Effects of training on lipid metabolism in swimming muscles of sea trout (Salmo trutta)

Improving the Aerobic Capacity in Fingerlings of European Sea Bass (Dicentrarchus labrax) through Moderate and Sustained Exercise: A Metabolic Approach

Sustained swimming induces beneficial effects on growth and energy metabolism in some fish species. However, the absence of a standardized exercise regimen that guarantees an optimal response to physical activity is due to the anatomical, behavioral, and physiological differences among species, and the different conditions of tests applied, which are especially notable for the early stages of cultured species. The objective of this study was to assess the growth and metabolic responses of European sea bass submitted to continuous and moderate exercise exposure, selecting a practical swimming speed from swimming tests of groups of five fingerlings. The exercise-effects trial was carried out with 600 sea bass fingerlings (3-5 g body weight) distributed in two groups (control: voluntary swimming; exercised: under sustained swimming at 1.5 body lengths·s-1). After 6 weeks, growth parameters and proximal composition of both muscles were not altered by sustained swimming, but an increased synthetic capacity (increased RNA/DNA ratio) and more efficient use of proteins (decreased ΔN15) were observed in white muscle. The gene expression of mitochondrial proteins in white and red muscle was not affected by exercise, except for ucp3, which increased. The increase of UCP3 and Cox4 protein expression, as well as the higher COX/CS ratio of enzyme activity in white muscle, pointed out an enhanced oxidative capacity in this tissue during sustained swimming. In the protein expression of red muscle, only CS increased. All these metabolic adaptations to sustained exercise were also reflected in an enhanced maximum metabolic rate (MMR) with higher aerobic scope (AMS) of exercised fish in comparison to the non-trained fish, during a swimming test. These results demonstrated that moderate sustained swimming applied to sea bass fingerlings can improve the physical fitness of individuals through the enhancement of their aerobic capacities.

Diversity analysis of hilsa (Tenualosa ilisha) gut microbiota using culture-dependent and culture-independent approaches

AIMS

The bacterial communities associated with the gastrointestinal (GI) tract are primarily involved in digestion, physiology, and the immune response against pathogenic bacteria for the overall development and health of the host. Hilsa shad (Tenualosa ilisha), a tropical anadromous fish, found predominantly in Bangladesh and India, has so far been poorly investigated for its gut bacterial communities. In this study, both culture-based and metagenomic approaches were used to detect intestinal isolates of hilsa, captured from both freshwater and seawater to investigate the community structure of intestinal microbiota.

METHODS AND RESULTS

Culture-dependent approach allowed to isolate a total of 23 distinct bacterial species comprising 16 Gram-negative, and 7 Gram-positive isolates, where Proteobacteria and Firmicutes were identified as the two most dominant phyla. While metagenomic approach explored a wide range of important GI bacteria, primarily dominated by Proteobacteria, Firmicutes, and Bacteroidetes, with Proteobacteria and Firmicutes, being the most abundant in freshwater and seawater samples, respectively.

CONCLUSIONS

A combination of these approaches provided the differential GI-associated bacterial diversity in freshwater and seawater hilsa with the prediction of overall functional potential.

IMPACT STATEMENT

The study explored the diversity of gut microbiota in hilsa, one of the most preferred nutritious dietary fish, captured from freshwater and seawater habitats, which may encourage to comprehend the composition of the gut microbiome in relation to the migratory behavior and polyunsaturated fatty acid profile of anadromous fish in general.

Swimming training combined with chitosan supplementation reduces the development of obesity and oxidative stress in high-fat diet-fed mice

Obesity is often introduced as one of the metabolic disorders caused by imbalance between energy consumption and metabolisable energy intake. Experts in the field considered obesity as one of the robust risk factors for the lifestyle-associated diseases. The present research examined interventional effects of marine chitosan (CS), swimming training (ST) and combination of CS and ST (CS + ST) in the mice fed with high-fat diets (HFD). In this study, sample size was considered more than three in groups. Forty mice were randomly divided into five groups (n 8 per group) including control group (received the standard diet), HFD group (received high-fat food with 20 % fat), HFD + CS group (treated with high-fat food with 5 % CS), HFD + ST group (treated with HFD and ST) and HFD + CS + ST group (treated with high-fat food with 5 % CS and ST). After 8 weeks, the blood glucose, oxidative stress (OS) and lipid profile were measured. The results showed that CS + ST group has more effects in the control of body weight with the increased concentration of HDL-cholesterol, OS inhibition via enhancing the body antioxidant capacity in comparison with the ST or CS alone in HFD-fed mice. Moreover, lipid profile was improved in CS + ST-treated mice compared with HFD-treated mice, and OS inhibition correlated with the greater activities of the antioxidant enzyme enhances the lipid oxidation, cholesterol and fatty acid homoeostasis. The results suggested that a dietary intervention with a combined ST and CS can be a feasible supplementary for human prevention of obesity.

Lotic Environment Affects Morphological Characteristics and Energy Metabolism of Juvenile Grass Carp Ctenopharyngodon idella

This study investigated the effect of a lotic environment on morphological characteristics and energy metabolism in juvenile grass carp Ctenopharyngodon idella. The fish were stocked in the lotic environment and forced to swim for 12 h per day for 4 weeks at three water current velocities of 0.5, 2, and 4 body length s−1 (Bl s−1). The control fish were stocked in the lentic environment with water current velocities of 0 Bl s−1. The results showed that lotic environment significantly increased body weight, body length, and condition factor of grass carp. The first principal component (PC1) characterized by measured overall body size suggested that fish in a lotic environment had body stoutness and wider tail stalk. Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic swimming performance (Ucrit) were elevated with the increased water flow and positively correlated with PC1. The 4 Bl s−1 group showed significantly decreased contents of serum glucose and muscular glycogen, and a significantly increased level of serum lactic acid. The mRNA expression levels of AMP-activated protein kinase-phosphorylate PPAR γ coactivator 1 α-nuclear respiratory factor 1 (AMPK-PGC1α-NRF1) pathway-related genes were significantly upregulated in red muscle of grass carp in the lotic environment. Water flow environment at 4 Bl s−1 significantly increased ratios of metabolic enzymes (lactate dehydrogenase/citrate synthase) and cytochrome c oxidase/citrate synthase) in the muscle. The relationship between morphological characteristics and metabolic capacity suggested that the body size of grass carp in a lotic environment was shaped to promote energy metabolism. The study identified the evidence of the mechanism and relationship of the trade-off between energy and morphology in grass carp.

Sustained swimming exercise training decreases the individual variation in the metabolic phenotype of gilthead sea bream (Sparus aurata)

Cultured fish can be induced to swim, although the suitability and benefits remain to be tested. Sustained swimming exercise (SSE) training and detraining (DET) were applied in juvenile gilthead sea bream (Sparus aurata) and the metabolic rates were investigated. Fish with a total body mass of 80.5 ± 1.5 g and total length 17.2 ± 0.1 cm were maintained untrained (spontaneously swimming activity, UNT), swim-trained (induced sustained swimming activity, SSE) at 1 BL s^-1 for 28 days, or detrained (28 days of swimming followed by 10 days of untraining, DET). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and excess post-exercise oxygen consumption (EPOC) were assessed (n = 10). In addition, the effects of SSE training (51 days) on blood and plasma parameters were investigated before and immediately after applying a high-intensity swimming (HIS) protocol. SMR, MMR, and EPOC values were not different between SSE, UNT, or DET fish (143.2, 465.5 mg O₂ kg^-1 h^-1, and 459.1 mg O₂ kg^-1, respectively). Spite the lack of differences between treatments, the dispersion in the residuals for SMR, MMR, and absolute aerobic scope (AAS) values followed the order UNT > DET > SSE, indicating that swim training decreases the individual variation of these metabolic parameters. Haematological parameters, plasma glucose, lactate, and cortisol levels were similar between SSE and UNT groups before HIS. Plasma glucose and lactate levels increased in both groups after HIS, being higher in the SSE group. Plasma cortisol levels were similar between both groups after HIS. Results suggest that SSE training improves energy use and reduces individual variation in SMR and MMR, an effect that declines with detraining.

Mitochondrial Adaptation to Diet and Swimming Activity in Gilthead Seabream: Improved Nutritional Efficiency

Sustained exercise promotes growth in different fish species, and in gilthead seabream we have demonstrated that it improves nutrient use efficiency. This study assesses for differences in growth rate, tissue composition and energy metabolism in gilthead seabream juveniles fed two diets: high-protein (HP; 54% protein, 15% lipid) or high energy (HE; 50% protein, 20% lipid), under voluntary swimming (VS) or moderate-to-low-intensity sustained swimming (SS) for 6 weeks. HE fed fish under VS conditions showed lower body weight and higher muscle lipid content than HP fed fish, but no differences between the two groups were observed under SS conditions. Irrespective of the swimming regime, the white muscle stable isotopes profile of the HE group revealed increased nitrogen and carbon turnovers. Nitrogen fractionation increased in the HP fed fish under SS, indicating enhanced dietary protein oxidation. Hepatic gene expression markers of energy metabolism and mitochondrial biogenesis showed clear differences between the two diets under VS: a significant shift in the COX/CS ratio, modifications in UCPs, and downregulation of PGC1a in the HE-fed fish. Swimming induced mitochondrial remodeling through upregulation of fusion and fission markers, and removing almost all the differences observed under VS. In the HE-fed fish, white skeletal muscle benefited from the increased energy demand, amending the oxidative uncoupling produced under the VS condition by an excess of lipids and the pro-fission state observed in mitochondria. Contrarily, red muscle revealed more tolerant to the energy content of the HE diet, even under VS conditions, with higher expression of oxidative enzymes (COX and CS) without any sign of mitochondrial stress or mitochondrial biogenesis induction. Furthermore, this tissue had enough plasticity to shift its metabolism under higher energy demand (SS), again equalizing the differences observed between diets under VS condition. Globally, the balance between dietary nutrients affects mitochondrial regulation due to their use as energy fuels, but exercise corrects imbalances allowing practical diets with lower protein and higher lipid content without detrimental effects.

Dietary linoleic acid, antioxidants, and flight training influence the activity of oxidative enzymes in European Starlings (Sturnus vulgaris)

Multiple studies have demonstrated that diet (e.g., fatty acid composition, antioxidants) and exercise training affect the metabolic performance of songbirds during aerobic activity, although the physiological mechanisms that cause such an effect remain unclear. We tested the hypothesis that elevated proportions of dietary linoleic acid (18:2n6) and amounts of dietary anthocyanins (a hydrophilic antioxidant class) influence the activity and protein expression of oxidative enzymes in flight and leg muscle of European Starlings (Sturnus vulgaris N = 96), a subset of which were flown over 15 days in a wind tunnel. Carnitine palmitoyl transferase (CPT) and citrate synthase (CS) activity displayed 18:2n6-dependent relationships with soluble protein concentration. Lactate dehydrogenase (LDH) was similarly related to protein concentration although also dependent on both dietary anthocyanins and flight training. 3-Hydroxyacyl CoA Dehydrogenase (HOAD) activity increased throughout the experiment in flight muscle, whereas this relationship was dependent on dietary anthocyanins in the leg muscle. Soluble protein concentration also increased throughout the experiment in the flight muscle, but was unrelated to date in the leg muscle, instead being influenced by both dietary anthocyanins and flight training. Training also produced additive increases in CPT and leg muscle HOAD activity. FAT/CD36 expression was related to both dietary 18:2n6 and training and changed over the course of the experiment. These results demonstrate a notable influence of our diet manipulations and flight training on the activity of these key oxidative enzymes, and particularly CPT and CS. Such influence suggests a plausible mechanism linking diet quality and metabolic performance in songbirds.

Feeding Faba Beans (Vicia faba L.) Reduces Myocyte Metabolic Activity in Grass Carp (Ctenopharyngodon idellus)

In this study, we aimed to explore the effects of faba bean (Vicia faba L.) on the energy metabolism of grass carp (Ctenopharyngodon idellus). A total of 180 fish (∼2900 g) were randomly assigned to six tanks (2.5 × 2.5 × 1.2 m; 30 individuals per tank) and fed either faba bean (Vicia faba L.) or a commercial diet for 120 days (3% body weight, twice per day). The results showed that faba bean-fed grass carp (FBFG) had significantly lower growth and higher fat accumulation in the mesenteric adipose tissue and hepatopancreas than commercial diet-fed grass carp (CDFG). Compared with CDFG, FBFG exhibited no significant difference in proximate composition of the muscle; however, an obvious decrease in muscle fiber size and significantly higher hardness, chewiness, and gumminess were observed. Transcriptome results showed that a total of 197 genes were differentially regulated in the dorsal muscle. Down-regulated genes included four genes annotated with myocyte development and 12 transcripts annotated with components of myofibrils. In addition, the FBFG group exhibited significantly lower expression of genes associated with oxygen transport, the mitochondrial respiratory chain, and creatine metabolism, suggesting reduced energy availability in the muscle of the FBFG. Moreover, using western-blotting and enzyme assays, we found decreased protein levels in the mitochondrial electron transport respiratory chain and creatine metabolism activities, as well as increased expression of autophagy marker protein levels, in the muscle of FBFG. Overall, our results suggest that an abnormal energy distribution may exist in grass carps after feeding with faba bean, which is reflected by a mass of fat deposition in the adipose tissue and hepatopancreas and subdued metabolic activity in the muscle.

Effect of sustained training on glycolysis and fatty acids oxidation in swimming muscles and liver in juvenile tinfoil barb Barbonymus schwanenfeldii (Bleeker, 1854)

The present study examines the effect of sustained exercise on glycolysis and fatty acids oxidation in the swimming muscles and liver in juvenile tinfoil barb (Barbonymus schwanenfeldii). The subjects were divided into one control group (water current speed of 0.0 bl s^-1, body length per second) and two training groups (1.0 and 2.0 bl s^-1), respectively. Results showed that the glycolysis was stimulated by high-speed training in the white muscle, accompanied by significantly increased activities of hexokinase, pyruvate kinase, and reduction in glycogen contents in training groups (P < 0.05). On the contrary, the extreme fatty acids oxidation was observed in the red muscle in high-speed training group, showed significant reduction in crude lipid content with a significant increase in the activities of hormone-sensitive lipase, β-hydroxyacyl-CoA dehydrogenase, and cytochrome C oxidase in 2.0 bl s^-1 group (P < 0.05). In addition, the saturated fatty acids in the red muscle and monounsaturated fatty acids in the white muscle were used preferentially during sustained training, respectively. Furthermore, the glycogen content within the liver was also significantly reduced with increasing training intensities (P < 0.05). These results suggested that glycogen and fatty acids were all used as a fuel to support sustained swimming in two functional muscles in B. schwanenfeldii, but higher glycolysis and fatty acids oxidation were seen in white and red muscles during high-speed swimming, respectively. Furthermore, the hepatic glycogen played an important role in the supply of energy in sustained training periods in B. schwanenfeldii.

A metabolomic study of fipronil for the anxiety-like behavior in zebrafish larvae at environmentally relevant levels

Field residue of fipronil can interfere with the physiological characters of the domesticated fish; thus, lethal dose test and the general biomarker cannot delineate the low-level situation. Manipulating by video track, we observed an anxiety-like behavior including high speed and abnormal photoperiod accommodation after exposure to fipronil at environmental typical dose in zebrafish larvae. Examining the unbiased metabolomic profiles, we found perturbation in several metabolic pathways, including the increased contents of fatty acids and glycerol and the decreased levels of the glycine, serine, and branched amino acid. We presumed that observed enhanced fatty acid utility was in response to increase energy demands caused by anxiety like behavior. Additionally, the body burden of neurotransmitter such as glycine and L-glutamate may concurrently stimulate the swimming behavior. The insight of this study showed that integral perturbation such as metabolism helps us to further understand the risk to aquatic fish at the environmentally relevant levels.

Growth-promoting effects of sustained swimming in fingerlings of gilthead sea bream (Sparus aurata L.)

Fish growth is strongly influenced by environmental and nutritional factors and changing culture conditions can help optimize it. The importance of early-life experience on the muscle phenotype later in life is well known. Here, we study the effects of 5 weeks of moderate and sustained swimming activity (5 BL s(-1)) in gilthead sea bream during early development. We analysed growth and body indexes, plasma IGF-I and GH levels, feed conversion, composition [proximate and isotopic ((15)N/(13)C)] and metabolic key enzymes (COX, CS, LDH, HOAD, HK, ALAT, ASAT) of white muscle. Moderate and continuous exercise in fingerlings of gilthead sea bream increased plasma IGF-I, whereas it reduced plasma GH. Under these conditions, growth rate improved without any modification to feed intake through an increase in muscle mass and a reduction in mesenteric fat deposits. There were no changes in the content and turnover of muscle proteins and lipid reserves. Glycogen stores were maintained, but glycogen turnover was higher in white muscle of exercised fish. A lower LDH/CS ratio demonstrated an improvement in the aerobic capacity of white muscle, while a reduction in the COX/CS ratio possibly indicated a functional adaptation of mitochondria to adjust to the tissue-specific energy demand and metabolic fuel availability in exercised fish. We discuss the synergistic effects of dietary nutrients and sustained exercise on the different mitochondrial responses.

Unraveling the molecular signatures of oxidative phosphorylation to cope with the nutritionally changing metabolic capabilities of liver and muscle tissues in farmed fish

Mitochondrial oxidative phosphorylation provides over 90% of the energy produced by aerobic organisms, therefore the regulation of mitochondrial activity is a major issue for coping with the changing environment and energy needs. In fish, there is a large body of evidence of adaptive changes in enzymatic activities of the OXPHOS pathway, but less is known at the transcriptional level and the first aim of the present study was to define the molecular identity of the actively transcribed subunits of the mitochondrial respiratory chain of a livestock animal, using gilthead sea bream as a model of farmed fish with a high added value for European aquaculture. Extensive BLAST searches in our transcriptomic database (www.nutrigroup-iats.org/seabreamdb) yielded 97 new sequences with a high coverage of catalytic, regulatory and assembly factors of Complex I to V. This was the basis for the development of a PCR array for the simultaneous profiling of 88 selected genes. This new genomic resource allowed the differential gene expression of liver and muscle tissues in a model of 10 fasting days. A consistent down-regulated response involving 72 genes was made by the liver, whereas an up-regulated response with 29 and 10 differentially expressed genes was found in white skeletal muscle and heart, respectively. This differential regulation was mostly mediated by nuclear-encoded genes (skeletal muscle) or both mitochondrial- and nuclear-encoded genes (liver, heart), which is indicative of a complex and differential regulation of mitochondrial and nuclear genomes, according to the changes in the lipogenic activity of liver and the oxidative capacity of glycolytic and highly oxidative muscle tissues. These insights contribute to the identification of the most responsive elements of OXPHOS in each tissue, which is of relevance for the appropriate gene targeting of nutritional and/or environmental metabolic disturbances in livestock animals.

Effects of exercise training on carbohydrate and lipid catabolism in the swimming muscles of Nile tilapia (Oreochromis niloticus)

This study aims to determine the effects of exercise training on carbohydrate and lipid catabolism in the swimming muscles of Nile tilapia (Oreochromis niloticus) by measuring the levels of related enzymes, lipids and free fatty acids. We designed one control group and two training groups of fish that were exercised at different training intensities [0, 1 and 1.5 body lengths per second (bl/s)]. The fish in the experimental groups were trained for 12 h/day for 4 weeks. Compared with the control group, the 1 and 1.5 bl/s groups showed significantly increased hexokinase and pyruvate kinase activities in red muscle (p < 0.05). In white muscle, pyruvate kinase activity was significantly higher in the 1.5 bl/s group than in the control group (p < 0.05), and hexokinase activity did not significantly differ between the groups. The activities of hormone-sensitive lipase and carnitine palmitoyltransferase I in both muscle types were significantly lower in the training groups than in the control group (p < 0.05). The plasma-free fatty acid level decreased (p < 0.05), while the lipid percentages increased in red muscle (p < 0.05) after exercise training. These findings clearly indicated that with exercise training, glycolysis increased and lipid oxidation decreased in the swimming muscle of tilapia.

New insights into fish swimming: a proteomic and isotopic approach in gilthead sea bream

Moderate exercise enhances fish growth, although underlying physiological mechanisms are not fully known. Here we performed a proteomic and metabolic study in white (WM) and red (RM) muscle of gilthead sea bream juveniles swimming at 1.5 body lengths per second. Continuous swimming for four weeks enhanced fish growth without increasing food intake. Exercise affected muscle energy stores by decreasing lipid and glycogen contents in WM and RM, respectively. Protein synthesis capacity (RNA/protein), energy use (estimated by lipid-δ(13)C and glycogen-δ(13)C), and enzymatic aerobic capacity increased in WM, while protein turnover (expressed by δ(15)N-fractionation) did not change. RM showed no changes in any of these parameters. 2D-PAGE analysis showed that almost 15% of sarcoplasmic protein spots from WM and RM differed in response to exercise, most being over-expressed in WM and under-expressed in RM. Protein identification by MALDI-TOF/TOF-MS and LC-MS/MS revealed exercise-induced enhancement of several pathways in WM (carbohydrate catabolism, protein synthesis, muscle contraction, and detoxification) and under-expression of others in RM (energy production, muscle contraction, and homeostatic processes). The mechanism underpinning the phenotypic response to exercise sheds light on the adaptive processes of fish muscles, being the sustained-moderate swimming induced in gilthead sea bream achieved mainly by WM, thus reducing the work load of RM and improving swimming performance and food conversion efficiency.

Feed restriction up-regulates uncoupling protein 3 (UCP3) gene expression in heart and red muscle tissues of gilthead sea bream (Sparus aurata L.) New insights in substrate oxidation and energy expenditure

The physiological regulation of the mitochondrial uncoupling protein 3 (UCP3) remains practically unexplored in fish and the aim of this study was to examine the effects of ration size on the regulation of UCP3 in heart, red skeletal muscle and white skeletal muscle of gilthead sea bream (Sparus aurata L.). Juvenile fish were fed at three different levels for 11 weeks: i) full ration until visual satiety (R(100) group), ii) 70% of satiation (R(70) group) and iii) 70% of satiation with two finishing weeks at the maintenance ration (20% of the satiation level) (R(70-20) group). The thirty percent feed restriction improved fish performance, increasing feed conversion efficiency and circulating levels of insulin-like growth factor-I (IGF-I). Fish of the R(70-20) group showed reduced growth and low circulating levels of IGF-I in combination with increased circulating concentrations of growth hormone and free fatty acids. Feed restriction did not alter UCP3 transcript levels in white skeletal muscle, but improved this tissue's oxidative capacity as assessed by changes in glycolytic and oxidative mitochondrial enzyme activities. In contrast, in cardiac and red skeletal muscle tissues, this dietary treatment primarily increased UCP3 mRNA expression. The respiratory control ratio of freshly isolated heart mitochondria was slightly lower in R(70-20) fish than in R(100) fish, which suggests that there was an increase in mitochondrial uncoupling concomitant with the enhanced UCP3 mRNA expression. Altogether, these findings highlight the different adaptive mechanism of glycolytic and highly oxidative muscle tissues for their rapid adjustment to varying feed intake.