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Rainbow trout were fed for 10 weeks with either a carbohydrate-free diet (C-free) or with four experimental diets containing various levels (20 or 40%) and sources of starch (extruded wheat or peas) in order to examine metabolic utilisation of dietary vegetable carbohydrates and its endocrine control. The study was focused on the parameters described as limiting in glucose metabolism in fish. Feeding trials were conducted at 8 and 18 °C to establish whether carbohydrate-rich diets can be used in trout farming irrespective of water temperature. At both temperatures, pea diets (especially the highest level) resulted in a feed efficiency as high as the C-free diet. Fish had similar growth rates except when fed the low wheat content diet. Glycaemia values 6 h after feeding were significantly higher in trout fed carbohydrate diets than those given the C-free diet, whereas plasma insulin levels were similar independently of the levels of dietary starch. This study provides the first evidence that glucokinase (GK) activity and mRNA level in trout liver increase in proportion to the content of dietary starch. Nevertheless, these changes were not correlated with plasma insulin levels. Insulin-like growth factor-I (IGF-I) binding and number of receptors in skeletal muscle were consistently higher than those for insulin but no diet-induced differences were found for any of these parameters. Temperature clearly affected the postprandial profile of glucose and insulin, which both showed lower levels 6 h after feeding at 8 °C than at 18 °C, which was consistent with a lower feed intake. Glucose and insulin levels decreased markedly 24 h after feeding at 18 °C, while they were still high at 8 °C, an observation concordant with delayed transit rate. These findings indicate satisfactory adaptation of rainbow trout to diets with a relatively high vegetable starch content, especially when provided as extruded peas, and indicate that diets with increased levels of carbohydrates can be used in this species even when it is reared at low temperature. [Copyright &y& Elsevier]

Abstract: The distribution of lipids in the flesh of large size brown trout (mean body weight 3.8±0.2 kg) was analyzed using magnetic resonance imaging (MRI) scanning. Assays were conducted with fish from a control line and from a line selected for growth rate, both fed a low- or a high-energy diet for 4 months. The MRI acquisition sequence used was 15 ms echo time (TE), 140 ms repetition time (TR) and 90° flip angle. Based on preliminary complete scanning of one fish, 15 different sections were defined in three areas designated by external anatomical references. The images were corrected for different scanning biases, and the voxel units were calibrated for lipid content of the flesh using external references. Values obtained through MRI matched well with those obtained by chemical and NMR analyses of lipid content (r2>0.91). Automated image analysis was conducted to calculate lipid content in the different muscle regions. Wide differences were observed, demonstrating both anteroposterior and central to periphery gradients. These differences are discussed in relation to tissue distribution, muscle activity and energy requirement for locomotion. There was no difference in lipid content or localization between the two lines. Feeding a high-energy diet resulted in significantly higher lipid deposition, especially in the anterior region of the muscle. [Copyright &y& Elsevier]

Two diets based on fish meal (FM) or on a mixture of plant protein sources supplemented with free amino acids (PP) were fed to rainbow trout having a mean initial body weight of 162.5 g reared at 17±1 °C for 24 weeks to evaluate the effect of plant protein sources on fish growth, morphological and body quality traits. At the end of the growth study, samples were withdrawn for chemical analyses as well as measurements of different parameters of quality.Compared to the FM group, the trout fed diet PP had lower growth rates (mean final body weight 663 vs. 800 g), feed efficiency (0.95 vs. 1.07) and protein efficiency ratio (1.96 vs. 2.13). Trout fed diet PP were also characterised by a lower dressed weight (89.45% vs. 91.07%), hepato-somatic index (0.92% vs. 1.01%) and fillet lipid content (5.50% vs. 6.98%), but had a higher mesenteric fat (5.65% vs. 4.08%), viscero-somatic index (10.55% vs. 8.93%) and fillet crude protein content (20.53% vs. 19.93%). The muscle fatty acid composition reflected that of the diet with a higher level of polyunsaturated (n-6) fatty acids in trout fed diet PP and a higher content in polyunsaturated n-3 fatty acids and n-3/n-6 ratio in trout fed diet FM. Sensory analysis was carried out at 5 days post-mortem on microwave-cooked dorsal portions of fillets stored at 1 °C with ice covering. The results of the triangular test showed differences between groups (P<0.01) in organoleptic characteristics as well as in visual colour. Descriptive tests pointed out that fillets of trout fed diet PP exhibited higher hardness, less sweetness and less odour intensity than trout fed diet FM.In summary, data show that long-term feeding a diet in which fish meal was totally replaced by a mixture of plant protein sources significantly affects growth and quality criteria such as morphometric traits, fat deposits, fillet chemical composition and organoleptic characteristics of large commercial size rainbow trout. [Copyright &y& Elsevier]

Abstract: A growth trial was conducted to test the growth potential and nutrient utilization of Senegalese sole fed diets with increasing substitution of supplemental fish oil (FO) by vegetable oil (VO) blends. Triplicate groups of twenty Senegalese sole juveniles (12g) were fed to satiation over a period of 12weeks with 6 extruded diets containing 570g protein/kg DM and 90g lipid/kg DM. Two blends of VO were tested (A and B) with two FO substitution rates 50% (VO50A and VO50B) and 100% (VO100A and VO100B). A concomitant replacement of 50% fish meal and 50% FO (VO50PP), and a control diet (CTR) containing only FO, were also evaluated. After 12-weeks feeding the dietary treatments did not affect growth performance and final body composition. Muscle eicosapentaenoic acid (EPA) was reduced in all treatments compared to CTR, but docosahexaenoic acid (DHA) was only reduced in the VO50PP group. FO substitution led to a general increase of muscle linoleic acid (18:2 n−6, LOA) with VO50PP inducing maximal levels (15% vs 6% in FO diet). Lipogenic enzymes (FAS, ME and G6PD) as well as long chain fatty acid elongation (elov5) and desaturation (Δ4 desaturase) were not affected by dietary treatments. Results suggest that Senegalese sole can cope with high levels of VO without compromising growth performance or nutrient utilization. Despite differences in muscle fatty acid profile, fish fillet had good nutritional value. [Copyright &y& Elsevier]

Abstract: Two lines of rainbow trout divergently selected for muscle fat content, fat line (F) and lean line (L) were used to investigate the effect of genetic selection on digestion, intestinal nutrient transport and fatty acid bioconversion, in relation to dietary starch intake. This study involved a digestibility trial for 2weeks using Cr2O3 as inert marker, followed by a feeding trial for 4weeks. For the entire duration, juvenile trout from the two lines were fed diets with or without gelatinized starch. Blood, pyloric ceca, midgut and hindgut were sampled at 24h after the last meal. Transcripts of the proteins involved in nutrient transport and fatty acid bioconversion were abundant in the proximal intestine. GLUT2 transcripts were slightly higher in the F line ceca than in the L line. Dietary starch intake did not enhance the transcription of intestinal glucose transporters, SGLT1 and GLUT2; but it was associated with the higher expression of ApoA1 and PepT1 in the midgut. Significantly, the F line exhibited higher intestinal mRNA levels of MTP, ApoA4, Elovl2, Elovl5 and D6D than the L line, linked to chylomicron assembly and fatty acid bioconversion. Apparent digestibility coefficients of protein, lipid and starch were high in both lines, but not significantly different between them. In conclusion, we found a higher potential of chylomicron synthesis and fatty acid bioconversion in the intestine of F line, but no adaptive transcriptional response of glucose transporters to dietary starch and no genotypic differences in nutrient digestibility. [Copyright &y& Elsevier]

Abstract: In the last years, the increase of aquaculture production has led to the evolution of feed composition with an increasing substitution of fish meal and fish oil with terrestrial plant products. In the meantime, selective breeding of fish has been widely developed. The ability to grow on plant-based diets has recently been proven to be genetically variable, pointing out the interest to increase knowledge on the potential consequences of substitution of fish meal and fish oil on current breeding programs. Moreover, heritabilities of major production traits other than growth also need to be estimated in this new environment. Experimental rainbow trouts (about 3000) were derived from a factorial mating design (25 sires and 10 dams), separated in two batches and fed two experimental diets since the first meal. The marine diet (M) was based on fish meal (FM) and fish oil (FO), while the substitution rate by plant products was total in the plant-based (PB) diet (free of FM and FO). We estimated heritabilities under both diets and genotype by diet interactions for body weight, fork length, condition factor, TGC (thermal-unit growth coefficient) and processing yields: viscera yield, carcass yield, filet yield and head yield. Due to the reduced growth of fish fed the plant-based diet, the estimation of genetic parameters was done on fish from both dietary treatments measured at the same age and also on fish measured at the same weight assuming that family rankings could evolve with further growth. Survival rates were high and did not depend on the diet. At 343days, the body weight of the M batch (440.2g±11.3) was twice that of the PB batch (216.0g±12.6). After 465days, the PB batch reached 407.4g±17.1. Whatever the comparison (at same age or same weight), there were significant diet-induced differences for processing traits except for head yield (P =0.80, same age) and filet yield (P =0.82, same weight). The main findings are the high heritabilities observed in fish fed the plant-based diet for body weight (0.69±0.13), TGC (0.65±0.12) and the generally low, though significant, genotype by diet interactions for final body weight, fork length, carcass yield, viscera yield, head yield and filet yield between fish fed source-contrasted diets. Estimates of genetic correlation between diets were the lowest for early weight (0.67±0.12) and indicate differential abilities for initial growth between M and PB diets. [Copyright &y& Elsevier]

Abstract: In mammals, carnitine palmitoyltransferase 1 (CPT1) is a rate limiting enzyme of fatty acid oxidation. Two isoforms are present. We characterized a full-length cDNA sequence encoding chicken liver L-CPT1 isoform and a partial cDNA sequence encoding chicken muscle M-CPT1 isoform. CPT1 messengers showed the expected tissue specificity. M-CPT1 messenger and CPT1 activity were higher in oxidative than in glycolytic muscle. Expression of both isoforms was assessed in various tissues of genetically fat or lean chickens. Fasting considerably increased L-CPT1 mRNA expression and β-hydroxyacyl CoA dehydrogenase (HAD) activity in the liver of fat or lean chickens. Unexpectedly, fasting did not increase M-CPT1 mRNA levels nor HAD activity in muscles of either chicken genotype. It however increased succinyl-CoA:3-ketoacid CoA transferase (SCOT) mRNA expression (an enzyme related to ketone body utilization) in oxidative muscle. SCOT messenger was slightly more abundant in oxidative muscle of lean chickens but not in glycolytic muscle. In conclusion, the regulation of fatty acid oxidation is probably not impaired in fat chicken. The absence of fasting stimulation of M-CPT1 mRNA expression, which is at variance with the situation observed in mammals, suggests that during fasting, chicken muscles preferentially use ketone bodies as fuel, at least in the short term. [Copyright &y& Elsevier]

The role of somatolactin (SL) in the regulation of energy homeostasis in gilthead sea bream (Sparus aurata) has been analysed. First, a down-regulation of plasma SL levels in response to gross shifts in dietary amino acid profile and the graded replacement of fish meal by plant protein sources (50%, 75% and 100%) has been observed. Thus, the impaired growth performance with changes in dietary amino acid profile and dietary protein source was accompanied by a decrease in plasma SL levels, which also decreased over the course of the post-prandial period irrespective of dietary nitrogen source. Secondly, we examined the effect of SL and growth hormone (GH) administration on voluntary feed intake. A single intraperitoneal injection of recombinant gilthead sea bream SL (0.1 μg/g fish) evoked a short-term inhibition of feed intake, whereas the same dose of GH exerted a marked enhancement of feed intake that still persisted 1 week later. Further, we addressed the effect of arginine (Arg) injection upon SL and related metabolic hormones (GH, insulin-like growth factor-I (IGF-I), insulin and glucagon) in fish fed diets with different nitrogen sources. A consistent effect of Arg injection (6.6 μmol/g fish) on plasma GH and IGF-I levels was not found regardless of dietary treatment. In contrast, the insulinotropic effect of Arg was found irrespective of dietary treatment, although the up-regulation of plasma glucagon and glucose levels was more persistent in fish fed a fish meal based diet (diet FM) than in those fed a plant protein diet with a 75% replacement (diet PP75). In the same way, a persistent and two-fold increase in plasma SL levels was observed in fish fed diet FM, whereas no effect was found in fish fed diet PP75. Taken together, these findings provide additional evidence for a role of SL as a marker of energy status, which may be perceived by fish as a daily and seasonal signal of abundant energy at a precise calendar time. [Copyright &y& Elsevier]

The carnitine palmitoyltransferase I (EC.2.3.1.21; CPT I) mediates the transport of fatty acids across the outer mitochondrial membrane. In mammals, there are two different proteins CPT I in the skeletal muscle (M) and liver (L) encoded by two genes. The carnitine palmitoyltransferase system of lower vertebrates received little attention. With the aim of improving knowledge on the CPT family in fish, we examined CPT I cDNA and CPT activity in different tissues of rainbow trout (Oncorhynchus mykiss). Using RT-PCR, we successfully cloned a partial CPT I cDNA sequence (1650 bp). The predicted protein sequence revealed identities of 63% and 61% with human L-CPT I and M-CPT I, respectively. This mRNA is expressed in liver, white and red skeletal muscles, heart, intestine, kidney and adipose tissue of trout. This is in good agreement with the measurement of the CPT activity in the same tissues. The [IC50] that reflects the sensitivity to malonyl-CoA inhibition was 0.116±0.004 μM for the liver and 0.426±0.041 μM for the white muscle. These results demonstrate for the first time the existence of at least one gene encoding for CPT I present in both the liver and the muscle of rainbow trout. [Copyright &y& Elsevier]