Juvenile Common Carp Research Articles

The molecular regulation of exercised-induced muscle fibre hypertrophy in the common carp: Expression of MyoD, PCNA and components of the calcineurin-signalling pathway

Growth was investigated over 16 d in juvenile common carp ( Cyprinus carpio L.) held in either static water (tank rested, TR 16) or exercised in a flume at 2.5–3.2 body lengths s − 1 for 18 h a day (exercised, E 16). Relative to the start of the experiment (TR 0), the TR 16 group showed a 31% increase in body mass (specific growth rate, 1.57% d − 1 ), whereas there was no net change in the E 16 group. There was, however, a significant exercise-induced hypertrophy of slow muscle fibres with average fibre cross-sectional area ( F CSA) increasing by 35% in the E 16 group, compared with 11% in the TR 16 group. In contrast, F CSA of fast muscle fibres increased by 34% in the TR 16 group compared to just 18% in the E 16 group. The relative concentrations and subcellular localisation of proteins hypothesised to play a role in the regulation of muscle growth were measured. MyoD concentration was similar in the TR 0, TR 16 and E 16 groups in both slow and fast muscle. However, there was a small (5%–10%) but statistically significant increase in nuclear localisation of MyoD in those groups showing a significant increase in F CSA over the time course of the experiment. PCNA concentration was 31% and 12% higher in the TR 16 than in either the TR 0 or E 16 groups for slow and fast muscle, respectively. Exercise resulted in a ∼10% increase in nuclear factor of T-cells (NFAT2) concentration in slow muscle but no change in NFAT2 localisation. Calcineurin B concentration was similar in tank rested and exercised groups. The results do not support a major role for the calcineurin-signalling pathway in the regulation of muscle hypertrophy in the common carp.

Heritability estimates for growth-related traits using microsatellite parentage assignment in juvenile common carp ( Cyprinus carpio L.)

Common carp is one of the leading species in world aquaculture, but selective breeding for growth rate has not been actively pursued in this species after unsuccessful selection experiments. We estimated heritability for growth-related traits at 8 weeks of age in Hungarian Synthetic Mirror carp at Vodnany (Czech Republic). Parentage assignment with eight microsatellite markers was used in a full factorial cross of 10 dams×24 sires. Out of 550 offspring, 95.3% could be assigned to a single parental pair. Animal model heritability estimates were 0.33±0.08 for weight 0.33±0.07 for length and 0.37±0.07 for Fulton's condition factor ( K). Maternal effects and dominance were not significantly different from zero. The genetic correlation between weight and length was 0.98, and negative correlations were found between K and length (−0.38) and K and weight (−0.17). It is concluded that selective breeding for increased weight gain can be successful in juvenile carp, using indirect selection for length. However, the facts that heritability was estimated at 8 weeks of age and not at harvest weight, as well as a possible amplification of additive variance by competition, are limitations to the applicability of the present results.

Quantification of common carp (Cyprinus carpio) IGF-I and IGF-II mRNA by real-time PCR: differential regulation of expression by GH.

IGFs are potent mitogens for many different cell types and play important roles in growth and development. A multitude of regulatory factors modulate the expression of IGFs. In some teleosts, liver IGF-I expression has been demonstrated to depend on the presence of GH. However, the GH dependence of IGF-II expression in teleosts is controversial. Moreover, most IGF expression studies in bony fish have been focused on the liver, and information on extrahepatic tIssues are conflicting and inconsistent. This is partly due to the fact that the traditional methods of mRNA measurement such as Northern blot and RT-PCR are not sensitive enough to detect changes in IGF levels in extrahepatic tIssues because of the low levels of IGFs in these tIssues. In addition, there have been few studies on the IGF system of non-salmonid teleosts. Our laboratory has thus begun such studies on a local tropical fast-growing fish, the common carp (Cyprinus carpio). In this study, real-time quantitative PCR assays were developed for the accurate measurement of IGF-I and IGF-II mRNA levels in common carp tIssues. This quantitative method was based on the measurement of a fluorescent labeled probe, which was cleaved by Taq polymerase during PCR by the 5'-->3' nuclease activity. The signal generated was directly proportional to the starting copy number of the target molecules in the sample. Hence, it was possible to detect and quantify the mRNA levels of both IGF-I and IGF-II reliably in very small amounts of tIssues obtained from juvenile common carp. Using these assays, the expression pattern of IGF-I and IGF-II in various common carp tIssues was studied, and their differential response to GH stimulation was also investigated.

Effect of Deltamethrin on Haematological Indices of Common Carp (Cyprinus carpio L.)

Svobodova Z., V. Luskova, J. Drastichova, M. Svoboda, V. Ilabek: Effect of Deltamethrin on Haematological Indices of Common Carp (Cyprinus carpio L.). Acta Vet. Brno 2003, 72: 79-85. The aim of this study was to assess the effect of deltamethrin [(S)- a -cyano-3-phenoxybenzyl (1R,3R)-3-(2,2-dibromvinyl)-2,2-dimethylcyclo-propancarboxylate] on common carp (Cyprinus carpio L.). The effect was assessed on the basis of the results of acute toxicity tests and on the comparison of results of haematological examination of a control and an experimental group exposed to Decis flow 2.5 pesticide preparation (active substance 25 g.l -1 of deltamethrin). The acute semistatical toxicity test lasting 96 h was performed on common carp juveniles. The 96hLC50 value of Decis flow 2.5 was 0.058 mg.l -1 . Examination of erythrocyte and leukocyte profile was performed on 15 control and 28 experimental specimens of one-to-two-year-old common carp after 96 h of exposure to Decis flow 2.5 in a concentration of 0.13 mg.l -1 . The experimental group showed significantly lower values (p < 0.01) of erythrocyte count (RBC), haemoglobin content (Hb), haematocrit (PCV) and plasma total protein (TP) compared to the control group. Values of MCV, MCH and MCHC were comparable in the two groups during the study. Also, the leukocyte count (Leuko) and relative and absolute count of lymphocytes, monocytes, neutrophil granulocytes and their developmental forms were comparable in the two groups. The deltamethrin-based Decis flow 2.5 pesticide preparation was classified among substances strongly toxic for fish. Changes in the erythrocyte profile and plasma total protein after exposure to deltamethrin-based preparation may be referred to possible disruption of haematopoiesis and proteosynthesis.

Evaluation of Propeller-Induced Mortality on Early Life Stages of Selected Fish Species

Abstract The mortality of ichthyoplankton entrained through a scale model of a towboat propeller was evaluated in a large (>2 million L) circulating water channel. Five species of fish (larval shovelnose sturgeon Scaphirhynchus platorynchus, larval lake sturgeon Acipenser fulvescens, the larvae and eggs of paddlefish Polyodon spathula, larval blue sucker Cycleptus elongatus, and juvenile common carp Cyprinus carpio) were tested. Replicate groups of individuals were subjected to one or more shear stress levels (634, 1,613, 3,058, and 4,743 dynes/cm2 (1 dyne = the force that would give a free mass of 1 g an acceleration of 1 cm/s2). Mortality was a linear function of shear stress for all species and life stages. Paddlefish eggs and common carp juveniles were more resistant to shear stress than all larval fish. Smaller larvae (lake sturgeon and blue suckers) experienced higher mortalities (>75%) than larger larvae (shovelnose sturgeon and paddlefish). The conditional mortality (i.e., treatment less control m...

Cortisol affects testicular development in male common carp, Cyprinus carpio L., but not via an effect on LH secretion

Previous work showed that prolonged elevated cortisol levels, implicated in the stress adaptation, inhibits testicular pubertal development in male common carp, as well as an impairment of the synthesis of the 11-oxygenated androgens. This may be a direct effect of cortisol on the testis or via the gonadotropin secretion by the pituitary. The aim of the present study was to investigate whether cortisol has an effect on pituitary LH secretion. Juvenile common carp were fed with cortisol containing food pellets. Elevated cortisol levels blocked the increase in testosterone levels and pituitary LH content, but induced higher plasma LH levels at the end of puberty. The in vitro LH release capacity was correlated to the pituitary LH content. At the final stage of pubertal development, when a significant difference in pituitary LH content was observed, sGnRHa-induced LH release was also decreased. Testosterone has been shown to induce development of pituitary gonadotrophs, leading to an increase in LH content and GnRH-inducible LH release, but a decrease in plasma LH levels. We observed decreased plasma testosterone levels as a consequence of prolonged cortisol treatment. It is hypothesised that cortisol inhibits the testicular testosterone secretion and thereby, prevents LH storage. In vitro, this leads to a reduced GnRH-inducible LH release, but in vivo to increased LH plasma levels. It is very unlikely that the impaired testicular development is due to an effect of cortisol on LH secretion.

Effects of variable feed allowance with constant energy and ratio of energy to protein in a diet for constant protein input on the growth of common carp Cyprinus carpio L.

An 11-week feeding trial was conducted to evaluate the effects of dietary protein and/or energy levels on growth, feed efficiency and proximate composition of juvenile (average weight: 21.5 g) common carp (Cyprinus carpio L.) fed various diets based on constant daily protein input. Five experimental diets were prepared. One group of diets (diets 1, 2 and 3) contained three crude protein (P) levels (35%, 40% and 45%) with a constant gross energy (GE) of 3.8 kcal g−1 diet. The second group of diets (diets 4 and 5) were formulated to contain a GE of 4.3 or 4.9 kcal g−1 diet and 40% or 45% protein levels, respectively, where GE/P was constant at 10.8 kcal g−1 protein. Fish receiving diet 1 served as the control; they were hand-fed to visual satiety. Feed allowance for diets 2 and 4 was 87.5% of the control. Feed allowance for fish receiving diets 3 and 5 was 77.8% of the control. Thus, all tanks received the same daily protein input. When gross energy in the diets was constant, 3.8 kcal g−1 diet, weight gain of fish fed diet 2 at 87.5% satiation was significantly higher than that of fish fed diet 3 at 77.8% of satiation. When the GE/P in the diets was constant, 10.8 kcal g−1 protein, weight gain of fish fed diet 1 was significantly higher than that of fish fed diet 5 at 77.8% satiation. The feed efficiency ratio (FER) for diets 2–5 was significantly higher than for diet 1 at constant GE and GE/P, and this improved linearly as dietary protein levels increased. The protein efficiency ratio (PER) for diet 2 was significantly higher than for diet 3 at constant GE. However, PER was not significantly different at constant GE/P. Protein retention of fish fed diet 2 was significantly higher than that of fish fed diet 3 at constant GE. Protein retention of fish linearly decreased at constant GE/P. The energy efficiency ratios (EER) for diets 2 and 3 were significantly higher than for diet 1 at constant GE. Moisture and protein contents of the whole body of fish were not significantly different at constant GE, but they decreased linearly at constant GE/P. The lipid content of fish fed diet 1 was significantly lower than that of fish fed diet 2 at constant GE, and body lipid content linearly increased at constant GE/P. These results indicate that growth and feed efficiency for common carp fed a 40% protein diet with 3.8 kcal g−1 diet GE at 87.5% satiation rate was superior to those for the fish fed either a 35% protein diet with 3.8 kcal g−1 diet GE at 100% satiation rate or a 45% protein diet with either a 3.8 or 4.9 kcal g−1 diet GE at 77.8% satiation rate.

The Effect of Diazinon on Haematological Indices of Common Carp (Cyprinus carpio L.)

Svoboda M., V. Luskova, J. Drastichova, V. Ilabek: The Effect of Diazinon on Haematological Indices of Common Carp (Cyprinus carpio L). Acta Vet. Brno 2001, 70: 457-465. The goal was to assess an effect of diazinon [0,0-diethyl 0-(2-isopropyl-6-methylpyrimidin-4yl) phosphorothioate] on common carp (Cyprinus carpio L.). The effect was assessed based on results of acute toxicity tests and on a comparison of results of haematological examination of a control and an experimental group exposed to Basudin 600 EW pesticide preparation (active substance 600 g.l -1 of diazinon). The acute toxicity test lasting 96 h was performed semistatically on common carp juveniles. Examination of erythrocyte and leukocyte profile was performed on 15 control and 25 experimental specimens of one-to-two-year-old common carp after 96 h of exposure to Basudin 600 EW in concentration of 32.5 mg.l -1 . The 96hLC50 value of Basudin 600 EW for common carp juveniles was 26.7 mg.l-1. The experimental group of one- to two-year-old common carp showed significantly lower values (p < 0.01) of erythrocyte count (RBC), haemoglobin content (Hb) and haematocrit (PCV) compared to the control group. Values of MCV, MCH and MCHC were comparable in both groups during the study. In contrary, there was a significant decrease in leukocyte count (Leuko) (p < 0.01), as well as in both the relative and absolute lymphocyte count (p < 0.01) and a significant increase in both the relative and absolute count of developmental forms of neutrophile granulocytes: myelocytes (p < 0.01) and metamyelocytes (p < 0.05) in the experimental group. Relative and absolute count of monocytes and both the band- and segmented neutrophile granulocytes was comparable in both groups during the study. The diazinon-based Basudin 600 EW pesticide preparation was classified among harmful substances for fish. Changes in values of both the erythrocyte and leukocyte profile after exposure to diazinon-based preparation may be refered to disruption of haematopoiesis as well as to a decrease on non-specific immunity of the fish.

Chronic toxicity of nonylphenol and ethinylestradiol: haematological and histopathological effects in juvenile Common carp ( Cyprinus carpio)

In recent ecotoxicological research, there is an increasing concern about alkylphenolic industrial chemicals, such as nonylphenol (NP), because of their estrogenic properties. Data on the general fish toxicity of these wide spread aquatic pollutants are scarce. In order to evaluate sublethal toxic effects of environmentally relevant concentrations of NP, juvenile Common carp ( Cyprinus carpio) were exposed to NP concentrations ranging from 1 to 15 μg NP/l over a 70-day period. Classical toxicological endpoints, such as various haematological parameters and histopathological alterations were investigated. In a comprehensive protocol, besides NP-induced effects also alterations due to a treatment with the synthetic estrogen ethinylestradiol (EE2) were evaluated. After both the NP-exposure as well as the EE2-treatment, the predominant haematological finding was a severe anaemia. Histopathological alterations in the kidney, the liver and the spleen occurred exclusively after treatment with EE2, whereas NP-exposed fish did not show any tissue lesions. Depending on the haematological parameter examined, a NOEC between 1 and 5 μg NP/l could be established. From the present findings, it is assumed, that under field conditions, the NP-induced, general toxic effects, might outbalance the relatively weak estrogenic effects of this compound and possibly might disturb ecologically relevant processes such as fish reproduction.

Metal toxicity and metallothionein gene expression studies in common carp and tilapia

In Hong Kong, carp and tilapia are common in ponds and rivers. Tilapia is the dominant fish species found in contaminated rivers and estuarine regions. Heavy metal pollution is one of the major problems. Here we report the use of juvenile common carp and tilapia to study: (i) lethal concentrations of copper and zinc; and (ii) metallothionein (MT) mRNA levels in liver and gills of these fish after exposure to different concentrations of metals. For tilapia, the 96-h LC 50 values for copper and zinc were determined to be 1.52 and 24.3 ppm, respectively. However, for common carp, the 96-h LC 50 values of copper and zinc were found to be 50 and 17 ppm, respectively. This indicated that tilapia is a copper-resistant species while carp is sensitive to copper ions. Juvenile carp and tilapia were exposed to different sub-lethal concentrations of copper, zinc and cadmium for 3 weeks in the laboratory, to study MT gene expression. Our results showed that exposure of common carp to these metals did not induce MT mRNA in gill and liver tissues. However, exposure of tilapia to metal ions showed significant induction of MT mRNA in the same tissues. In conclusion, carp MT level is not a sensitive biomarker for monitoring metal pollution, and tilapia MT levels may be a better biomarker for monitoring metal contamination in local waters.

Effects of sublethal copper exposure on copper accumulation, food consumption, growth, energy stores, and nucleic acid content in common carp.

Juvenile common carp were exposed for 28 days to three different sublethal copper concentrations (0.20 microM, 0.55 microM, and 0.80 microM). Food consumption was monitored on a daily basis during the exposure period, while growth, copper accumulation, energy stores, and nucleic acid contents were assessed weekly. Copper exposure to 0. 80 microM affected both growth and feeding behavior in common carp. At 0.55 microM, growth was affected despite normal food consumption. Even at the lowest copper concentration (0.20 microM), metabolic demand for the fish increased, challenging the carp with an increased demand for food. Copper accumulation mainly occurred in the liver, reaching an equilibrium between uptake and excretion after 1 month of exposure. Substantial biochemical changes were observed at the two highest copper exposure concentrations, but the correlation between growth rate and RNA:DNA ratio was poor considering the substantial differences in growth rate. The use of the RNA:DNA ratio as a sensitive biomarker is questioned.

Partitioning and Bioaccumulation of Cadmium from the Sediment of Brackishwater Ponds in Sundarban, India

Sediment samples from 12 brackishwater ponds in Sundarban, India, showed cadmium (Cd) levels of 2.6-6.7 mg.kg·1• When these sediment samples were overlain with Cd-free water in the laboratory, Cd partitioned from the sediment into the water and reached concentrations of 0.08-0.54 mg-1·1• The extent of partitioning was not proportional to the amount of Cd in the sediment. The presence of common carp juveniles and tubificid worms did not influence the partitioning rate, but Cd concentrations in the water were significantly lower when these organisms were present. Both common carp juveniles and tubificid worms accumulated Cd, the fish more than the worms.

Estradiol Stimulates Growth Hormone Production in Female Goldfish

The effects of estradiol (E2) on growth hormone (GH) production was investigated in gonad-intact female goldfish. It was first necessary to generate a specific antibody for use in immunocytochemistry, Western, and dot-blot analyses of GH production. To accomplish this, grass carp GH (gcGH) cDNA was cloned by the reverse transcription polymerase chain reaction (RT-PCR) and expressed inEcherichia coliand a specific polyclonal antibody to recombinant gcGH was generated in the rabbit. In Western blot, the anti-gcGH antibody specifically immunoreacted with recombinant gcGH, purified natural common carp GH, and with a single 21.5-kDa GH form from pituitary extracts of grass carp, common carp, goldfish, and zebrafish but not salmon, trout, or tilapia. Intraperitoneal injection of the recombinant gcGH enhanced the growth rates of juvenile common carp demonstrating biological activity of this GH preparation. Electron microscopic studies showed that the anti-gcGH-I antibody specifically reacted with GH localized in the secretory granules of the goldfish somatotroph. Using anti-gcGH-I in a dot-blot assay, it was found thatin vivoimplantation of solid silastic pellets containing E2(100 μg/g body weight for 5 days) increased pituitary GH content by 150% in female goldfish. In a second, independent study employing a previously characterized anti-common carp GH antibody for radioimmunoassay, it was found that E2increased pituitary GH content by 170% and serum GH levels by approximately 350%. The E2-induced hypersecretion of GH and increase in pituitary GH levels was not associated with changes in steady-state pituitary GH mRNA levels, suggesting that this sex steroid may enhance GH synthesis at the posttranscriptional or translational level. Previous observations indicate that GH can stimulate ovarian E2production. The present results show that E2can in turn stimulate GH production, indicating the existence of a novel pituitary GH–ovarian feedback system in goldfish.

Central monoaminergic responses to salinity and temperature rises in common carp

Juvenile common carp, Cyprinus carpio, were exposed to increased levels of salinity (1 % NaCl) at 25 &deg;C and 30 &deg;C. Levels of the monoamine neurotransmitters dopamine (DA) and serotonin (5-HT) and their metabolites dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were determined in different brain parts. Whereas the elevated temperature only resulted in higher levels of the metabolites, increased salinity caused increased levels of DA and 5-HT as well. Increased levels appeared after the first day of exposure and most effects were further enhanced after 1 week in 1 % NaCl. Increases in DA and 5-HT levels were most pronounced in the hypothalamus, which is the major integrative centre controlling the release of hormones. Thus, one possible role of these changes in neurotransmitter metabolism could be to control the release of prolactin and cortisol, two major hormones involved in the regulation of ion homeostasis in teleosts.

Survey of Fishes from Rattlesnake Creek in Central Kansas

We collected 13 species of fishes at 10 sites in Rattlesnake Creek in Edwards, Stafford, and Rice counties, Kansas, during October 1993. In August 1995, a crew from Kansas Department of Wildlife and Parks sampled one site in Stafford County and captured 11 species. Historical collections in this stream included Arkansas darters (Etheostoma cragini), a threatened species in Kansas. None were taken in 1993, but they were captured in 1995. The alluvial aquifer of the lower reach of the stream is in contact with a geological formation that contributes chlorides to the surface water. Chloride values in October 1993 ranged from 10-39 mg/L in the upper portion of the creek to a maximum of 3140 mg/L in the lower reach. Concurrent with this change in water quality, a transition was noted in the fish communities from those dominated by adult red shiners (Cyprinella lutrensis) or juvenile common carp (Cyprinus carpio) in the upper reach to those dominated by adult plains killifish (Fundulus zebrinus) in the lower reach.

Brain monoamine levels and energy status in common carp ( Cyprinus carpio) after exposure to sublethal levels of copper

Serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) are two major monoamine neurotransmitters with a multitude of functions in the vertebrate brain. In fish, the 5-HT system has been shown to be sensitive to various forms of stress, but very few studies have examined the effects of toxic metals on these monoamine systems. Juvenile common carp were exposed to copper levels of 0.22, 0.34 and 0.84 μM during 1 week. In telencephalon, dose-dependent falls in 5-HT and DA levels were observed, with approximately 50% losses of these neurotransmitters at the highest copper concentration. Although less dramatic, falls were also seen in 5-HT and DA levels in hypothalamus and brain stem. No changes in 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite), AMP, ADP, ATP, adenylate energy charge or lactate levels were observed in brain. However, lactate levels in blood plasma increased with copper concentration. A significant copper accumulation only occurred in the liver, while no changes in brain or muscle were seen. It is concluded that copper exposure of common carp causes decreased brain 5-HT and DA levels, two neurotransmitters involved in, for example, feeding behaviour and locomotor control in fish. In fact, in telencephalon a fall in 5-HT levels was seen already at a copper concentration below that where food intake and movement were impaired.

Seasonal and Size-Related Changes in the Diet of Northern Pike from a Shallow Prairie Lake

ABSTRACT Food habits of northern pike (Esox lucius) were documented in Lake Thompson, a shallow, windswept, eutrophic lake in eastern South Dakota. The primary food items, assessed with the Relative Importance Index, eaten by northern pike were common carp (Cyprinus carpio), crappies (Pomoxis spp.), and fathead minnows (Pimephales promelas). Common carp were eaten in midsummer and winter. Crappies were eaten primarily in the winter. Fathead minnows were an important food source throughout the year. Macroinvertebrates were consumed by northern pike up to 600 mm throughout the open-water months. Northern pike in the smaller length groups (401–500 mm, 501–600 mm) ate primarily fathead minnows, juvenile common carp, and macroinvertebrates. Diets of larger northern pike consisted primarily of larger common carp, juvenile crappies, leopard frogs (Rana pipiens), and occasionally walleyes (Stizostedion vitreum).

Acute toxicity of selected organophosphorus pesticides to Cyprinus carpio and Barilius vagra

The acute toxicity of two organophosphorus (OP) pesticides, diazinon and malathion to Cyprinus carpio and Barilius vagra was determined. Mortalities and LC50-96 hr values for B. vagra and C. carpio were variable. Both juvenile common carp and B. vagra were extremely sensitive to diazinon. Adult B. vagra were more sensitive to malathion than were juvenile common carp.

The effect of malathion, diazinon, and various concentrations of zinc, copper, nickel, lead, iron, and mercury on fish.

Acute and chronic toxicity tests for malathion, diazinon, copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), nickel (Ni), and iron (Fe) were conducted. Mortalities of Barilius vagra and Cyprinus carpio (common carp) were variable but LC50-96 hr were similar for pesticides. Adult B. vagra seem to be more sensitive to malathion than juvenile carp. Both juvenile carp and adult B. vagra were extremely sensitive to diazinon. Long-term exposure to pesticides modified morphology and behavior. The LC50-96 values for Cu, Hg, and Pb were 0.3, 0.16, and 0.44, respectively, for smaller fish and 1.0, 0.77, and 1.33, respectively, for larger fish. Replicate LC50 values for Zn, Ni, and Fe were somewhat variable, and for these metals, the size of the fish seemed to affect response because LC50 values increased as fish size increased. Copper, Pb, Zn, and Fe residues following exposure to sublethal concentrations of these metals for 15 d were significantly greater in whole juvenile common carp than in controls.

Magnesium status in freshwater fish, common carp (Cyprinus carpio, L.) and the dietary protein-magnesium interaction

Common carp juveniles were fed for 9 weeks one of the eight semipurified diets containing graded levels of magnesium, 0.08, 0.6, 1.1, 3, 2 g Mg kg(-1) and 25 or 44% protein.Fish growth and feed utilization were significantly affected by both Mg and protein levels in the diets. Significant interaction between these two studied variables existed in relation to the fish performance as well as to mean deposition rate of several minerals in common carp body. The fish fed diets containing 0.08 g Mg kg(-1) had reduced growth and developed deficiency signs such as muscle flaccidity and skin hemorrhages.Results indicated that a minimum Mg level of 0.6 g Mg kg(-1) was required to elevate plasma and bone magnesium content and to reduce the whole body Ca concentration (hypercalcinosis symptom). Further increase of dietary Mg up to 3.2 g Mg kg(-1) improved growth rate of fish insignificantly, but the deposition rate of dietary Mg fell to as low as 7.4 and 10.7 percent in low- and high-protein diet fed fish, respectively. In Mg-deficient fish, considerable amount of magnesium was absorbed via extra-oral routes, however, this way of the covering magnesium need becomes insufficient in fast growing fish.