Metabolism in Fish During Exercise

Functional Feeds to Tackle Meagre (Argyrosomus regius) Stress: Physiological Responses under Acute Stressful Handling Conditions

Marine algae are recognised sources of bioactive compounds that have attracted great interest as nutritional supplements for aquaculture fish. Intensive rearing conditions often expose fish to husbandry-related stressors, rendering fish more susceptible to disease and reducing production yields. The present work evaluated the potential of two marine algae extracts (Fucus vesiculosus and Nannochloropsis gaditana) as nutritional supplements to mitigate stress effects in meagre (Argyrosomus regius) exposed to an acute handling stress (AS). A plant-based diet was used as a control, and three other diets were prepared, which were similar to the control diet but supplemented with 1% of each algal extract or a combination of the two extracts (0.5% each). The effects of supplemented diets on stress biomarkers, antioxidant enzyme activities, and immune response were analysed in fish exposed to AS after 4 weeks of feeding. Supplemented diets did not affect growth performance but the inclusion of F. vesiculosus promoted higher feed efficiency, as compared to the control group. Dietary algal extracts supplementation reduced plasma glucose levels, increased white blood cell counts, and reduced the expression of pro-inflammatory genes when compared with the control. N. gaditana supplementation led to a reduction in hepatic antioxidant enzyme activity and glutathione levels, while F. vesiculosus supplementation increased muscle glutathione reductase activity and reduced lipid peroxidation. These findings support the potential of algal extracts as nutraceuticals in aquafeeds to enhance the ability of fish to cope with husbandry-related stressful conditions and ultimately improve fish health and welfare.

Growth and Metabolic Response of Chinese Perch to Different Dietary Protein-to-Energy Ratios in Artificial Diets

The effect of dietary nutrients on novel farm species has always garnered wide research and economic interest. Chinese perch, an economically important carnivorous fish, accepts an artificial diet after taming, so it is essential to evaluate and optimize the nutritional and metabolic demands of this species. However, little is known about the effect of an artificial diet on the growth and metabolism of Chinese perch. Therefore, the present study evaluated the growth and metabolic responses of Chinese perch to experimental diets with different dietary protein/energy (P/E) ratios. Five isoenergetic diets (18 kJ/g) with graded levels of P/E ratios of 30.58, 33.22, 35.90, 38.6, and 41.35 mg/kJ (named A, B, C, D, and E) were formulated. A total of 225 Chinese perch (64.89 ± 0.28 g) were divided into five groups (triplicate tanks for each group), distributed into 15 (350 L) fiberglass tanks, and fed twice a day at 4% of fish wet body weight with the respective P/E ratio diets for 10 weeks. Compared with the other groups, Chinese perch in Group C showed significantly improved growth performance, weight gain (WG), specific growth rate (SGR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF), feed utilization, feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE), energy retention efficiency (ERE), and feed efficiency (FE) as well as whole-body, muscle, and liver composition. Chinese perch in Group A, on the other hand, had the lowest growth performance, feed utilization, and body composition compared with the other groups. The activities of nitrogen metabolism-related enzymes (alanine aminotransferase (ALT), aspartate aminotransferase (AST) glutamate dehydrogenase (GDH), and adenosine 5′-monophosphate deaminase (AMPD)) as well as the mRNA expression of the GDH and AMPD genes were significantly lower than those in the other groups. Similarly, the expression of NPY and AgRp were significantly higher in Group C compared with the other groups. However, the gene expression of CART and POMC was not affected by the dietary P/E ratios. In Group A, the expression of mTOR, S6K, and 4EBP1 was significantly lower and that of AMPK, LKB1, and eEF2 was significantly higher when compared with the other groups. Biochemical analysis of blood showed that ALT, AST, total protein (TP), alkaline phosphatase (ALP), glucose (GLU), blood urea nitrogen (BUN), and triglyceride (TG) levels were also affected by the dietary P/E ratio. From our results, we concluded that Chinese perch growth performance and nutrient metabolism were significantly affected by the P/E ratio of the artificial diet. Second-order polynomial regression analysis revealed that Chinese perch growth performance was optimal at a P/E ratio of 37.98 in the artificial diet.

Study of sodium arsenite induced biochemical changes on certain biomolecules of the freshwater catfish Clarias batrachus

Toxic impact of sublethal concentration (1 mg/L; 5% of 96h LC50 value) of sodium arsenite (NaAsO2) on certain biomolecules (proteins, nucleic acids, lipids, and glycogen) of five tissue components (muscles, liver, brain, skin, and gills) of the freshwater catfish Clarias batrachus was analysed. The important toxic manifestations include marked decrease in the concentration of proteins (21.72-45.42% in muscles; 3.42-53.94% in liver; 15.39-45.42% in brain; 15.40-4.00% in skin and 11.35-64.13% in gills), DNA (0.55-22.95% in muscles; 8.33-14.06% in liver; 5.30-18.40% in brain; 13.57-52.80% in skin; and 12.38-31.01% in gills), RNA (42.68-76.16% in muscles; 10.68-39.75% in liver; 5.66-29.05% in brain; 7.72-27.93% in skin and 21.47-44.38% in gills) and glycogen (24.00-51.72% in muscles; 49.11-72.45% in liver; 11.49-26.03% in brain; 26.13-38.05% in skin and 17.80-37.97% in gills). Excepting liver where the lipid content increases (15.82-24.13%), the fat content also showed depletion in their concentration (10.40-29.83% in muscles; 8.30-34.45% in brain; 8.94-31.47% in skin and 12.75-28.86% in gills), in the rest of the organ systems.

The physiological response to anthropogenic stressors in marine elasmobranch fishes: a review with a focus on the secondary response

Elasmobranchs (sharks, rays, and skates) are currently facing substantial anthropogenic threats, which expose them to acute and chronic stressors that may exceed in severity and/or duration those typically imposed by natural events. To date, the number of directed studies on the response of elasmobranch fishes to acute and chronic stress are greatly exceeded by those related to teleosts. Of the limited number of studies conducted to date, most have centered on sharks; batoids are poorly represented. Like teleosts, sharks exhibit primary and secondary responses to stress that are manifested in their blood biochemistry. The former is characterized by immediate and profound increases in circulating catecholamines and corticosteroids, which are thought to mobilize energy reserves and maintain oxygen supply and osmotic balance. Mediated by these primary responses, the secondary effects of stress in elasmobranchs include hyperglycemia, acidemia resulting from metabolic and respiratory acidoses, and profound disturbances to ionic, osmotic, and fluid volume homeostasis. The nature and magnitude of these secondary effects are species-specific and may be tightly linked to metabolic scope and thermal physiology as well as the type and duration of the stressor. In fishes, acute and chronic stressors can incite a tertiary response, which involves physiological changes at the organismal level, thereby impacting growth rates, reproductive outputs or investments, and disease resistance. Virtually no studies to date have been conducted on the tertiary stress response in elasmobranchs. Given the diversity of elasmobranchs, additional studies that characterize the nature, magnitude, and consequences of physiological stress over a broad spectrum of stressors are essential for the development of conservation measures. Additional studies on the primary, secondary, and tertiary stress response in elasmobranchs are warranted, with particular emphasis on expanding the range of species and stressors examined. Future studies should move beyond simply studying the effects of known stressors and focus on the underlying physiological mechanisms. Such studies should include the coupling of stress indicators with quantifiable aspects of the stressor, which will allow researchers to test hypotheses on survivorship and, ultimately, derive models that effectively link physiology to mortality. Studies of this nature are essential for decision-making that will result in the effective management and conservation of these species.

Effects of dietary levels of protein on nitrogenous metabolism of Rhamdia quelen (Teleostei: Pimelodidae)

This manuscript reports changes in key enzymes and metabolites related to protein metabolism and nitrogen excretion in the liver of juveniles jundiá (Rhamdia quelen) fed on isocaloric diets containing 20%, 27%, 34% and 41% of crude protein. The hepatic activity of alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), glutamate dehydrogenase (GDH), and arginase (ARG) increased with the content of protein in the diet, and the ratios among the aminotransferases and GDH allowed evaluating metabolic preference. The concentration of free amino acids, ammonia and urea also rose with the dietary protein content. Increase of plasma urea and ammonia was the resultant effect of over amino acids catabolism as consequence of dietary protein surplus. Since the increase of protein in the diets resulted in weight gain, the rise in the hepatic activity of protein-metabolising enzymes in the fish fed high protein diets denoted effective use of dietary amino acids for growth and as a substrate for gluconeogenesis. Analysis of changes on metabolite levels and key enzyme activities in amino acid metabolism is proposed as a tool for assessing the proper balance of diet macronutrients.

Influence of seasonal temperature on the repeat swimming performance of rainbow trout Oncorhynchus mykiss

While the temperature dependence of exercise performance in fishes is reasonably well documented, information on the temperature dependence of metabolic recovery and reperformance is scant. This study examined the recovery of swimming performance after exhaustive exercise in rainbow trout Oncorhynchus mykiss at seasonal temperatures ranging from 5 to 17 degrees C and explored the relationship between performance and preceding metabolic state. The primary objective of the study was to test the hypothesis that increased temperature increases the capability of rainbow trout to repeat a critical swimming speed (U(crit)), as assessed by two consecutive critical swimming speed tests separated by a 40 min rest interval. An additional expectation was that certain plasma ionic, metabolic and humoral parameters would be correlated with how well fish reperformed and so plasma levels of lactate, potassium, ammonia, osmolality, sodium and cortisol, as well as hematocrit, were monitored before, during and after the swim challenges via an indwelling cannula in the dorsal aorta. As expected, performance in the first U(crit) test (U(crit1)) was positively related to temperature. However, the relationship between U(crit1) and reperformance (U(crit2)) was not dependent on acclimation temperature in a simple manner. Contrary to our expectations, U(crit2) was less than U(crit1) for warm-acclimated fish (14.9+/-1.0 degrees C), whereas U(crit2) equaled U(crit1) for cold-acclimated fish (8.4+/-0.9 degrees C). Cold-acclimated fish also exhibited a lower U(crit1) and less metabolic disruption compared with warm-acclimated fish. Thus, while warm acclimation conferred a faster U(crit1), a similar swimming speed could not be attained on subsequent swim after a 40 min recovery period. This finding does not support the hypothesis that the ability of rainbow trout to reperform on U(crit) test is improved with temperature. Both plasma lactate and plasma potassium levels were strongly correlated with U(crit1) performance. Therefore, the higher U(crit1) of warm-acclimated fish may have been due in part to a greater anaerobic swimming effort compared with cold-acclimated fish. In fact, a significant correlation existed between the plasma lactate concentration prior to the start of the second test and the subsequent U(crit2) performance, such that U(crit2) decreased when a threshold plasma lactate level of around 12.2 mmol l(-1) was surpassed for the initial swim. No other measured plasma variable showed a significant relationship with the U(crit2) performance. We conclude that warm-acclimated fish, by apparently swimming harder and possibly more anaerobically compared with cold-acclimated fish, were unable to recovery sufficiently well during the fixed recovery period to repeat this initial level of performance, and this poorer repeat performance was correlated with elevations in plasma lactate levels.

Physiological basis of temperature-dependent biogeography: trade-offs in muscle design and performance in polar ectotherms

Polar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae).

In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein,thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid—base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.

Responses to prolonged hypoxia by rainbow trout (Salmo gairdneri) I. Free amino acids and proteins in plasma, liver and white muscle

In order to estimate the mobilization of nitrogen compounds for energetic purposes in trout under hypoxic conditions, commercial-size rainbow trout, acclimated to 15°C, were maintained for 10 weeks at an oxygen level of 5.3 ± 0.5 mg/l ('hypoxic' group) or 8.4 ± 0.4 mg/I (control group), and the changes in tissue concentrations of free amino acids and proteins studied. In animals subjected to hypoxia, there was a decrease in plasma free amino acids involved in gluconeogenesis, liver alanine and aspartic acid, plasma and liver protein concentrations, and muscle free histidine. These results suggest a trend of rainbow trout metabolic activity towards energy production at the expense of anabolism when oxygen availability in water is limited over a long period of time.

Ammonia distribution and excretion in fish

This paper reviews the literature concerning ammonia production, storage and excretion in fish. Ammonia is the end product of protein catabolism and is stored in the body of fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted. Like other weak acids and bases, ammonia is distributed between tissue compartments in relation to transmembrane pH gradients. NH3 is generally equilibrated between compartments but NH4 (+) is distributed according to pH. Ammonia is eliminated from the blood upon passage through the gills. The mechanisms of branchial ammonia excretion vary between different species of fish and different environments, and primarily involves NH3 passive diffusion and NH4 (+)/Na(+) exchange. Water chemistry near the gill surface may also be important to ammonia excretion, but a more accurate measurement of the NH3 gradient across the gill epithelium is required before a more detailed analysis of NH3 and NH4 (+) excretion can be made.

Amino acid utilisation in isolated hepatocytes from rainbow trout

The utilisation (conversion to CO2 and/or glucose) of a series of amino acids by isolated trout hepatocytes was investigated and compared to the utilisation of lactate and palmitate. In fed fish, several amino acids (alanine, serine, asparagine and glycine) and lactate produced CO2 at considerably higher rates than palmitate. During starvation plus exercise, the rate of CO2 production from palmitate increased while that from lactate and most of the amino acids decreased. Gluconeogenesis from amino acids in fed fish was lower than from lactate. Serine and asparagine were the most effective substrates; alanine gave lower rates of incorporation. During prolonged starvation plus exercise, the rates of gluconeogenesis from amino acids increased twofold and, simultaneously, there was a corresponding increase in phosphoenolpyruvate carboxykinase activity in liver. It is concluded that several amino acids (dietary or released from muscle protein) are potentially major oxidative substrates in trout. In addition, amino acids appear to have the capability to maintain supplies of glucose during a period of prolonged starvation and exercise. No evidence could be found to support the contention that alanine is the most important glucogenic amino acid.