Structural abnormalities of common carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> spermatozoa

Spermatozoa of common carp Cyprinus carpio are typically consist of a primitive head without acrosome, a midpiece with several mitochondria, a centriolar complex (proximal and distal centriole), and one flagellum. During an evaluation of the motility of common carp spermatozoa, we found spermatozoa with more than one flagellum and/or “double head” in three different individuals. This may be related to abnormal spermatogenesis. Ultrastructure and physiological parameters of spermatozoa were examined using light microscopy (dark field with stroboscopic illumination), transmission and scanning electron microscopy, and flow cytometry. The recorded pictures and videos were evaluated using Olympus MicroImage software. All spermatozoa with more than one flagellum had a larger head and shorter flagella. They occasionally demonstrated several cytoplasmic channels separating the flagella from the midpiece. Each flagellum was based upon its own centriolar complex, with the connection of the flagellum to the head always at a constant angle. The flagella always consisted of nine peripheral pairs and one central doublet of microtubules. Sperm exhibited a relative DNA content similar to that found in sperm from normal males, with higher coefficients of variation. Although similar abnormalities have been found in livestock, where they were described as a defect in spermiogenesis, no comparable results have been reported in fish. The frequency at which these abnormalities occurs, the fertilization ability of males with defects in spermiogenesis, the influence of these abnormalities on progeny in terms of ploidy level, and the occurrence of deformities warrant further investigation.     

Identification and expression analysis of ghrelin gene in common carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis>

ABSTRACT:   A ghrelin gene has been cloned and sequenced in common carp Cyprinus carpio . Ghrelin cDNA is composed of 461 bp [with a 36-bp 5'-untranslated region (UTR) and a 113-bp 3'-UTR], which translates into a protein of 103 amino acid residues. Carp ghrelin (preproghrelin) contained a predicted signal peptide of 26 amino acid residues, the ghrelin domain ( Gly ²⁷– Val ⁴⁵) and C-terminal peptide ( Gly ⁴⁶– Phe ¹⁰³). Homology analysis of the ghrelin domain of carp with that of other known ghrelin in vertebrates showed good similarity to teleost ghrelin (50–81.8%). Hydropathy analysis based on the deduced amino acid sequence of ghrelin domains in teleosts showed a similar profile. Carp ghrelin clustered with ghrelin of goldfish Carassius auratus and other teleosts, away from mammalian, reptilian, avian, amphibian and chondrichthian ghrelin, by phylogenetic analysis. Genomic organization of carp ghrelin gene was composed of four exons and three introns, which was the same as that of other teleosts and human ghrelin genes. The carp ghrelin gene was expressed in unstimulated tissues such as foregut, hindgut, spleen and brain. In spleen cells, expression of the ghrelin gene increased upon stimulation with lipopolysaccharide (LPS), phytohemagglutinin (PHA) or imiquimod. The identification of carp ghrelin gene and the analysis of the modulation of its expression in immune-activated conditions will allow a more complete analysis of the roles of ghrelin in teleosts.     

Aluminum-induced oxidative stress in lymphocytes of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>)

Several studies of fish have shown that aluminum may induce hypoxia, hypercapnia, metabolic acidosis, and respiratory failure. In lymphocytes, morphologic abnormalities and reduced immune activity have been observed. Nevertheless, there is little data on oxidative stress and such data are essential in order to identify its mechanism of action. The common carp Cyprinus carpio, an omnivorous fish commonly used in commercial aquaculture, has been proposed as a test organism in toxicologic assays due to its economic importance and wide geographic distribution. The aim of this work was to evaluate Al-induced oxidative stress in lymphocytes of the common carp C. carpio. Specimens were exposed to three different concentrations of Al (0.05, 120, and 239 mg/l) in a static exposure system for 96 h. At the end of the exposure period, blood was collected and lymphocytes were separated. Lipid peroxidation, oxidized protein content and the activity of superoxide dismutase, catalase, and glutathione peroxidase were measured. Results show that the tested Al concentrations modified the activity of antioxidant enzymes and elicited higher levels of lipid peroxidation and oxidized proteins. The degree of damage induced was concentration and tissue dependent.     

Physiological responses of over-wintering common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) to disturbance by Eurasian otter (<Emphasis Type="Italic">Lutra lutra</Emphasis>)

Using a tame animal, the impact of otter (Lutra lutra) disturbance on over-wintering carp (Cyprinus carpio) was monitored in two experiments, 133 and 140 days, respectively, over two consecutive winters (November–April). The level of stress in over-wintering carp exposed to various intensities of disturbance by otters was quantified using biological indicators of stress (cortisol, cortisone, indices of nitrogen, carbohydrate, lipid and mineral metabolism and activity of basic blood plasma enzymes) taken from blood plasma of stocked carp at the end of the winter seasons (when the photoperiod was 12 light:12 dark, respectively, 13L:10D). Moreover, condition (Fulton’s coefficient of condition and fat content in muscles) and mortality rate of that carp were measured after over-wintering and also after the subsequent vegetation period. The analysis of blood and tissue samples of experimental fish showed changes in nitrogen, carbohydrate and mineral metabolism as well as levels of hormones and fat reserves. Higher response to stress in metabolism of carp with lower intensity of disturbance by otter suggests that high level of disturbance can lead to metabolic adaptation of carp to stress. The effect of stress on the mortality rate of carp during the over-wintering is not clear. Nevertheless, the negative effect of stress on survival, condition and growth rate of carp in the subsequent vegetation period was not observed.     

Behavioural response of carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>, L.) pond stock upon occurrence of hunting great cormorant (<Emphasis Type="Italic">Phalacrocorax carbo sinensis</Emphasis>) flocks

Besides various physiological and biological indices, stress in fish can be expressed directly by changes in their behaviour. Electrofishing point sampling approach based on CPUE (catch per unit effort) was used to evaluate fish density (escapement) into the littoral zones of four Czech ponds as a reaction to the occurrence and hunting activities of great cormorant (Phalacrocorax carbo sinensis) flocks. The behaviour of two-year-old common carp (Cyprinus carpio) before and after cormorant arrival was compared. Significant differences (P < 0.001) in CPUE were recorded in fish density before and after cormorant arrival on all of four ponds under study—Žofinsky: 0.04 ± 0.18 and 22.38 ± 26.87 (mean ± SD), Stary Hospodář: 0.05 ± 0.29 and 25.49 ± 25.45, Žebrákov: 0.16 ± 0.57 and 28.58 ± 24.75 and Travičny: 0.03 ± 0.19 and 17.18 ± 18.20, respectively. The evaluation of fish wounding in the CPUE fish samples proved the proportion of fish injured by cormorant attacks ranging from 3.33 to 18.19% in the ponds under study.     

In vitro toxicology test system based on common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) sperm analysis

The effect of heavy metals on the motility parameters of common carp sperm was investigated. In vitro test systems are widespread in ecotoxicology, and fish sperm can be a suitable model. For this reason, studies had been carried out in this topic; however, the published methods are not standard in several aspects (donor species, measured endpoint, etc.). In this study, a previously published toxicology-aimed sperm analysis protocol was tested to examine the effect of heavy metals (arsenic, cadmium, chromium, copper, mercury, nickel, zinc,) on common carp sperm. According to our results, PMOT is the most sensitive of the investigated parameters: dose-response was observed in case of each metal at low concentrations, already after 30 min of exposure. VCL was less sensitive: lower effects were observed at the same concentrations compared to PMOT. Among the examined parameters, LIN was the least affected: a dose-response was observed only in case of arsenic and mercury. The same sensitivity of motility parameters was observed on zebrafish sperm previously. Moreover, we found that PMOT, VCL, and LIN of common carp sperm were affected at the same concentrations as it had been observed in zebrafish, when the identical analytical protocol was applied. The only exception was As³⁺, where common carp sperm proved to be more sensitive: lower concentrations already reduced its motility parameters. Consequently, PMOT of common carp sperm is an accurate and fast bioindicator of aquatic pollution.     

Haematopoiesis in the head kidney of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.): a morphological study

The morphogenesis of head kidney haematopoietic cells in common carp has been shown to be very similar to that of higher vertebrates. The erythropoietic series consisted of the erythroblasts (basophilic, polychromatic and orthochromic), young erythrocyte and erythrocyte. The morphological changes that occur during maturation process are reduction in size and further increase at mature stage, gradual chromatin condensation and the increase in haemoglobin content. Maturation stages of neutrophils and basophils encompassed the young progranulocyte, progranulocyte and metagranulocyte. The early blast cells, basophilic lineage and lymphocytes were regularly present in kidney. In the monocytoid series in kidneys, promonocytes and mature monocytes were observed. Precursor stages of the eosinophile and thrombocyte were not discernible (although mature cells were observed). Lymphoid cells were the most abundant, followed by granuloid, thrombocyte, erythroid, blast and monocytoid cells. The neutrophilic progranulocyte was the most frequent granuloid cell. The lymphocyte was the most frequent cell in the kidney and the most numerous of the lymphoid lineage.     

The common carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> in Croatia (Danube and Adriatic basins): a historical review

This review provides the first historical account of the ecology and biology of common carp Cyprinus carpio in the Danube and Adriatic basins of Croatia, and emphasises the species’ economic relevance and management implications. As a semi-native species that is native to the Danube but translocated across the Adriatic Basin, carp plays an important role for aquaculture, recreational and artisanal fisheries. However, original strains have now disappeared, and because of genetic pollution in inland waters there is an increasing demand for restoring populations of the now rare and threatened wild carp, making conservation measures a priority. Translocations of carp across water bodies of the Adriatic Basin mostly for food supply did not prove successful in the long term, as the resulting ecological impacts may have been higher than the expected economic advantages. Measures for the prevention of further (uncontrolled) carp re-stocking are therefore necessary and this will require closer collaboration between scientists and environmental managers.     

Dietary inclusion of detoxified <Emphasis Type="Italic">Jatropha curcas</Emphasis> kernel meal: effects on growth performance and metabolic efficiency in common carp, <Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.

Jatropha curcas is a multipurpose and drought-resistant shrub or small tree widespread all over the tropics and subtropics. Its seeds are rich in oil, and the Jatropha kernel meal obtained after oil extraction is rich in protein. However, presence of toxic and antinutritional constituents restricts its use in fish feed. Jatropha kernel meal was detoxified. Common carp, Cyprinus carpio, fingerlings (15; av. body mass 10.9 ± 0.65 g) were randomly distributed in three groups with five replicates. A 6-week feeding experiment was conducted in a respirometer system to evaluate the growth performance, nutrient utilisation and energy budget. Fish were fed isonitrogenous diets (38% crude protein): control diet (C _ontrol group) containing fish meal (FM) protein based protein and two other diets replacing 75% FM protein with detoxified Jatropha kernel meal (DJKM, J _atropha group) and soybean meal (SBM, S _oybean group). At the end of the experiment, body mass gain, metabolic growth rate, protein efficiency ratio, protein productive value, energy retention, efficiency of metabolised energy for growth and efficiency of energy retention were determined. These parameters were high and statistically similar for C _ontrol and J _atropha groups and significantly lower (P < 0.05) for S _oybean group. Whereas a reverse trend was observed for energy expenditure per g protein retained in fish body. No significant differences were found in heat released, gross energy uptake, metabolised energy intake, metabolisability, energy expenditure, energy expenditure per g protein fed and apparently unmetabolised energy. Conclusively, common carp–fed plant protein (DJKM and SBM) and FM protein–based diets exhibited equal average metabolic rate.     

Rapid measurements of fat content in live and slaughtered common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

The objective of this study on common carp (Cyprinus carpio) was to obtain and predict the first cross-validated data of the fat content on market size carps using a non-invasive or non-destructive method in situ. The carps (1680 ± 388 g; n = 136) used were from a semi-intensive system and were on a different diet (cereal, pelleted and extruded diet). For the evaluation of the fat content, a Fish Fatmeter FM 692 from Distell.com. (FFM) and a manual measurement of back fat height using a digital calliper were used. For the prediction model, the following basic body measurements (variables) were used: total body length, body length, body height, the width of the body, and the circuit of the body. The body weight, weight of intestines, weight of gonads, weight of hepatopancreas, and fillet yield (%) were measured, and the Fulton coefficient was calculated. The study was focussed on evaluating the applicability of these methods and the accuracy of the obtained result, respectively. Results showed that all the rapid methods had a strong correlation. Multiple regression models with forward selection of variables were used throughout. The final prediction model between predicted and observed values for the fat content for FFM and calliper being adjusted index of determination is shown here (R _adj ²  = 0.88; 5 variables and R _adj ²  = 0.91; 7 variables), respectively.     

Low levels of cadmium exposure induce DNA damage and oxidative stress in the liver of Oujiang colored common carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> var. <Emphasis Type="Italic">color</Emphasis>

Cadmium (Cd) compounds are widely distributed toxic environmental and industrial pollutants, and they may bring danger to growth and development of aquatic organisms. In China, the Oujiang color common carp, Cyprinus carpio var. color, is a very important fish, from an economic point of view, and is well used for fish culture in paddy fields. The purpose of this study was to show the low concentrations of cadmium-induced oxidative stress response and DNA damage in the livers of Cyprinus carpio var. color. Superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione (GSH) in liver were measured after exposure to Cd levels (0.41, 0.52, 0.69, 1.03 and 2.06 mg/L, respectively) for 7 days and compared with the control groups. DNA damage, including indicators of damage percentage, DNA tail length (TL) and DNA tail moment (TM) were also analyzed by comet assays. Results showed that MDA and GSH levels in all treatment groups increased significantly relative to the controls (P < 0.01). Treatment with Cd at concentration of 0.41 mg/L increased SOD activity, while treatment with Cd at concentrations >0.41 mg/L inhibited SOD activities. DNA damage percentage, TL and TM also significantly increased when the Cd level was >0.41 mg/L. Positive correlations were also found between DNA damage levels and MDA levels (r = 0.74 for DNA damage percentage, r = 0.83 for TL, r = 0.84 for TM; P < 0.01 for all) as well as between GSH and MDA levels (r = 0.77, P < 0.01). These results strongly suggested that Cd-induced DNA damage in the livers of Cyprinus carpio var. color was due to lipid peroxidation and oxidative stress.     

Effect of glyphosate-based herbicide on hematological and hemopoietic parameters in common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L)

The effects of Roundup (glyphosate-based herbicide) on peripheral blood parameters and hematopoietic tissue cellular composition and activity in common carp juveniles were evaluated. The fish were exposed for 7 days at 0.0, 0.1, 0.5, or 5.0 mg/L of glyphosate. In fish exposed to Roundup, hematological alterations were observed; however, most of them were not directly related to the herbicide concentration. An increase in Ht and MCV, and decrease in Hb, MCH, and MCHC compared to the control were observed. Fish exposed to Roundup showed also a reduction in WBC and oxidative metabolic activity of phagocytes (NBT) compared to the control. The fish exposed to 0.1 and 5.0 mg/L showed increased glucose values, whereas in those subjected to 0.5 mg/L blood glucose concentration declined compared to the control. Cholesterol significantly increased at 0.1 mg/L and decreased at 5.0 mg/L. Analysis of head kidney hematopoietic tissue revealed that Roundup at concentrations 0.5 and 5.0 mg/L caused a significant increase in the rate of cell proliferation accompanied by an increase in frequency of early blast cells. No significant differences occurred in percentages of most cell lineages but the frequency of monocytoid, eosinophilic, and basophilic lineage cells significantly increased in the herbicide-exposed fish compared to the control. The obtained results revealed that sublethal concentrations of Roundup that may occur in polluted natural waters caused a slight anemic and significant immunosuppressive response in common carp juveniles. On the other hand, they indicate a considerable compensatory potential of carp hematopoietic system.     

The effects of Roundup on gametes and early development of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L)

To determine the effects of Roundup, a commercial formulation of glyphosate, gametes, and embryos of common carp (Cyprinus carpio L) was exposed to wide range of herbicide concentrations (0.0, 0.1, 0.5, 2.0, 5.0, 10.0, 20.0, and 50.0 mg/l). The obtained results showed different effects of Roundup on common carp gametes. Herbicide reduced swelling of eggs (but the effect was not concentration-related), while sperm showed low sensitivity to Roundup (time of spermatozoa motility was reduced in a significant way only at 20 mg/l, and at remaining concentrations, only a slight tendency was observed). During the embryonic development, Roundup caused a decrease of common carp embryonic survival (and the effect was concentration-related); however, it had no effect on development rate. During the embryogenesis, three types of embryo body malformation were observed: yolk sac edema, spine curvature, and shortening of body, but their frequencies were not associated with the presence or concentration of herbicide. However, Roundup affected quality of newly hatched larvae of common carp by increasing their mortality. No effect of herbicide on percentage of deformed larvae was observed but larvae hatched in water with Roundup tended to show more complex anomalies compared to those from the control. Obtained data showed that even low concentrations of this herbicide in waters can significantly reduce egg swelling, survival of embryos, and quality of fish larvae.     

Environmental quality and natural food performance at feeding sites in a carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) pond

Just like other domesticated animals, common carp (Cyprinus carpio) are able to learn where food can easily be obtained. As a result, carp in semi-intensive polyculture ponds could conceivably restrict their main activity centres to supplemental feeding sites, leading to lowered exploitation of natural food resources (zooplankton and macrozoobenthos) and localised degradation of environmental conditions. At two semi-intensive ponds in southern Moravia (Czech Republic), areas around feeding sites displayed significantly reduced oxygen concentration and saturation (mainly p < 0.001). Likewise, temperature, pH and transparency also decreased significantly at feeding sites (mainly p < 0.05), while turbidity increased. While there was no significant difference in zooplankton biovolume at feeding and non-feeding sites, zoobenthos density and biomass were significantly lower at feeding sites (mainly p < 0.01). The feeding behaviour of carp, therefore, led to significant changes in both abiotic and biotic conditions at supplemental feeding sites.     

Growth,hematological and biochemical indices of common carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> fed diets containing corn gluten meal

The effects of replacing fish meal (FM) with corn gluten meal (CGM) on growth and physiological performance were evaluated in common carp (Cyprinus carpio). Six experimental diets were formulated by substituting 0 (control), 20, 40, 60, 80, and 100% CGM protein for FM protein. The concentrations of dietary protein in the experimental diets were 27.8–29% and the P:E ratios were 14.7–15.46 mg/kJ. Eighteen fish with an initial weight of 13.5?±?0.1 g were allocated to each of 18 circular tanks (450 L) to give triplicate groups for each dietary treatment. The fish were fed to satiation for 8 weeks. At the end of the feeding trial, growth indices, body proximate composition, and hematological and biochemical parameters were measured. Blood samples were taken from six fish in each tank. Final weight and total length were significantly higher in fish fed 100% CGM (27.8?±?1.2 g and 11.9?±?0.3 cm) than for those fed the control (22.7?±?1.4 g and 10.9?±?0.5 cm) or 20% CGM (22.3?±?1.2 g and 11?±?0.4 cm) diets. No effect of FM replacement by CGM was observed for condition factor or hepatosomatic index (P?>?0.05). The highest value of protein productive value (14.31?±?0.65) was observed in fish fed 20% CGM (P?<?0.05). There were no significant differences in percentage body moisture and fat, but percentages of protein and ash were significantly different among experimental groups; the highest values of protein (15.6?±?0.24%) and ash (3.01?±?0.26%) were recorded in fish fed 40% CGM. For hematological parameters, the highest number of white blood cells (4.1?±?0.1?×?10³ mm^?3) was observed in fish fed 100% CGM (P?<?0.05). In addition, the highest hematocrit (42.1?±?0.7%) and triglyceride (294.11?±?23.82 mg dl^?1) were seen in fish fed the diet containing 40% CGM, while 80% CGM gave the highest cholesterol level (204.44?±?9.0 mg dl^?1; P?<?0.05). Replacement of FM with CGM had no negative effects on growth and physiological parameters of common carp fingerlings in this short (8 weeks) trial, suggesting that it may be feasible to replace FM with CGM in diets formulated for juvenile common carp.     

Immunogene expression in head kidney and spleen of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.) following thermal stress and challenge with Gram-negative bacterium, <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

To evaluate the effect of thermal and microbial stress on the immune response of common carp (Cyprinus carpio L.), relative mRNA expression level of pro-inflammatory cytokines [tumor necrosis factor alpha (TNF-α) and interleukin (IL)-1β] and other genes related to immune or stress response [inducible nitric oxide synthase (iNOS), heat shock protein 70 (Hsp70), superoxide dismutase one (SOD1), and glucocorticoid receptor (GR)] was measured by quantitative PCR (qPCR). In addition, total protein and total immunoglobulin level in blood plasma of experimental common carp was also assayed. All the above parameters were estimated 24 h post-challenge with Gram-negative bacterium, Aeromonas hydrophila. Common carp (54.89?±?6.90 g) were initially exposed to 20 °C (control group) and 30 °C (thermal stress group) water temperature for 30 days, followed by experimental challenge with 2.29?×?10⁸ colony forming unit/mL (CFU/mL; LD₅₀ dose) of A. hydrophila. Exposure of fish to thermal stress and subsequently challenge with A. hydrophila significantly (P?<?0.05) increases the IL-1β mRNA expression in head kidney and spleen of common carp by ~?39.94 and ~?4.11-fold, respectively. However, TNF-α mRNA expression in spleen decreased ~?5.63-fold in control fish challenged with A. hydrophila. Thermal stress and challenge with bacterium suppresses the iNOS and GR mRNA expression in spleen of common carp. Moreover, significant (P?<?0.05) increase in total protein content of blood plasma (~?43 mg/g) was evident in fish exposed to thermal stress and challenged with A. hydrophila. In conclusion, our study highlights the importance of elevated temperature stress and microbial infection in differential regulation of expression of several immunogenes in common carp.     

Spatial learning-induced <Emphasis Type="Italic">egr</Emphasis>-<Emphasis Type="Italic">1</Emphasis> expression in telencephalon of gold fish <Emphasis Type="Italic">Carassius auratus</Emphasis>

The immediate-early gene (egr-1) expression was used to examine the neuron’s response in telencephalon of goldfish during spatial learning in small space. Fishes were pre-exposed in the experimental apparatus and trained to pick food from the tray in a rectangular-shaped arena. The apparatus was divided into identical compartments comprising three gates to provide different spatial tasks. After the fish learned to pass through the gate one, two more gates were introduced one by one. Fish made more number of attempts and took longer time (P < 0.05) to pass through the first gate than the gate two or three. This active learning induces the expression of egr-1 in telencephalon as established by western blot analysis. Subsequently, the fish learn quickly to cross the similar type of second and third gate and make fewer errors with a corresponding decline in the level of egr-1 expression. As the fish learned to pass through all the three gates, third gate was replaced by modified gate three. Interestingly, the level of egr-1 expression increased again, when the fish exhibit a high exploratory behavior to cross the modified gate three. The present study shows that egr-1 expression is induced in the telencephalon of goldfish while intensively acquiring geometric spatial information to pass through the gates.     

Energy balance of juvenile <Emphasis Type="Italic">Cyprinus carpio</Emphasis> after a short-term exposure to sublethal water-borne cadmium

Stress in fish can be assessed by means of a bioenergetic approach, based on the evaluation of changes in their physiological parameters. The objective of this study was to determine the impact of sublethal water-borne cadmium (Cd) on the energetic balance of juvenile Cyprinus carpio under laboratory conditions after a short-term exposure. Fish were exposed to a concentration of Cd (0.15 mg Cd l⁻¹) for 2 weeks. This concentration is environmentally realistic since it is usually found, even at higher values, in heavily polluted periurban water bodies of Argentina. No mortality was recorded among the animals used in the experiments. Food intake, food assimilation and assimilation efficiency, fecal production, liver glycogen content, oxygen consumption, oxygen extraction efficiency, specific metabolic rate, ammonia excretion and ammonia quotient (AQ), condition factor, and liver somatic index were determined. The overall balance was expressed as the scope for growth (SFG). The morphological indices and the liver glycogen content of Cd-exposed fish showed no significant differences when compared to those of controls. There was a significant decrease in the food intake, fecal production, and food assimilation rates as well as in AQ; the SFG exhibited a highly significant decrease. The remaining parameters (assimilation efficiency, oxygen consumption, oxygen extraction efficiency, specific metabolic rate, and ammonia excretion) increased after the exposure to Cd. We concluded that the sub-chronic exposure of Cyprinus carpio to a sublethal concentration of Cd causes important alterations in the energy-related homeostasis of fish. Most of the responses are indicative of physiological adaptations to compensate an increased energy requirement due to the impairments caused by the metal.