for the bioconvertion of 18C fatty acids into 20-22C highly unsaturated fatty acids (HUFA). The present work investigated the first step of this pathway, the Delta6-desaturation, in gilthead seabream. A full-length desaturase-like cDNA was identified from total RNA extracted from viscera of juvenile fish fed for 96 days on an experimental HUFA-free diet containing olive oil as the sole lipid source. The open reading frame encodes a 445-amino acid peptide that contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain, which are characteristic of Delta6- and Delta5-desaturases. Predicted protein sequence of seabream desaturase-like indicated a high percentage of identity with mammalian Delta6-desaturases (approx. 65%). Northern analysis showed two transcripts of approximately 3.7 and 1.8 kb which were highly expressed in fish fed on HUFA-free diet and slightly expressed in fish fed on HUFA-rich diet. The fatty acid profile of the former group was characterized by high levels of Delta6-desaturation products (18:2 n-9 and 20:2 n-9) with no detectable levels of Delta5-desaturation product (20:3n-9). These results demonstrate for the first time the presence and nutritional modulation of a Delta6-desaturase-like cDNA in a marine fish.

Incorporation of high levels of extruded lupin in diets for rainbow trout (Oncorhynchus mykiss): nutritional value and effect on thyroid status

Three experiments and a digestibility trial were conducted in order to assess the incorporation of extruded lupin (Lupinus albus) in diets for juvenile rainbow trout. Digestibility of protein and phosphorus were higher in lupin than in fish meal, but digestibility of dry matter and energy were lower. The first trial was designed to determine the maximum level of incorporation of lupin in the diet of trout. Levels of 30, 50 and 70% were tested and compared with a fish meal-based control diet. The diets were formulated to be isonitrogenous and isoenergetic. Triplicate groups of trout were fed twice daily to visual satiety by hand during 64 days. Two subsequent trials, using another yearly crop of lupin, were performed to analyze the effects of very high levels of incorporation of lupin. Growth performances, feed intake and nitrogen balance of fish fed diets with 50% of lupin incorporation were comparable to those of fish fed the control diet. However, higher fat deposition was observed. Incorporation of lupin led to higher phosphorus retention and lower phosphorus excretion, but only in two of the three trials. In trout fed the diets containing 70% lupin, growth was reduced by 41%, feed intake by 15% and nitrogen retention by 12% when the first crop of lupin was used. Feed intake was not reduced and growth performance was higher when the second crop of lupin was used, i.e., a decrease of only 16% when fish were fed by hand to satiety (decrease of feed efficiency) or null when fish were fed on demand using self-feeders. The incorporation of lupin can lead to a decrease in plasma thyroxine levels, but this effect was not clear and not recurring. However, when this effect was observed, a deiodinase compensatory effect adjusted the plasma triiodothyronine levels. In general, the plasma triiodothyronine levels were related to the growth performance of the trout.

Digestibility, postprandial ammonia excretion and selected plasma metabolites in European sea bass (Dicentrarchus labrax) fed pelleted or extruded diets with or without wheat gluten

Abstract The effects of diet processing technology on digestibility, postprandial ammonia excretion rates and plasma concentration of ammonia, glucose and cholesterol (CHOL) were determined in European sea bass. Four dietary treatments were compared: diet E0 (extruded basal fish meal diet); diet P0 (pelleted basal fish meal diet); diet E30 (extruded, 70% basal diet plus 30% wheat gluten) and diet P30 (pelleted, 70% basal diet plus 30% wheat gluten). Each dietary treatment was assigned to triplicate groups of fish (body weight: 200 g). Levels of ammonia-N excretion from fish fed the different diets were measured in water samples taken from culture tanks every 2 h. At the end of the experiment, plasma samples from 3 fish per diet, taken in alternative tanks every 2 h during 24 h, were assayed for ammonia, glucose and cholesterol determination. Nutrient digestibility was not affected by the diet processing methods used. Wheat gluten showed high apparent digestibility coefficient (ADC) values for protein, energy and organic matter. Postprandial ammonia excretion values showed maximum values between 4 and 10 h after the meal depending on treatment. Daily cumulative total ammonia excretion rates were lower in fish fed fish meal based diets than in those fed diets containing 30% wheat gluten. Irrespective of dietary formulation, fish fed extruded diets showed lower ammonia excretion than those fed the dry pelleted diets. Postprandial values for plasma ammonia ranged between 3 and 8 mg ml−1 and the pre-feeding values were reached 24 h after feeding in all treatment groups. Maximal levels of plasma glucose (120–180 mg ml−1) appeared within 6 to 10 h after feeding. Plasma cholesterol levels were lower in sea bass fed diets containing 30% wheat gluten than in those fed diets containing fish meal alone as the dietary protein source.

Effects of restricted ration, time-restricted access and reward level on voluntary food intake, growth and growth heterogeneity of rainbow trout (Oncorhynchus mykiss) fed on demand with self-feeders

Abstract Growth responses of rainbow trout fed on demand using self-feeders were tested over an 8 week period when triplicate groups were exposed to two feeding levels (unlimited and fixed ration), at two feeding frequencies (time-restricted and free access) and three reward levels (0.17 g, 0.30 g and 0.43 g per trigger actuation). Triplicate groups were also hand fed as control of maximum growth. Each fish was marked according to its weight-class, and each group of 26 fish comprised a predetermined number of fish per weight-class: two fish of 13–16 g, six fish of 16–19 g, 10 fish of 19–22 g, six fish of 22–25 g and two fish of 25–28 g. There was no significant effect of feeding regime on feed efficiency. Voluntary feed intake and specific growth rates were significantly decreased as fish were exposed to reduced reward levels, even though there was a negative relationship between reward level and daily demand. Time-restricted access to self-feeders led to a decrease in feed intake, and an increase in growth heterogeneity in comparison with free access to self-feeders. Voluntary feed intake and specific growth rates were always lower in self-fed groups than in groups fed to apparent satiation by hand. Individual growth heterogeneity was greater within tanks allowed time-restricted access to self-feeders and within tanks fed by hand to visual satiation than within those given continuous access to self feeders. It is suggested that rainbow trout fed on demand with self feeders may not ingest as much food as they would be able to, and may not be satiated, but do express their hunger in relation with the level of effort that has to be done to obtain food.

Effects of dietary levels of carbohydrate and lipid on glucose oxidation and lipogenesis from glucose in rainbow trout, Oncorhynchus mykiss, reared in freshwater or in seawater

Carbon dioxide production and lipogenesis from U-14C-glucose were studied in vivo in trout fed three experimental diets varying in their carbohydrate-to-lipid ratio (266, 2410, 2114) and grown either in freshwater or in seawater. 14CO2 production from U-14C-glucose, was higher with the intermediary diet in trout reared in seawater. Lipogenesis from U-14C-glucose increased with increasing dietary carbohydrate-to-lipid ratio, particularly for the phospholipids, triacylglycerols and fatty acids, but this effect varied according to rearing conditions. The results indicate that dietary regulation of lipogenesis in trout has some similarities with that observed in homeotherms and that salinity and/or fish weight interacts with this regulation.

Effects of dietary medium-chain triacylglycerols (tricaprylin and tricaproin) and phospholipid supply on survival, growth and lipid metabolism in common carp (Cyprinus carpio L.) larvae

Abstract The present study investigated the interaction of dietary medium-chain fatty acids (MCFA) and phospholipids (PL) on survival, growth and lipid metabolism in common carp larvae. Nine diets based on casein and dextrin and with a variable lipid part were tested in triplicate for 22 days post first feeding. The 3×3 design consisted of three triacylglycerols (3% of diet) combined with three different lipid supplements. Tested triacylglycerols were triolein (TOL), tricaprylin (TC8) and tricaproin (TC6), and lipid supplements were 2% soybean oil (low-fat diets without PL), 2% soybean lecithin (low-fat diets with 2% PL) or both 2% soybean lecithin and 6% TOL (high-fat diets with 2% PL). In the first step, both TC6 and TC8 resulted in improved survival and growth rates compared to TOL, irrespective of the PL supply. In the second step, TC8 decreased survival and growth rates, whereas the difference between TC6 and TOL became less. Histological signs of impaired intestinal absorption of neutral lipids were evidenced in larvae fed TOL without PL and also in high-fat diets with 2% PL. The latter diets also resulted in poorer growth rates compared to low-fat diets with 2% PL. These results suggest that the quantitative PL requirement of larvae increases as the dietary level of long-chain triacylglycerols increases. Larvae fed TC6 or TC8 showed enlarged liver and hepatocyte volume and a decreased level of body neutral lipids. Based on β-hydroxybutyrate (β-HBA) measurements in whole larvae, TC8 was found to be more ketogenic than TC6. TC6 and TC8 affected differently the fatty acid profile of larval body neutral lipids. TC6 did not induce the appearance of MCFA, whereas TC8 feeding resulted in a low level of 8:0 and relatively high levels of 10:0 (3.8% of total fatty acids). Neither 8:0 nor 10:0 were found in larval polar lipids. This study confirmed the essentiality of PL in common carp larval diets and underlines differences in the utilization of TC6 and TC8, which both initially stimulate growth during the first week, but only temporarily in the case of TC8.

Effect of coconut oil and tricaprylin vs. triolein on survival, growth and fatty acid composition of / common carp Cyprinus carpio L. larvae

Abstract A 21-day feeding trial was carried out to investigate the ability of first-feeding carp larvae to utilize medium-chain fatty acids (MCFA). Six semi-purified diets, with a common casein and soluble fish protein concentrate basis, were tested on triplicate groups of 400 larvae. The diets were isolipidic (23–24% of dry matter). They differed only by triacylglycerol supplementation (10% of diet) which consisted of either triolein (TO), coconut oil (CO) or tricaprylin (TC) alone or in combination of two of these (TO+CO, CO+TC, TO+TC). Survival and growth rates of larvae fed with CO or TO were high (survival 95–97%, mean wet weight 60–67 mg after 21 days). Addition of TC (5 or 10% of diet) induced a significant mortality as early as 11 days of feeding and resulted in a final survival of less than 6%. TC also led to reduced growth rates (final mean larval weight 6–13 mg). The fatty acid (FA) composition of larvae fed with TO or CO reflected that of the diets with high levels of oleic acid (42% of total FA) in larvae fed with TO and lauric and myristic acids (17 and 10% of total FA, respectively) in larvae fed with CO. In contrast, larvae fed with TC contained only traces (0.3% of total FA) of caprylic acid but had higher levels of capric acid than other larvae (6% vs. 1–2%). Present results indicate an important difference in the utilization between MCFA supplied as CO (12:0) and TC (8:0).

ESTIMATION OF ESSENTIAL FATTY ACID REQUIREMENTS OF COMMON CARP LARVAE USING SEMI-PURIFIED ARTIFICIAL DIETS

Two trials were conducted with duplicate groups of (first feeding) carp larvae fed artificial dry diets based on casein and dextrin over 21 or 25 days. One control diet based on yeast was also tested. Survival, growth and fatty acid profiles of larvae were studied. In trial 1, (n-3) fatty acid requirement was estimated using diets supplemented or not with methyl linolenate or cod liver oil. After 21 days, the best survival and growth were observed in larvae fed the unsupplemented diet [(n-3) fatty acid level: 0.05%]. Survival and growth were not improved by higher levels of (n-3) fatty acids. In trial 2, (n-6) fatty acid requirement was estimated using diets with graded levels of methyl linolenate or peanut oil. After 25 days, the best survival and growth were obtained with diets supplemented with 0.25% methyl linolenate (total (n-6) fatty acid level: 1%) or with 1.25% peanut oil (total (n-6) fatty acid level: 0.89%). Survival and growth were not improved by higher levels of (n-6) fatty acids. Fatty acid composition of carp reflected that of the diets and also showed that carp larvae are capable of elongating and desaturating linolenic acid and linoleic acid in longer chain fatty acids.