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Nitrite is usual in water of intensive rearing systems. Considering its oxidative harmful potential, it was selected to challenge matrinxa Brycon amazonicus reared in sustained swimming (SS) (with flowing water adjusted to speed at 1.0 BL seg−1 (long-duration aerobic metabolic characteristic) and evaluate any beneficial effect of such rearing system to enhance the fish potential to cope with this oxidant stressor in fish farmings. Some parameters of oxidative stress, intermediary metabolism and hematometry were measured in matrinxa adapted to SS and exposed to the highest environmental nitrite concentration allowed by law. The experiments were performed in two steps. At first, fish were adapted to exercise under SS for 90 days. Subsequently, adapted fish were exposed to environmental nitrite (1.0 mg L−1) for 24 h in order to evaluate their physiological responses. The results were compared with fish let in the same environment but from motionless water. Glycogen, glucose, pyruvate, lactate, free amino acids and ammonia were quantified in liver, plasma and muscle. Lipid peroxidation (LPO), glutathione peroxidase (GPx) and catalase (CAT) were assayed in liver and white muscle. Hematometry data were obtained using standard procedures. Sustained swimming practice enhance the hematological capacity of fish, improving oxidative metabolic responses; changing the ability to mobilize carbohydrates for energy purposes; facilitating the energy-dependent detoxification process; and minimizing the mobilization of amino acids for this purpose. In conclusion, the potential of matrinxa adapted to SS to cope with oxidative stress caused by environmental nitrite was enhanced. [ABSTRACT FROM AUTHOR]

Simple Summary: Based on the results of swimming tests in groups of fingerling sea bass, we selected an appropriate speed of 1.5 BLs−1 to apply to sea bass farming; it represents 1/3 of their maximum aerobic speed. Sea bass fingerlings maintained for 6 weeks at this velocity do not impair their growth nor modify the composition of red and white muscle, but they expand their aerobic capacity and show several metabolic changes, especially in white muscle, related to the improvement of their use of nutrients. At the end, fish acquired a more-aerobic phenotype, which leads to greater robustness of the individuals, therefore, increasing their resistance capacity in a wide range of environments without compromising production. 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. [ABSTRACT FROM AUTHOR]

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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.

A trend in large yellow croaker (Larimichthys crocea) aquaculture is to establish production sites suitable for extreme weather conditions. However, continuous and strong currents can harm fish welfare. To determine a suitable site location, the swimming ability of large yellow croakers must be assessed. This study aims to provide novel insights into the physiological characteristics of large yellow croaker swimming and a reference for fishing and cage site selection. Currently, research on large yellow croakers has focused on behavior analysis. Herein, we investigate the effects of swimming on large yellow croakers' metabolites by examining the preferred speed of the group and the sustained swimming ability of single-tailed fish. We evaluated factors that influence the large yellow croaker's swimming fatigue by quantifying the metabolite contents and constructing a sustained swimming model. The results showed that large yellow croaker populations tend to grow in low-velocity environments, similar to their traditional habitat. The samples were taken at different swimming times at a flow velocity of 0.35 m/s. According to the results of the metabolite content analysis, blood glucose levels are closely associated with the swimming ability in large yellow croakers. The content of liver glycogen, which regulates blood glucose concentration, decreased in a certain linear relationship. The sustained swimming model of the large yellow croaker was constructed according to the changes in liver glycogen content. Based on our findings, we recommend the following: (1) for large yellow croakers with a size of approximately 13.5 cm (approximately 1 year old), the water velocity inside the cage should not exceed 2.6 BL/s; (2) the concentration of liver glycogen limits the sustained swimming ability of the large yellow croaker, providing a reference for studying the swimming ability of other fish. [ABSTRACT FROM AUTHOR]

Nitrite is usual in water of intensive rearing systems. Considering its oxidative harmful potential, it was selected to challenge matrinxa Brycon amazonicus reared in sustained swimming (SS) (with flowing water adjusted to speed at 1.0 BL seg -1 (long-duration aerobic metabolic characteristic) and evaluate any beneficial effect of such rearing system to enhance the fish potential to cope with this oxidant stressor in fish farmings. Some parameters of oxidative stress, intermediary metabolism and hematometry were measured in matrinxa adapted to SS and exposed to the highest environmental nitrite concentration allowed by law. The experiments were performed in two steps. At first, fish were adapted to exercise under SS for 90 days. Subsequently, adapted fish were exposed to environmental nitrite (1.0 mg L -1 ) for 24 h in order to evaluate their physiological responses. The results were compared with fish let in the same environment but from motionless water. Glycogen, glucose, pyruvate, lactate, free amino acids and ammonia were quantified in liver, plasma and muscle. Lipid peroxidation (LPO), glutathione peroxidase (GPx) and catalase (CAT) were assayed in liver and white muscle. Hematometry data were obtained using standard procedures. Sustained swimming practice enhance the hematological capacity of fish, improving oxidative metabolic responses; changing the ability to mobilize carbohydrates for energy purposes; facilitating the energy-dependent detoxification process; and minimizing the mobilization of amino acids for this purpose. In conclusion, the potential of matrinxa adapted to SS to cope with oxidative stress caused by environmental nitrite was enhanced., Competing Interests: Declarations. Ethical approval: Approved by the Ethics Committee on the use of Animals (CEUA) of the Federal University of Grande Dourados (protocol #39/2016, CEUA/UFGD). Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

A trend in large yellow croaker (Larimichthys crocea) aquaculture is to establish production sites suitable for extreme weather conditions. However, continuous and strong currents can harm fish welfare. To determine a suitable site location, the swimming ability of large yellow croakers must be assessed. This study aims to provide novel insights into the physiological characteristics of large yellow croaker swimming and a reference for fishing and cage site selection. Currently, research on large yellow croakers has focused on behavior analysis. Herein, we investigate the effects of swimming on large yellow croakers’ metabolites by examining the preferred speed of the group and the sustained swimming ability of single-tailed fish. We evaluated factors that influence the large yellow croaker’s swimming fatigue by quantifying the metabolite contents and constructing a sustained swimming model. The results showed that large yellow croaker populations tend to grow in low-velocity environments, similar to their traditional habitat. The samples were taken at different swimming times at a flow velocity of 0.35 m/s. According to the results of the metabolite content analysis, blood glucose levels are closely associated with the swimming ability in large yellow croakers. The content of liver glycogen, which regulates blood glucose concentration, decreased in a certain linear relationship. The sustained swimming model of the large yellow croaker was constructed according to the changes in liver glycogen content. Based on our findings, we recommend the following: (1) for large yellow croakers with a size of approximately 13.5 cm (approximately 1 year old), the water velocity inside the cage should not exceed 2.6 BL/s; (2) the concentration of liver glycogen limits the sustained swimming ability of the large yellow croaker, providing a reference for studying the swimming ability of other fish.

Zebrafish are increasingly used as a vertebrate model organism for various traits including swimming performance, obesity and metabolism, necessitating high-throughput protocols to generate standardized phenotypic information. Here, we propose a novel and cost-effective method for exercising zebrafish, using a coffee plunger and magnetic stirrer. To demonstrate the use of this method, we conducted a pilot experiment to show that this simple system provides repeatable estimates of maximal swim performance (intra-class correlation [ICC] = 0.34–0.41) and observe that exercise training of zebrafish on this system significantly increases their maximum swimming speed. We propose this high-throughput and reproducible system as an alternative to traditional linear chamber systems for exercising zebrafish and similarly sized fishes.

Zebrafish are increasingly used as a vertebrate model organism for various traits includ- ing swimming performance, obesity and metabolism, necessitating high-throughput protocols to generate standardized phenotypic information. Here, we propose a novel and cost-effective method for exercising zebrafish, using a coffee plunger and magnetic stirrer. To demonstrate the use of this method, we conducted a pilot experiment to show that this simple system provides repeatable estimates of maximal swim performance (intra-class correlation [ICC] = 0.34-0.41) and observe that exercise training of zebrafish on this system significantly increases their maximum swimming speed. We propose this high-throughput and reproducible system as an alternative to traditional linear chamber systems for exercising zebrafish and similarly sized fishes. [ABSTRACT FROM AUTHOR]

Shrimp locomotion includes walking, swimming, and tail-flipping, all essential for survival. Understanding the pathway and use of energy during different modes of locomotion is important in understanding the strategy and evolution of locomotion. We explored the mechanisms of energy supply during swimming and tail-flipping locomotion modes in the whiteleg shrimp Litopenaeus vannamei (Boone, 1931). We studied the metabolic pathways of glycogen and triglycerides and the regulation of glycolytic enzyme on glycolysis, and analyzed their relationship with the behavior modes of locomotion. Swimming includes sustained and prolonged modes, where the shrimp were forced to swim at a speed of 10 cm s-1 for 200 min (sustained), and at 20 cm s-1 until fatigue (prolonged). In tail-flipping locomotion, shrimp were forced to tail-flip by tapping the animal until fatigue. The results showed that the hydrolysis of glycogen in pleopod muscle increased with the rate of pleopod strokes due to increased energy demand during fast swimming. Similarly, glycogen breakdown in abdominal muscles was increased during tail-flipping. Glycogen and triglycerides were utilized in aerobic metabolism pathway as a result of the lower rate of pleopod strokes during sustained swimming. Prolonged and tail-flipping modes of locomotion were powered by anaerobic glycolysis because oxygen supply probably was not sufficient to meet the requirements of glycogen and triglyceride oxidation. Lactate accumulation due to increased glycolysis consequently resulted in locomotion fatigue. These findings highlight our understanding of physiology and behavior of locomotion in shrimps, essential during migration, foraging, and escape from predators. [ABSTRACT FROM AUTHOR]

Deleterious changes in metabolism, growth performance and body composition may be observed if fish are constrained to swimming continuously or intermittently at over-speeds. This study evaluates effects of four water speeds on growth, body composition and hematologic profile of juvenile matrinxã, Brycon amazonicus. Fish (33.3 ± 0.9 g and 13.44 ± 0.1 cm) were held for 90 days in five water speeds (0.0 - control, 1.0, 1.5, 2.0 and 2.5 body lengths per second - BLAt swimming speeds ranging on 1.0 and 1.5 BL s–1, in fish growth was 20% higher. Hemoglobin and red blood cells at 1.5 BL s–1 increased 24% and 18% respectively; hematocrit was 17% higher in all exercised fish; protein content of white muscle at 1.0 BL s–1 was 2% higher; lipid deposition in red muscle at 1.0 BL s–1 was 22% higher and water retention 3% lower. Crude energy levels enhanced 10% in all exercised fish; liver water retention was 6% lower at 1.0 BL s–1; liver lipid composition was 29% higher than control and 34% higher than 1.5 BL s–1; liver crude energy increased at 1.0 BL s–1 as compared with control and 2.5 BL s–1. Lipid deposition in ventral muscle was 9% higher at 2.0 BL s–1. Although high lipid deposition of matrinxã has been achieved in moderate swimming speeds, lipids may be the main fuel source to maintain the metabolic demands of exercised matrinxã. The best water flow speed for optimized growth of matrinxã ranged on 1.0 and 1.5 BL s–1.Modificações deletérias no metabolismo, rendimento de crescimento e composição corporal podem ser observadas em peixes forçados à natação contínua ou intermitente sob velocidades excessivas. Neste trabalho, os efeitos de quatro velocidades de água no crescimento, composição corporal e perfil hematológico foram avaliados em matrinxãs juvenis, Brycon amazonicus. Os peixes (33,3 ± 0,9 g e 13,44 ± 0,1 cm) foram mantidos durante 90 dias em cinco velocidades de água (0,0 – controle; 1,0; 1,5; 2,0 e 2,5 comprimentos corporais - BL por segundo). As melhores velocidades de nadado estiveram entre 1,0 e 1,5 BL s–1, nas quais o crescimento dos peixes foi 20% maior que nas outras. A hemoglobina e as células vermelhas do sangue em 1,5 BL s–1 aumentaram 24% e 18% respectivamente; o hematócrito foi 17 % maior em todos os peixes exercitados; o conteúdo de proteína do músculo branco em 1,0 BL s–1 foi 2% maior; a deposição de lipídio no músculo vermelho em 1,0 BL s–1 foi 22% maior e a retenção de água foi 3% menor. Os níveis de energia bruta aumentaram 10% em todos os peixes exercitados; a retenção de água no fígado foi 6 % menor em 1,0 BL s–1; a composição de lipídio no fígado foi 29% maior do que o controle e 34% maior do que a 1,5 BL s–1; a energia bruta no fígado aumentou em 1.0 BL s–1 comparada com o controle e 2,5 BL s–1. A deposição de lipídio no músculo ventral foi 9% maior em 2,0 BL s–1. Embora alta deposição de lipídio em matrinxã tenha sido obtida em velocidades moderadas de nado, os lipídios podem ser a fonte de combustível principal para manter as exigências metabólicas de matrinxã em exercício. A melhor velocidade de nado para obter o melhor crescimento em matrinxã está entre 1,0 e 1,5 BL s–1.

Background: determination of water velocity for optimum fish growth is fundamental since its duration and intensity can interfere with the metabolic preference for some biochemical paths, resulting in the use of specific substrates for fish growth. Objective: the purpose of this study was to assess the metabolic adjustments of juvenile matrinxã (Brycon amazonicus) reared under various sustained swimming conditions (SS). Methods: fish were subjected to SS for 90 days at five swimming speeds: 0.0 (control), 1.0, 1.5, 2.0, and 2.5 Body Length per second (BL/s). At the end of the experimental period, fish were euthanized; samples of blood, liver, white-muscle, red-muscle and ventral muscle were collected and metabolite concentrations were evaluated. Results: fish reared between 1.0-1.5 BL/s increased the hepatosomatic index (HSI) while those swimming at velocities higher than 1.5 BL/s showed diminished HSI and visceral fat. Fish under moderate swimming utilized visceral fat to supply energy for red muscle contractions while white muscle of fish swimming at higher speeds used carbon backbones from amino acids plus visceral fat. Conclusion: sustained swimming between 1.0-1.5 BL/s enhanced the intermediary metabolism of B. amazonicus, improving fish performance. Future studies linking macronutrient dietary levels and SS should allow adjusting rearing conditions under SS to optimize growth versus metabolic performance. [ABSTRACT FROM AUTHOR]

Phalarodon atavus from the Germanic Muschelkalk Basin was previously represented only by cranial elements. Here we report a nearly complete and articulated specimen of P. atavus from the Middle Triassic Luoping Biota, Yunnan, South China. This is the first specimen of P. atavus from outside the Germanic Basin. This discovery demonstrates a peri- Tethyan distribution of P. atavus. The new specimen is also the first one preserving the postcranial anatomy of this species, providing the opportunity to evaluate its sustained swimming ability. Inferences made on its functional morphology suggest that this species was probably adapted for active foraging. Tooth crown morphology suggests that P. atavus may have preferred externally soft prey. [ABSTRACT FROM AUTHOR]

Here we examined the use of stable isotopes, [13C]starch and [15N]protein, as dietary tracers to study carbohydrate assimilation and distribution and protein utilisation, respectively, by rainbow trout (Oncorhynchus mykiss). The capacity of glucose uptake and use by tissues was studied, first, by varying the digestibility of carbohydrate-rich diets (30 % carbohydrate), using raw starch and gelatinised starch (GS) and, second, by observing the effects of two regimens of activity (voluntary swimming, control; sustained swimming at 1·3 body lengths/s, exercise) on the GS diet. Isotopic ratio enrichment (13C and 15N) of the various tissue components (protein, lipid and glycogen) was measured in the liver, muscles, viscera and the rest of the fish at 11 and 24 h after a forced meal. A level of 30 % of digestible carbohydrates in the food exceeded the capacity of rainbow trout to use this nutrient, causing long-lasting hyperglycaemia that raises glucose uptake by tissues, and the synthesis of glycogen and lipid in liver. Total 13C recovered 24 h post-feeding in the GS group was lower than at 11 h, indicating a proportional increase in glucose oxidation, although the deposition of lipids in white muscle (WM) increased. Prolonged hyperglycaemia was prevented by exercise, since sustained swimming enhances the use of dietary carbohydrates, mainly through conversion to lipids in liver and oxidation in muscles, especially in red muscle (RM). Higher recoveries of total 15N for exercised fish at 24 h, mainly into the protein fraction of both RM and WM, provide evidence that sustained swimming improves protein deposition, resulting in an enhancement of the protein-sparing effect. [ABSTRACT FROM PUBLISHER]

Fish endurance swimming is primarily powered by lipids supplied to red muscle by the circulation, but the mechanism of delivery remains unknown. By analogy to mammals, previous studies have focused on non-esterified fatty acids (NEFA bound to albumin), but lipoproteins have not been considered as an energy shuttle to working muscles. The effects of exercise on fish lipoprotein lipase (LPL) have never been investigated. We hypothesized that LPL and circulating lipoproteins would be modified by prolonged swimming. Because LPL is naturally bound to the endothelium, we have used heparin to release the enzyme in the circulation and to characterize reserve capacity for lipoprotein catabolism. The effects of exercise (4 days at 1.5 body lengths s-1 in a swim tunnel) were measured for red muscle LPL, post-heparin plasma LPL, and lipoprotein concentration/composition. Red muscle LPL activity increased from 18±5 (rest) to 49± 9 nmol fatty acids min-1 g-1 (swimming). In resting fish, heparin administration caused a 27-fold increase in plasma LPL activity that reached a maximum of 1.32± 0.67 p mo1 fatty acids min1 mt1 plasma. This heparin- induced response of plasma LPL was not different between resting controls and exercised fish. Heparin or prolonged swimming had no effect on the concentration/composition of lipoproteins that contain 92% of the energy in total plasma lipids. We conclude that (1) red muscle LPL is strongly activated by endurance swimming, (2) rainbow trout have a high reserve capacity for hydrolyzing lipoproteins, and (3) future studies should aim to measure lipoprotein flux because their concentration does not reflect changes in flux. These novel characteristics of fish LPL imply that lipoproteins are used as a metabolic shuttle between fat reserves and working muscles, a strategy exploiting an abundant source of energy in rainbow trout. 0.67 μmol fatty acids min-1 ml-1 plasma. This heparin-induced response of plasma LPL was not different between resting controls and exercised fish. Heparin or prolonged swimming had no effect on the concentration/composition of lipoproteins that contain 92% of the energy in total plasma lipids. We conclude that (1) red muscle LPL is strongly activated by endurance swimming, (2) rainbow trout have a high reserve capacity for hydrolyzing lipoproteins, and (3) future studies should aim to measure lipoprotein flux because their concentration does not reflect changes in flux. These novel characteristics of fish LPL imply that lipoproteins are used as a metabolic shuttle between fat reserves and working muscles, a strategy exploiting an abundant source of energy in rainbow trout. [ABSTRACT FROM AUTHOR]

While many coral reef fishes utilise substratum refuges, the direct influence of water flow and swimming ability on such refuging patterns is yet to be established. This study examined the swimming ability and refuging behaviour of a labrid (Halichoeres margaritaceus) and a pomacentrid (Pomacentrus chrysurus) that inhabit high flow, wave-swept coral reef flats. Field observations of refuging patterns were combined with experimental evaluations in a flow tank using a replica of a substratum hole frequently used by these species. Under a range of flow speeds commonly found on the reef flat (0–60 cm s-1), flow within the substratum refuge was reduced to speeds of 0–12 cm s-1, representing a 75–100% flow reduction. Swimming ability of each species was then tested at 60 cm s-1 with and without access to this flow refuge. Both species were able to maintain activity within the 60 cm s-1 flow for considerably longer when provided with a refuge, with increases from approximately 39 min to 36 h for H. margaritaceus and 8 min to 88 h for P. chrysurus. Despite H. margaritaceus having the strongest swimming ability without access to a refuge, P. chrysurus was able to maintain swimming activity more than twice as long as H. margaritaceus when provided with a refuge. These increases in activity are probably due to energetic savings, with this type of refuge providing an estimated 95% energy saving over swimming directly into a unidirectional flow of 60 cm s-1. These results highlight the major advantages provided by refuging behaviour and emphasise the importance of habitat refuges in shaping patterns of habitat use in reef fishes. [ABSTRACT FROM AUTHOR]

Juvenile matrinxã, Brycon cephalus, were submitted to sustained swimming for 72 days at 1.0 body length s-1. Exercised fish (EF) grew more than non-EF and their feed conversion ratio (FCR) improved; haematological responses demonstrated a decrease in haemoglobin and mean cell haemoglobin contents and increase in the mean cell volume. In the plasma, sodium, ammonia and amino acid concentrations increased; plasma triglycerides decreased while free fatty acids increased. Liver glucose, free amino acids, ammonia, the rate protein per fish weight and total lipid content increased, while the glycogen per fish ratio declined. Glutamate dehydrogenase (GDH) activity increased while pyruvate kinase (PK) and lactate dehydrogenase (LDH) decreased. White muscle glucose, lactate, the glycogen per fish-weight ratio and total lipid content exhibited a decrease in their values; ammonia, free amino acids and the protein per fish-weight ratio increased. GDH and PK decreased their activities. In the red muscle glycogen store, the glycogen per fish-weight ratio and glucose were reduced. Juvenile matrinxãs, under sustained swimming, were physiologically and biochemically adapted to exercise as indicated by improved blood flow, transport and oxygen uptake, FCR, amino acid and protein incorporation and growth. Continuous exercise is a good practice for B. cephalus cultivation. [ABSTRACT FROM AUTHOR]

Sixty-four post-larvae of the King George whiting Sillaginodes punctata were tested in swimming chambers, against one of five flow-through velocities (2, 4, 6, 8 or 10 cm s−1) for up to a maximum of 120 min. Fish were determined by regression to have an FV50 (50% fatigue velocity) of 6·0 cm s−1. No fish survived the full 120 min at 10 cm s−1. Sixteen individuals were tested in a swimming chamber against a flow-through velocity of 6 cm s−1 and allowed to swim to exhaustion. Fish swam between 25 and 538 min with a peak at c. 6–8 h. Total swimming time was not correlated with standard length of fish although the size range examined was narrow. Relative to recent studies on the swimming abilities of late-stage larvae of reef fishes, this study indicates that post-larval King George whiting are weak swimmers. The weak swimming ability of post-larval King George whiting is consistent with studies showing passive dispersal and recruitment of this species. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Strenuous exercise in fish is usually a consequence of migration, reproduction, and spawning. Varying among fishes, this kind of stress is associated with blood glucose and lactate increase, in relation to which two major groups are distinguishable: the "lactate releasers" and "non-lactate releasers". Unlike strenuous exercise, sustained swimming imposes a variety of effort that results in distinct kinetic types of blood lactate and glucose. Compared to Platichthys stellatus and Oncorhynchus mikyiss, blood lactate of Salminus maxillosus (dourado) was lower after exercise, whereas recovery time was greater. Great demands were made of white muscle, and dourado is not a lactate releaser. Two different metabolic tendencies were observed in sustained and intense swimming. Gluconeogenesis was observed during recovery, as well as the alanine cycle which recomposes the lactate tissue pattern. Full recovery after intensive exertion required more than 24 hours.