Comparison of the swimming performance of farmed and wild gilthead sea bream, Sparus aurata

Farmed gilthead sea bream, Sparus aurata, frequently escape from the sea cages and interact with wild populations. The impact of these interactions on the wild populations will depend, in part, on differences in performance of the bream. This study compared the swimming performance of the wild and farmed fish in a current channel. The absolute critical swimming speed (U_crit) increased with increasing size while the relative U_crit decreased. Even at the same length there were noticeable performance differences between the individuals. The wild sea bream have significantly higher (P<0.05) absolute U_crit performance (0.86±0.01 m s⁻¹) than the farmed fish (0.79±0.01 m s⁻¹) and significantly higher (P<0.05) relative U_crit performance (4.52±0.05 BL s⁻¹) than the farmed fish (4.21±0.05 BL s⁻¹). The present study suggests that cultured sea bream may not have the ability to compete with wild sea bream in native seawaters.     

Effects of Loma morhua (Microsporidia) infection on the cardiorespiratory performance of Atlantic cod Gadus morhua (L).

The microsporidian Loma morhua infects Atlantic cod (Gadus morhua) in the wild and in culture and results in the formation of xenomas within the gill filaments, heart and spleen. Given the importance of the two former organs to metabolic capacity and thermal tolerance, the cardiorespiratory performance of cod with a naturally acquired infection of Loma was measured during an acute temperature increase (2 °C h^?1) from 10 °C to the fish's critical thermal maximum (CT_Max). In addition, oxygen consumption and swimming performance were measured during two successive critical swimming speed (U_crit) tests at 10 °C. While Loma infection had a negative impact on cod cardiac function at warm temperatures, and on metabolic capacity in both the CT_Max and U_crit tests (i.e. a reduction of 30–40%), it appears that the Atlantic cod can largely compensate for these Loma‐induced cardiorespiratory limitations. For example, (i) CT_Max (21.0 ± 0.3 °C) and U_crit (~1.75 BL s^?1) were very comparable to those reported in previous studies using uninfected fish from the same founder population; and (ii) our data suggest that tissue oxygen extraction, and potentially the capacity for anaerobic metabolism, is enhanced in fish infected with this microsporidian.     

Effects of Chronic Aluminum Exposure on Swimming and Cardiac Performance in Rainbow Trout, <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

Rainbow trout were exposed to 0–80 μg l⁻¹ aluminum (Al) at pH 5.2 in synthetic soft water, for up to 8 weeks. Trout were submitted to an incremental swimming test to quantify their aerobic swimming capacity (U_crit). After a simple, non-invasive cardiac surgery to install Doppler flow probes, their heart rate, cardiac output and stroke volume were measured while swimming at increasing water velocities. Fish exposed to Al accumulated significant amounts of Al at the gills (0–80 μg g⁻¹) and in their liver (5–60 μg g⁻¹) and had decreases in swimming capacity, ranging from 11 to 21%. Analysis of cardiac parameters during swimming revealed that increases in heart rate were used in trout exposed to the highest concentrations of Al to increase cardiac output, whereas control fish tended to increase cardiac output through increases in stroke volume.     

Dietary fatty acid composition influences swimming performance in Atlantic salmon (Salmo salar) in seawater

Swimming performance was measured in Atlantic salmon (Salmo salar, L.) fed one of four isonitrogenous and isoenergetic experimental diets, in which the supplemental lipid (25% of diet) originated either solely from menhaden oil (rich in highly unsaturated fatty acids of the n-3 series; n-3 HUFA), or from different proportions of this oil and canola oil (rich in 18-carbon unsaturated fatty acids).The results indicate that dietary fatty acid composition influenced swimming performance in Atlantic salmon through changes in maximum swimming speed (U_crit). Salmon fed a diet in which menhaden oil furnished all of the supplemental lipid had a significantly lower U_crit than those fed a diet in which the supplemental lipid was an equal blend of menhaden and canola oil. Furthermore, there was a highly significant linear relationship between dietary and/or muscle levels of particular fatty acids or groups of fatty acids and U_crit.There was a negative relationship between dietary n-3 HUFA content and U_crit, but there was no relationship between U_crit and muscle n-3 HUFA content nor between U_crit and the levels of the eicosanoids thromboxane A₂ and prostacyclin, or of their ratio, in the heart and gills of fatigued salmon. These results indicate that the differences in exercise performance were not a result of differences in n-3 HUFA metabolism amongst the dietary groups.Indeed, although there was a highly significant positive relationship between U_crit and total n-6/n-3 fatty acid ratio of muscle lipids, this was largely due to the associated positive relationship between U_crit and content of the most common n-6 fatty acid in muscle lipids, linoleic acid. There was also a significant positive relationship between content in muscle lipids of the most prominent fatty acid in canola oil, oleic acid, and U_crit. It is suggested that metabolism of these 18-carbon unsaturated fatty acids accounts for the effects of the diets on exercise performance.     

A comparison of constant acceleration swimming speeds when acceleration rates are different with critical swimming speeds in Chinese bream under two oxygen tensions

To investigate the effect of acceleration rates on the constant acceleration test speed (U _cat) and to compare U _cat with the critical swimming speed (U _crit) in Chinese bream (Parabramis pekinensis), the U _cat test at acceleration rates of 0.05, 0.1, 0.2, 0.4 and 0.8 cm s^?2 and the U _crit test in juvenile fish at 20 °C in either normoxia (>90 % saturation oxygen tension) or hypoxia (30 % saturation) were compared. The lactate concentration ([lactate]) of white muscle, liver and plasma and the glycogen concentration ([glycogen]) of white muscle and liver were also measured to identify whether tissue substrate depletion or tissue lactate accumulation correlated with exhaustion. The U _cat decreased with the acceleration rate, and there was no significant difference between U _crit and U _cat at lower acceleration rates. Hypoxia resulted in lower U _cat and U _crit, and the difference increased with decreased acceleration rates of the U _cat test, possibly due to the increased contribution of aerobic components in U _crit or U _cat at low acceleration rates. Hypoxia elicited a significant decrease in muscle [glycogen] and an increase in muscle and liver [lactate] in resting fish. All post-exercise fish had similar muscle [lactate], suggesting that tissue lactate accumulation may correlate with exercise exhaustion. Unlike hypoxia, exercise induced an increase in muscle [lactate] and a significant increase in plasma [lactate], which were worthy of further investigation. The similar swimming speed and biochemical indicators after exercise in the U _crit and U _cat groups at low acceleration rates suggested that U _cat can be an alternative for the more frequently adopted protocols in U _crit in Chinese bream and possibly in other cyprinid fish species.     

Swimming performance of brown trout and grayling show species‐specific responses to changes in temperature

Fishways have historically been constructed to restore and preserve the ecological connectivity for fish in fragmented rivers. However, the fishways are often selective on species due to different size and swimming capacity. As the proportion of dammed rivers is still increasing, there is a growing need for more information on wild fish and their migration potential. In this study, we compared the swimming capacity of wild caught brown trout (Salmo trutta) and European grayling (Thymallus thymallus) until the fish were exhausted in a critical swimming speed (U_crit) test, under three different naturally occurring stream temperatures in Norway: 1.7, 5.5 and 10°C. The results indicated that trout swim better at the warmer temperatures than at colder temperatures. The grayling showed consistent swimming patterns with little variation across all tested temperatures. The results therefore signify the need to have operational fishways already early in the spring when the grayling migration starts and highlight the need for more studies on fish migration abilities across a wider range of species and seasons.     

Effects of size and sex on swimming performance and metabolism of invasive mosquitofish Gambusia holbrooki

In freshwater ecosystems, abiotic factors such as flow regime and water quality are considered important predictors of ecosystem invasibility. The aim of this study was to investigate the critical swimming capacity and metabolism of the eastern mosquitofish, Gambusia holbrooki, focusing on sex and size effects, to evaluate the influence of water flow on its invasive success. Specimens of mosquitofish were captured from the Ter Vell lagoon (L'Estartit, north‐eastern Spain) in July 2014, and we measured the critical swimming speed (U_crit) and oxygen consumption of individual fish (30 females and 30 males) using a mini swim tunnel. The mean U_crit of this poeciliid fish was estimated at 14.11 cm·s^?1 (range = 4.85–22.26), which is lower than that of many other fishes of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alterations. However, the U_crit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same body mass, and thus probably being more resistant to strong water flows. Multiple regression models illustrate that multivariate analyses might increase the predictive power and understanding of swimming performance and metabolic traits, compared to results from conventional simple regressions.     

Does the aerobic capacity of fish muscle change with growth rates?

To ascertain whether growth rate modifies the oxidative capacity of fish white muscle, we examined the effects of individual growth rate on the activities of four mitochondrial enzymes in white muscle of the fast growing Atlantic cod,Gadus morhua. Growth rates were individually monitored in cod held at three acclimation temperatures during experiments repeated in four seasons. The size dependence of citrate synthase (CS), cytochrome C oxidase (CCO) and β-hydroxyacyl CoA dehydrogenase (HOAD) activities was established using wild cod ranging from 115 to 17,350 g. Given their negative allometry, CS and CCO activities in the experimental cod were corrected to those expected for a 1.2 kg animal. HOAD activities did not change with size. The specific activities of CCO and CS were positively correlated with growth rate. However, for both enzymes, season explained more of the variability than growth rate or temperature. Season was the only factor to significantly affect the activity of HOAD, while temperature and season interacted to determine glutamate dehydrogenase activity. CS activity was positively correlated with the initial condition of the cod, which differed among the seasons. The other enzymes did not show this relationship. The independent changes of these enzymes suggest that mitochondria undergo qualitative modifications with changes in growth rate, season and size. Although growth rate and the activities of CCO and CS are positively correlated, the activity of the mitochondrial enzymes is more affected by size, physical condition and season.     

Effect of lordosis on the swimming performance of juvenile sea bass (Dicentrarchus labrax L.)

The critical swimming speed (U_crit, cm s⁻¹) value of normal juvenile sea bass (Dicentrarchus labrax) (64.7±6.33) was significantly higher than that of fish with lordosis (60.3±6.66) (P<0.05). Both normal fish and those with lordosis showed increased endurance with increasing length during exercise at a fixed water velocity of 50 cm s⁻¹. This speed was used to investigate the separation possibility of deformed specimen from the normal developed fish based on their swimming performance, and 28% separation was achieved without losing any normal fish by the end of the 10th minute. To achieve a better separation of the deformities from the normal, first grading of the juveniles and then a swimming endurance test is advised.     

The effect of migration distance and timing on metabolic enzyme activity in an anadromous clupeid, the American shad (Alosa sapidissima)

The American shad (Alosa sapidissima) is a common anadromous fish species with ecological and economic importance on the east coast of North America. This iteroparous species undergoes an energetically costly upriver spawning migration in spring. To evaluate metabolic changes associated with this migration, we assessed the maximum activity of five metabolic enzymes (citrate synthase (CS), phosphofructokinase (PFK), lactate dehydrogenase (LDH), -hydroxyacyl coenzyme A dehydrogenase (HOAD), alanine aminotransferase (GPT)) in liver, red muscle and white muscle during upstream migration in two successive years in the Connecticut River. For aerobic capacity (CS), glycolytic capacity (LDH) and utilization of stored lipid and protein energy (HOAD and GPT), there is a general pattern of increasing activity with a subsequent decline at the most upriver sites. Red muscle CS activity increased by as much as 40% during the migration while white muscle CS activity was 120% higher in the river than in the ocean. In contrast, muscle anaerobic capacity, indicated by PFK, was low as fish entered the river and then increased 5-fold at the most upriver sites. White muscle HOAD increased 30% while red muscle HOAD and muscle GPT increased as much as 60%. There were interannual and sex-associated differences in enzyme activity during upstream migration and through time at a single location. In some cases interannual differences can be larger than those seen during upriver migration as in the case of red muscle CS where sampling years differed by 125%. These interannual differences may be a result of differing river conditions that affect migratory effort. We have demonstrated that American shad use tissue and sex-specific regulation of enzyme activity during migration and we suggest that American shad metabolically acclimate to upstream migration.     

Effects of temperature and fatigue on the metabolism and swimming capacity of juvenile Chinese sturgeon (<Emphasis Type="Italic">Acipenser sinensis</Emphasis>)

Chinese sturgeon (Acipenser sinensis) is a critically endangered species. A flume-type respirometer, with video, was used to conduct two consecutive stepped velocity tests at 10, 15, 20, and 25 °C. Extent of recovery was measured after the 60-min recovery period between trials, and the recovery ratio for critical swimming speed (U _crit) averaged 91.88% across temperatures. Temperature (T) effects were determined by comparing U _crit, oxygen consumption rate (MO ₂), and tail beat frequency (TBF) for each temperature. Results from the two trials were compared to determine the effect of exercise. The U _crit occurring at 15 °C in both trials was significantly higher than that at 10 and 25 °C (p < 0.05). The U _crit was plotted as a function of T and curve-fitting allowed calculation of the optimal swimming temperature 3.28 BL/s at 15.96 °C (trial 1) and 2.98 BL/s at 15.85 °C (trial 2). In trial 1, MO ₂ increased rapidly with U, but then declined sharply as swimming speed approached U _crit. In trial 2, MO ₂ increased more slowly, but continuously, to U _crit. TBF was directly proportional to U and the slope (dTBF/dU) for trial 2 was significantly lower than that for trial 1. The inverse slope (tail beats per body length, TB/BL) is a measure of swimming efficiency and the significant difference in slopes implies that the exercise training provided by trial 1 led to a significant increase in swimming efficiency in trial 2.     

Studies on teleost corpuscles of Stannius: Physiological and biochemical aspects of synthesis and release of hypocalcin in trout,goldfish and eel

Hypercalcemia (induced by CaCl₂-injection or seawater exposure of the fish) reduced the hypocalcin content of corpuscles of Stannius (CS) in trout, goldfish and eel; concomitantly the synthetic activity of CS of hypercalcemic fish, as determinedin vitro, was enhanced. The monomeric forms of prohypocalcin and of hypocalcin of trout and goldfish are 32 and 28 kDA M_r glycoprotein species respectively; those of the eel are 2 kDa bigger,viz. 34 and 30 kDa respectively. Moreover, eel CS producein vitro an enigmatic 70 kDa glycoprotein with affinity for concanavalin-A. It is concluded that plasma calcium levels control storage and synthesis rates of hypocalcin in the CS.     

EMG telemetry studies on upstream migration of chum salmon in the Toyohira river,Hokkaido, Japan

The movements of 28 adult chum salmon, Oncorhynchus keta (Walbaum) tagged with electromyogram (EMG) transmitters were tracked along the Toyohira river, Hokkaido, Japan, in October of 2007 and 2008 to investigate and evaluate the upstream migratory behavior through the protection bed and fishway of ground sills. The approach time of fish that ascended successfully through the protection bed and fishway was shorter than that of unsuccessful fish. The unsuccessful fish were observed to swim in currents with high water velocity and shallow water depth at swimming speeds that exceeded their critical swimming speed (U _crit) during the approach to these structures. In consequence, unsuccessful fish frequently alternated between burst and maximum sustained speeds without ever ascending the fishway, and eventually became exhausted. It is important that fishway are constructed to enable chum salmon to find a passage way easily, so that they can migrate upstream rapidly without wasting excessive energy.     

Biochemical responses of matrinxãBrycon cephalus (Günther, 1869) after sustained swimming

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.     

Metabolic,behavioral, and locomotive effects of feeding in five cyprinids with different habitat preferences

Fish generally perform routine swimming behaviors during food digestion; thus, changes in swimming performance and adjustments to spontaneous behavior resulting from digestion can have important ecological significance for wild fishes. The effects of feeding on metabolism, spontaneous activity, fast-start escape movement, and critical swimming speed (U _crit) were investigated in five cyprinids with different habitat preferences, specifically the Chinese crucian carp (Carassius auratus), common carp (Cyprinus carpio), black carp (Mylopharyngodon piceus), Chinese bream (Parabramis pekinensis), and qingbo (Spinibarbus sinensis). Generally, species in still water exhibited increased feeding metabolism, whereas species in flowing water showed higher spontaneous activity and locomotion performance. Digestion had no significant effects on either spontaneous activity or fast-start escape movement in the five cyprinids. These results could be due to the small meal sizes (approximately 2% body mass) and active foraging modes of cyprinids. The changes in aerobic swimming performance due to feeding were more complex. No effect of digestion on U _crit was observed in crucian carp (still water, high feeding metabolism, and low U _crit), common carp (widely distributed, high feeding metabolism, and high U _crit), and qingbo (flowing water, low feeding metabolism, and high U _crit), but digestion resulted in a significant decrease in the U _crit of Chinese bream (moderate feeding metabolism but high U _crit) and black carp (moderate feeding metabolism and low U _crit), suggesting no connection between postprandial U _crit changes and feeding metabolism (or between U _crit and preferred habitat). The maximum metabolic rate (MMR) of common carp and crucian carp increased after feeding, whereas the corresponding values for the other three cyprinids remained the same. The oxygen uptake capacity appears to meet the oxygen demand of both aerobic swimming and digestion in common carp and crucian carp, whereas qingbo sacrifices digestion for locomotion, and black carp and Chinese bream sacrifice locomotion for digestion under postprandial swimming conditions. The locomotion-priority mode of qingbo is adaptive to its active foraging mode in the demanding swimming habitat of rapidly flowing water, whereas the high respiratory capacities of postprandial crucian carp and common carp and hence the maintenance of their aerobic swimming performances might be a by-product of natural selection for hypoxia tolerance rather than for swimming speed.     

Swimming performance,whole body ions,and gill Al accumulation during acclimation to sublethal aluminium in juvenile rainbow trout (Oncorhynchus mykiss)

Juvenile rainbow trout (2–5 g) were chronically exposed (for 22 days) to acidified softwater (Ca²⁺ = 25 Eq/l, pH 5.2) in the presence or absence sublethal Al (30 g/l). Al-exposed fish (5.2/Al group) suffered 20% whole body Na⁺ and Cl^– losses and a 30% reduction in the maximum sustainable swimming speed (U_crit) over the initial 7 days. These disturbances were approximately 2 fold greater than those observed in the fish exposed to low pH alone (5.2/0 group). However, whole body ion levels were completely restored in the 5.2/Al fish by day 22, whereas they merely stabilized at a new reduced level in the 5.2/0 group. Increased resistance to acutely lethal Al (200 g/l at pH 5.2) was observed from day 17 onwards in the 5.2/Al fish. Despite this acclimation and recovery of whole body ions, U_crit remained significantly lower than in the 5.2/0 group throughout. Growth on a restricted diet of 1% body wt. /day was normal in the 5.2/0 group compared with controls maintained in pH 6.5 softwater, whereas 5.2/Al fish suffered a 50% reduction in growth rate on the same diet. The 5.2/Al fish accumulated large amounts of Al on the gills, reaching an initial peak after 4 days, followed by a decline at 7 days, and a secondary rise thereafter. Therefore acclimation and recovery of whole body ionic status was not associated with a reduction in the gill Al burden. Some of the metabolic costs of acclimation to Al, namely a continued impairment of swimming speed and growth, are discussed in light of the physiological and structural changes reported to occur at the gills.     

Effects of soft-water acclimation on the physiology, swimming performance, and cardiac parameters of the rainbow trout, Oncorhynchus mykiss

Rainbow trout acclimated to soft water were submitted to an incremental velocity trial, and exhibited a 14% decrease in critical swimming speed (U _crit ∼ 1.37 ± 0.055 vs. 1.54 ± 0.044 m s⁻¹) compared to fish kept in hard water. After a standardized swimming protocol, soft-water-acclimated fish had higher blood lactate concentrations (6.5 ± 0.66 and 6.0 ± 0.64 mmol L⁻¹ (soft water) vs. 5.0 ± 0.46 and 3.9 ± 0.32 mmol L⁻¹ (hard water)), revealing a greater use of anaerobic metabolism for the same exercise. Cardiovascular parameters were investigated while fish were swimming at increasing water velocities, revealing that soft-water-acclimated fish had lower increases in heart rate (105% vs. 118% of pre-exercise values), due to higher heart rates observed during acclimation and during the first 10 min of the swimming trial. This was also reflected by the plateau in heart rate and stroke volume observed during the swimming protocol, which can be attributed to increased cardiovascular function in response to soft-water acclimation. These results are in accord with previously reported increases in blood-to-water diffusion distance, due to proliferation of chloride cells at the gills in response to soft-water conditions, and underscore the costs and limitations of soft-water acclimation. R. C. Playle—Deceased.     

Interaction of dietary energy levels and culture density on growth performance and metabolic and oxidative status of rainbow trout (Oncorhynchus mykiss)

Rainbow trout (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg m⁻³, D15 and D40, respectively) and two dietary energy levels (22 and 27 MJ kg⁻¹ E22 and E27, respectively) during a 75-days experimental period. At the end of the experiment, the growth rate as well as the metabolic and oxidative status of liver and muscle of fish were studied.The results showed that combination of culture density and dietaryenergy level negatively affected growth, cholesterol and LDL plasma levels and oxidative stress in muscle. Higher culture density negatively affected the values of total protein, triglycerides, and HDL in plasma, values of hepatic and muscular metabolic activities pyruvate kinase (PK), citrate synthase (CS), and hydroxiacil-CoA dehydrogenase (HOAD); glutamate pyruvate transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities in plasma, liver, and muscle; glucose 6P dehydrogenase (G6PDH) activity in muscle; and oxidative stress in liver.High energy intake, adversely affected the hepatic activity of G6PDH, HOAD, GPT and oxidative stress in muscle.Consequently our results indicate that a combination of high culture density and a high level of dietary energy (27 MJ kg⁻¹ in diet) exert a negative impact on the physiology and consequently on the welfare of the farmed fish.     

Differences in swimming performance and energetic costs between an endangered native toothcarp (Aphanius iberus) and an invasive mosquitofish (Gambusia holbrooki)

Swimming performance is a key feature that mediates fitness and survival in many fish species. Using a swim tunnel respirometer, we compared prolonged swimming performance and energy use for two competing species: an endangered, endemic toothcarp (Aphanius iberus) and a worldwide invasive mosquitofish (Gambusia holbrooki). Critical (U_crit) and optimal swimming speeds, standard and maximal metabolic rates, absolute aerobic scope, as well as the minimum cost of transport were estimated and compared between species and sexes. Body streamlining and caudal peduncle depth were also measured to explain the differences in swimming performance and efficiency. Both sexes of A. iberus presented similar swimming capacity and metabolic traits, whereas males of G. holbrooki showed higher critical swimming speeds, maximal metabolic rate and absolute aerobic scope than females. We also found marked differences between species in most of the response variables examined. Aphanius iberus showed lower swimming capacity (U_crit mean <10 cm s⁻¹), higher maximal metabolic rate and absolute aerobic scope than the invasive species. By contrast, G holbrooki swam faster and had lower cost of transport at a given fish mass and speed, thereby leading to a higher swimming efficiency. The observed differences in swimming efficiency were closely related to differences in morphological characteristics and therefore to drag pressures and propulsion. Our results add a mechanistic basis to the ecological understanding of these two species and suggest that although both are poor swimmers compared to many other similarly sized species, the native species likely has more restricted water flow tolerance and dispersal capacities.     

Muscle activity as a key indicator of welfare in farmed European sea bass (Dicentrarchus labrax L. 1758)

Groups of adult sea bass were reared at either low (10 kg m^?3) or high (50 kg m^?3) stocking densities respectively for 84 and 116 days. To monitor the red muscle activity, about 20 fish from both densities were surgically implanted with EMG (Electromyograms) radio transmitters, after EMG calibration during exhaustive swimming exercise (U_crit test). Blood samples and morphometric measurements were also taken. EMG showed that the muscle activity of fish reared at 50 kg m^?3 was on average twofold higher than fish kept at lower density. Cortisol was significantly more elevated at higher density and haemoglobin, haematocrit and RBCC (red blood cells count) showed the same trend, while lysozyme decreased. Patterns for glucose and lactate were less clear. The results showed that the contemporary use of functional (EMG) and physiological (haematological and biochemical) profiles could give a more comprehensive view of the fish status validating the diagnosis of fish stress induced by culture practices.