Mirror Carp Research Articles

Dietary modulation of immune response and related gene expression profiles in mirror carp (Cyprinus carpio) using selected exotic feed ingredients

An investigation was conducted to evaluate the effect of feeding selected exotic ingredients on immune responses and expression of immune related genes in mirror carp (Cyprinus carpio). Fish were fed diets for a total of 56days. Fishmeal served as the main protein source in the control diet and two experimental diets consisted of fishmeal fixed at 34% provision of protein and the remaining 66% protein was provided either by earthworm meal (EW diet) or a combination of whey protein concentrate (8%) and casein (58%) (WPC diet). At the start of the trial fish were injected intraperitoneally with Aeromonas hydrophila bacterin and samples of carp blood were taken for gene expression, haematological and serological analysis. Compared to fish fed fishmeal, a significant increase in mRNA expression of the pro-inflammatory cytokines IL-1β (24h post injection) and TNFα (at 12h and 48h post injection) was observed in fish fed EW. Moreover a similar trend was observed for complement 3 (C3) gene, where fish fed EW showed significant elevations in mRNA expression values at both 12 and 48h post injection compared to control fed fish. In contrast, fish fed WPC showed a significant decrease in C3 and TNF-α mRNA expression compared to fish fed fishmeal (48 h post injection). Fish fed EW and WPC showed a significant increase in peripheral leukocyte levels compared to fish fed fishmeal 14d post injection. Fish fed fishmeal presented significantly higher circulatory IgM levels at 7d post injection compared to fish fed EW and WPC. In contrast, fish fed EW and WPC showed a significant increase in IgM levels at 28d post injection. The present study shows an up-regulation of all immune related genes in fish fed EW, compared to fish fed fish meal, which is indicative of an acute inflammatory response. In contrast it appears feeding WPC has an immunosuppressive effect towards TNFα and C3 expression in carp blood. This may be offset by the fact that feeding WPC to carp appears to aid in the increased production of circulatory IgM and leukocyte levels compared to fishmeal fed fish.

Genomic and expression analysis of a solute carrier protein (CcSLC25a5) gene from Cyprinus carpio Linnaeus

Using the Genefishing method, we identified seven potential regulatory genes involved in the process of scale morphogenesis in fishes. We further characterized a novel solute carrier protein gene (CcSLC), from the common carp which is differentially expressed in mirror carp and Jianli. The ORF encodes a peptide of 298 amino acids with a molecular mass of 31.5 kDa and a theoretical isoelectric point of 7.49. ScanProsite analysis indicated that it is a putative solute carrier protein that contains a substrate binding site. CcSLC was detected in carp embryos by in situ hybridization in the 70%-epiboly, 6-somite, and 14-somite embryonic stages. Gene expression stopped at the long pec stage. However, CcSLC25a5 was re-expressed during the initiation of scale formation in the regions that were scale covered. These findings provide novel insights into the features of early carp embryo and scale development.

Effects of a dietary β-(1,3)(1,6)-D-glucan supplementation on intestinal microbial communities and intestinal ultrastructure of mirror carp (Cyprinus carpio L.)

To assess the effects of dietary Saccharomyces cerevisiae β-(1,3)(1,6)-D-glucan supplementation (MacroGard(®)) on mirror carp (Cyprinus carpio L.) intestinal microbiota and ultrastructure of the enterocyte apical brush border. Carp were fed either a control diet or diets supplemented with 0.1, 1 or 2% w/w MacroGard(®). Culture-dependent microbiology revealed that aerobic heterotrophic bacterial levels were unaffected by dietary MacroGard(®) after 2 and 4 weeks. No effects were observed on the allochthonous lactic acid bacteria (LAB) populations at either time point; however, reduced autochthonous LAB populations were observed at week 4. PCR-DGGE confirmed these findings through a reduction in the abundance of autochthonous Lactococcus sp. and Vagococcus sp. in MacroGard(®)--fed fish compared with the control-fed fish. Overall, sequence analysis detected microbiota belonging to the phyla Proteobacteria, Firmicutes, Fusobacteria and unidentified uncultured bacteria. DGGE analyses also revealed that dietary MacroGard(®) reduced the number of observed taxonomical units (OTUs) and the species richness of the allochthonous microbiota after 2 weeks, but not after 4 weeks. In contrast, dietary MacroGard(®) reduced the number of OTUs, the species richness and diversity of the autochthonous microbiota after 2 weeks, and those parameters remained reduced after 4 weeks. Transmission electron microscopy revealed that intestinal microvilli length and density were significantly increased after 4 weeks in fish fed diets supplemented with 1% MacroGard(®). This study indicates that dietary MacroGard(®) supplementation modulates intestinal microbial communities of mirror carp and influences the morphology of the apical brush border. To the authors' knowledge, this is the first study to investigate the effects of β-(1,3)(1,6)-D-glucans on fish gut microbial communities, using culture-independent methods, and the ultrastructure of the apical brush border of the enterocytes in fish. This prebiotic-type effect may help to explain the mechanisms in which β-glucans provide benefits when fed to fish.

Quantitative trait loci analysis for body weight and standard length in mirror carp

Body weight and standard length traits are complex and important economic traits,and are also targets for selective animal breeding.Our objective was to identify QTL associated with body weight(BW) and standard length(SL) traits.We conducted a whole genome scan on 190 progeny from a full-sib family using 940 microsa-tellite markers.We conducted half-sib mapping using GridQTL software.We obtained 8 QTL distributed across 5 linkage groups(LG) during sire-based QTL analysis.For BW,5 QTL were identified,of which 1 QTL occurred at the 95% genome-wide level,and was located at LG26.The remaining 4 QTL were at the 95% chromosome-wide level,explaining 12.5%–32.6% of phenotypic variance.For SL,3 QTL overlapped with the BW QTL intervals.One QTL was identified at the 99% genome-wide level,and 2 QTL were at the 95% chromosome-wide level,ex-plaining 18.4%–40.9% of phenotypic variance.During dam-based QTL analysis,we identified 11 QTL that were distributed across 7 LGs.Six QTL were associated with BW,of which one was at the 99% genome-wide level and was also located at LG26.Two QTL were identified at the 99% chromosome-wide level,leaving 3 QTL at the 95% chromosome-wide level,accounting for 15.7%–37.6% of phenotypic variance.For SL,5 QTL were identified,of which 4 were the same marker or had a similar confidence interval with BW.Among these,1 QTL was identified at the 99% genome-wide level,1 QTL was at the 99% chromosome-wide level,and 3 QTL were at the 95% chro-mosome-wide level,explaining 16.7%–39.5% of phenotypic variance.Our results suggest that the most significant QTL maps to LG26 and is significant at the genome-wide level in both the sire and the dam-based analyses.The minimum confidence interval was only 3 cM,which can be used during molecular marker assisted selection(MAS) in mirror carp.Our results provide a useful reference for further candidate gene research and MAS in mirror carp.

Screening and body correlation analysis of microsatellite markers related to intermuscular bone number in common carp (Cyprinus carpio)

In this study, 149 polymorphic markers were screened from 200 microsatellite markers. From a family of mirror carp, which included 107 individuals. All samples were analyzed for body correlation, and intermuscular bone number was tested using the General Linear Model (GLM) single marker regression. Determination of the threshold values by 10,000 permutation tests showed that eight markers had significant correlation (P<0.05), in which HLJ3086, HLJ3642 and HLJ3515 had very significant correlation with intermuscular bone number (P<0.01). In addition, the genotypes of the captured correlative loci were determined by Duncan's test using SPSS17.0 software. Markers were used to screen the protein and nucleotide database in the National Center for Biotechnology Information (NCBI). Blasting results showed that HLJ2891 was highly correlated (92%) with latrophilin-2-like and HLJ3515 was highly correlated (81%) with serine/threonine-protein kinase 32B-like of zebrafish. These functional markers and genotypes may provide an efficient basis for marker-assisted selection of intermuscular bone number in mirror carp.

The primary culture of mirror carp snout and caudal fin tissues and the isolation of Koi herpesvirus

The explosive Koi herpesvirus (KHV) epidemic has caused the deaths of a large number of carp and carp variants and has produced serious economic losses. The mirror carp (Cyprinus carpio var. specularis) exhibits strong environmental adaptability and its primary cells can be used to isolate KHV. This study utilized the tissue explant method to systematically investigate primary cell culture conditions for mirror carp snout and caudal fin tissues. We demonstrated that cells from these two tissue types had strong adaptability, and when cultured in Medium 199 (M199) containing 20% serum at 26 to 30°C, the cells from the snout and caudal fin tissues exhibited the fastest egress and proliferation. Inoculation of these two cell types with KHV-infected fish kidney tissues produced typical cytopathic effects; additionally, identification by electron microscopy, and PCR indicated that KHV could be isolated from both cell types.

Effects of dietary β‐(1,3)(1,6)‐D‐glucan supplementation on growth performance, intestinal morphology and haemato‐immunological profile of mirror carp (Cyprinus carpio L.)

In recent years, aquaculture research has focused on probiotics, prebiotics, and β-glucans, in order to improve health status and growth performance. Information regarding the effects of β-glucan on growth performance and intestinal immunity of mirror carp (Cyprinus carpio L.) is scarce. An experiment was therefore conducted to investigate the effects of a yeast β-glucan preparation (MacroGard(®) ) on growth performance, intestinal morphology and haemato-immunological indices of mirror carp. Carp (initial weight 11.1 ± 0.0 g) were fed highly purified diets supplemented with 0% (control), 0.1%, 1% or 2% MacroGard(®) for 8 weeks. Fish fed diets containing 1% and 2% MacroGard(®) showed significant improvements in weight gain, specific growth rate and feed conversion ratio compared to fish fed both the control and the 0.1% MacroGard(®) containing diet. Histological appraisal of the intestine showed a significantly higher infiltration of leucocytes into the epithelial layer of fish fed diets supplemented with 1% and 2% MacroGard(®) in the anterior intestine compared to fish fed the control and 0.1% MacroGard(®) diet. This effect was not observed in the posterior intestine. There were no significant differences in the intestinal absorptive surface area and number of goblet cells in either intestinal region. At the end of the experiment, the haematological status of the fish was examined. Compared to control fed fish, the haematocrit value was significantly elevated in fish fed the 2% MacroGard(®) diet. Furthermore, the blood monocyte fraction was significantly higher in fish fed the 1% and 2% MacroGard(®) diets. No significant changes were observed in the other blood parameters assessed. The present study shows that high dietary β-glucan inclusion increases growth performance without detrimental effects on the health indicators assessed. Increased intraepithelial leucocytes in the anterior intestine may indicate a localized immune response; no detrimental effects on intestinal morphology were observed.

Growth Performance of Mirror Carp (Cyprinus carpio var. specularis, Lacepède, 1803) Fry Fed with Varying Protein Content Feeds

An experiment was conducted in aquaria for seven weeks to examine the effect of varying dietary protein level on growth, FCR (food conversion ratio) and survival of mirror carp fry. Similar weight (2.29 ± 0.08g) and length (4.21 ± 0.05 cm) of mirror carp fry were stocked in the aquaria (1 fry/L) and fed laboratory prepared feeds containing 25% (T1), 30% (T2), 35% (T3), 40% (T4), and 45% (T5) protein. In terms of growth and FCR, diet containing 30% protein performed significantly (p&lt;0.01) better than those of other tested diets. Survival rate, on the other hand, dropped significantly (p&lt;0.01) when the stocks were fed diets containing over 30% protein. These findings suggest that about 30% protein in diet appears to be sufficient for obtaining optimum growth of mirror carp fry.DOI: http://dx.doi.org/10.3126/on.v10i1.7747

Comparison of growth and reproduction of mirror carp and scaled carp introduced into Gelingüllü Reservoir, Yozgat, Turkey

Carp have been translocated and introduced outside of their natural range in many countries. In Turkey, mirror carp (a warm-water fish) has generally been introduced into man-made reservoirs for fishery management, regardless of geographic location and climatic conditions. During the previous decade, controversy has arisen concerning the adaptation and spawning of carp, and the success of such introduction practices in Central Anatolia, which is characterized by typical cold continental weather conditions. Concurrently, based on some irregular observations, scaled carp was reintroduced as an alternative to mirror carp. Long-term monitoring studies on the growth and reproduction of mirror carp and scaled carp introduced into reservoirs are necessary for effective fishery management. This study aimed to compare the growth and reproduction of mirror carp and scaled carp populations in Gelingüllü Reservoir. A total of 796 mirror carp and 285 scaled carp were caught between June 2002 and July 2005. Scaled carp reached up to 61.9 cm in fork length (FL) at age 8+ whereas mirror carp could reach to a maximum of 71.5 cm in FL at age 9+. The data show that mirror carp had a better growth rate and higher fecundity than scaled carp. Introduction of mirror carp may be recommended for fishery management applications under continental climate conditions.

A novel 79-bp insertion/deletion polymorphism in 3′-flanking region ofIGF-Igene is associated with growth-related traits in common carp (Cyprinus carpioL.)

Insulin-like growth factor-I (IGF-I) participates in the modulation of the cellular development, differentiation and proliferation in various vertebrate tissues. Therefore, variations in IGF-I gene are good candidates as growth regulators. In this study, a novel 79-bp insertion/deletion (I/D) polymorphism was identified in 3′-flanking region of IGF-I gene by polymerase chain reaction (PCR) and sequencing approaches in common carp Cyprinus carpio. To gain insight into the association of the 79-bp I/D polymorphism with growth-related traits, a total of 747 individuals from Heilongjiang carp Cyprinus cario haematopterus (YL) (n = 263), selective line of German mirror carp Cyprinus carpio L. mirror (JL) (n = 229), and cold-resistance line of Hebao red carp Cyprinus carpio var. wuyuanensis (HL) (n = 255) were genotyped. The DD genotype of the polymorphism was significantly associated with higher body length (135), body weight (325, 385, and 445 days), net weight (445 days) and lower overwintering body loss rate in JL. In addition, in pooled population (YL+JL+HL), fish with DD genotype also showed significantly higher body weight (445 days) and net weight (445 days) than those with II genotype. Taken together, these results suggest that the novel polymorphism in IGF-I gene could be considered as a potential genetic marker for selection of growth performance in common carp.

The Quality Changes of Songpu Mirror Carp (Cyprinus carpio ) during Partial Freezing and Chilled Storage

In order to understand the effects of partial freezing (at −3C) and chilled (at 3C) storage on quality of Songpu mirror carp (Cyprinus carpio) fillets, total aerobic count (TAC), K value, adenosine triphosphate and related compounds, total volatile base nitrogen (TVB-N), drip loss, electric conductivity (EC), and sensory scores of Songpu mirror carp fillets were investigated. According to sensory scores, shelf life of fillets at 3C and −3C were 9 days and 21 days, respectively. TAC of fillets was 7.12 and 3.70 log cfu/g at 3 and −3C on the ninth day, respectively. The TVB-N of fillets was 13.72% on the sixth day at 3C and 13.98% on the 30th day at −3C. The EC of fillets under both conditions showed no significant difference (P > 0.05). Additionally, K value was not suitable for evaluating freshness changes of Songpu mirror carp. Partial freezing could extend shelf life more effectively than chilled storage. Practical Applications The study investigated the effects of partial freezing and chilled storage on the quality of Songpu mirror carp fillets. Partial freezing storage could extend 2.3 times of shelf life of Songpu mirror carp compared with chilled storage. If shorter shelf life of up to 9 days for Songpu mirror carp is required, chilled storage was better than partial freezing storage. At the requirement of 9–21 days of storage, partial freezing was favorable.

Impacts of domestication on angling vulnerability of common carp, Cyprinus carpio: the role of learning, foraging behaviour and food preferences

AbstractDomestication in fish selection increases vulnerability to angling. Two common garden‐reared genotypes of common carp, Cyprinus carpio L., differing in degree of domestication (highly domesticated mirror carp and less domesticated scaled carp) were exposed to fishing in two environments (i.e. ponds and laboratory tanks) to quantify vulnerability to angling. Foraging behaviour and food preferences were quantified to explain variation in angling vulnerability in a mechanistic manner. Domesticated mirror carp were more vulnerable to angling gear than scaled carp in both environments, which was related to greater food intake and bolder‐foraging behaviour. Independent of genotype, catchability decreased and time until first capture increased over fishing time, indicating learned hook avoidance. No differences were observed in food preferences among genotypes, rendering bait‐selective feeding an unlikely explanation for differential vulnerability to angling. It was concluded that vulnerability to angling has a genetic basis in carp and that boldness plays a paramount role in explaining why more domesticated genotypes are more easily captured by angling.

Modelling quality changes in Songpu mirror carp (Cyprinus carpio) fillets stored at chilled temperatures: comparison between Arrhenius model and log‐logistic model

SummaryTo understand the quality changes in Songpu mirror carp (Cyprinus carpio) fillets during chilled storage, sensory score, total aerobic counts (TAC), total volatile basic nitrogen (TVB‐N) and electrical conductivity (EC) of the fillets stored at 270, 273, 276, 282 and 288 K were investigated. Furthermore, both Arrhenius model and log‐logistic model were established to predict the quality changes. The high regression coefficients (R2 &gt; 0.90) represented the acceptability of both Arrhenius model and log‐logistic model. Relative errors between predicted values and observed values were all within ±5% for models based on EC, within ± 25% for models based on TAC and TVB‐N (except the TVB‐N value on 9th and 15th day). The relative errors of sensory score were all within ±35% in the first 9 days. It is concluded that both Arrhenius model and log‐logistic model based on EC, TAC or TVB‐N can be applied in modelling quality changes in Songpu mirror carp fillets during storage within 270–288 K.

Genome-Wide SNP Discovery from Transcriptome of Four Common Carp Strains

BackgroundSingle nucleotide polymorphisms (SNPs) have been used as genetic marker for genome-wide association studies in many species. Gene-associated SNPs could offer sufficient coverage in trait related research and further more could themselves be causative SNPs for traits. Common carp (Cyprinus carpio) is one of the most important aquaculture species in the world accounting for nearly 14% of freshwater aquaculture production. There are various strains of common carp with different economic traits, however, the genetic mechanism underlying the different traits have not been elucidated yet. In this project, we identified a large number of gene-associated SNPs from four strains of common carp using next-generation sequencing.ResultsTranscriptome sequencing of four strains of common carp (mirror carp, purse red carp, Xingguo red carp, Yellow River carp) was performed with Solexa HiSeq2000 platform. De novo assembled transcriptome was used as reference for alignments, and SNP calling was done through BWA and SAMtools. A total of 712,042 Intra-strain SNPs were discovered in four strains, of which 483,276 SNPs for mirror carp, 486,629 SNPs for purse red carp, 478,028 SNPs for Xingguo red carp and 488,281 SNPs for Yellow River carp were discovered, respectively. Besides, 53,893 inter-SNPs were identified. Strain-specific SNPs of four strains were 53,938, 53,866, 48,701, 40,131 in mirror carp, purse red carp, Xingguo red carp and Yellow River carp, respectively. GO and KEGG pathway analysis were done to reveal strain-specific genes affected by strain-specific non-synonymous SNPs. Validation of selected SNPs revealed that 48% percent of SNPs (12 of 25) were tested to be true SNPs.ConclusionsTranscriptome analysis of common carp using RNA-Seq is a cost-effective way of generating numerous reads for SNP discovery. After validation of identified SNPs, these data will provide a solid base for SNP array designing and genome-wide association studies.

Studies on quantitative trait loci related to superoxide dismutase in mirror carp (Cyprinus carpioL.)

The F1 progeny from parents selected randomly for differences in performance traits from different families of mirror carp were used as a mapping panel. Linkage maps constructed using Join Map 4.0 software with 992 microsatellite polymorphic markers ultimately yielded 51 groups. Composite interval mapping (CIM) of superoxide dismutase (SOD) trait of three tissues (liver, anterior and posterior intestine) was conducted for quantitative trait loci (QTL) location using Map QTL 6.0 software. Results shows that seven QTLs significantly (P 85%). These results showed that it is highly probable that these QTLs are the main regions of SOD expression. The data also support the value of forward genetic studies on organism development and serve as a basis for selection.

Impact of Exotic Carps in the Polyculture with Indigenous Carps: Competition for Food

The fingerlings of indigenous carps such as catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala) with exotic carps such as silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis) and mirror carp (Cyprinus carpio) were cultured together in a fish pond at Bangladesh Agricultural University, Mymensingh, in order to determine the food electivity, dietary overlap and food competition among indigenous major carps and exotic carps. Phytoplankton (Chlorophyceae, Cyanophyceae), zooplankton (rotifers) were the dominant groups in the cultured pond. Chlorophyceae was dominant in the diet of rohu. Chlorophyceae and rotifers were the preferred food of catla. Mrigal preferred phytoplankton than zooplankton. Rohu showed positive electivity for zooplankton. Silver carp consumed large quantity of phytoplankton and also preferred rotifers. Chlorophyceae was the dominant food group in the diet of bighead. Mirror carp also preferred plant food organisms dominated by Chlorophyceae. Bighead had positive trends towards phytoplankton. Both mrigal and mirror carp had positive electivity towards phytoplankton. The higher level of dietary overlap occurred between rohu and silver carp followed by between rohu and bighead carp and between catla and silver carp. The lowest level of dietary overlaps occurred between rohu and mirror carp.

Effect of partially replacing fish meal with honey locust seed (Gleditsia triacanthos) on growth, feed utilisation and body composition of mirror carp, Cyprinus carpio, fingerlings

Honey locust seed (HLS) (Gleditsia triacanthos) was evaluated as a partial replacement for fish meal (FM) in Cyprinus carpio fingerlings diets formulated to contain 38% crude protein, 13% lipid and 19.9 MJ/kg gross energy. An 60-day feeding trial was conducted in a recirculation system aquarium. HLS was included in the diets at different levels (0, 100, 200, 300 and 400 g raw and 100, 200, 300 and 400 g heat-treated for diets Control, Rw1, Rw2, Rw3, Rw4 Ht1, Ht2, Ht3 and Ht4, respectively) and FM was replaced by 0%, 5%, 10%, 15% and 20% of HLS (raw and heat-treated). The fish were handfed daily at of 3% of their body weight during the experiment. Diet had a significant effect on the growth performance. Heat treatment increased the inclusion level of HLS. There were no significant differences (P>0.05) among fish fed diets Control, Rw1, Rw2, HT1, HT2 and HT3 in terms of growth performance. Fish fed diets containing higher levels (>30%) of raw HLS seed had significantly lower whole body fat content. Raw and heat-treated HLS has potential as an alternative feed ingredient. These results show that up to 20% Raw HLS can be used to replace 10% of FM in diets for mirror carp. However, HLS should be heat-treated if inclusion rates are to exceed 20% of the diet.

Haemato-immunological and growth response of mirror carp (Cyprinus carpio) fed a tropical earthworm meal in experimental diets

An investigation was conducted to evaluate the effect of feeding a tropical earthworm meal (Perionyx escavatus) on the haemato-immunological response and growth performance of mirror carp (Cyprinus carpio). Fish were fed diets for a total of 88 days, fishmeal served as the main protein source in the control diet. Two remaining diets consisted of fishmeal fixed at 33.65% provision of protein and the remaining 66.35% protein was provided by soybean meal (SBM diet) or P. excavatus meal (EW diet). Compared to control and SBM fed fish (7.69 ± 0.28 and 5.92 ± 0.31 g/dl, respectively), a significant increase in haemoglobin was measured in EW fed fish (9.57 ± 0.24 g/dl). Consequently significant elevations were also observed in mean corpuscular haemoglobin (MCH; 79.13 ± 4.59 pg) and mean corpuscular haemoglobin concentration (MCHC; 22.69 ± 0.54 pg) in EW fed fish. On the contrary, compared to control and SBM fed carp total leukocyte levels (2.72 ± 0.17 and 3.10 ± 0.17 × 104/mm3, respectively) were significantly decreased in the EW group (2.15 ± 0.14 × 104/mm3). Moreover at day 14 and 21 post immunisation with bacterin isolated from Aeromonas hydrophila fish fed the EW diet displayed a significant reduction in respiratory burst activity (RBA) compared to control and SBM fed fish. After 60 days of feeding, fish fed EW diet showed a significant elevation in final body weight compared to fish fed a fishmeal based diet (control treatment) and fish fed a soybean meal based diet. Similar improvements were observed in feed utilisation efficiency. The present study shows that feeding P. excavatus meal to mirror carp decreases some aspects of the innate immune response, but at the same time gives rise to significant enhancement of growth and feed utilisation efficiency.

The Efficacy of Chromium as a Growth Enhancer for Mirror Carp (Cyprinus carpio L): An Integrated Study Using Biochemical, Genetic, and Histological Responses

A growth trial was conducted on juvenile mirror carp (Cyprinus carpio L.) for 8 weeks to compare the efficacy of three chromium (Cr) compounds (Cr chloride, Cr picolinate, and Cr yeast) at a level 0.5 mg/kg as a potential growth enhancer. In addition, a high level of Cr (2.0 mg/kg) as Cr chloride has also been added in parallel for comparison. All Cr fortified diets at a level 0.5 mg/kg produced superior growth for carp compared to the control group and the group fed the high level of Cr chloride (2.0 mg/kg). Metabolic indicators measured included two of the key liver enzymes (hexokinase, HK) and (glucose-6-phosphate dehydrogenase, G6PD) activity. The results validated the positive effect of Cr at a level 0.5 mg/kg on enzyme activity and carbohydrate utilization producing significantly better growth performance for mirror carp. The study also included measurement of DNA strand breaks in the erythrocytes using the comet assay which revealed significantly (P < 0.05) increased DNA damage in fish fed on high level of Cr chloride (2.0 mg/kg) but the other treatments were not significantly different (P > 0.05) from the control groups. The concentration of Cr in the liver, gut, and whole fish tissues increased with increasing dietary Cr supplementation. Overall, Cr supplementation at a level 0.5 mg/kg from different sources may affect growth performance in carp by activation of some key liver enzymes (HK and G6PD).

Determination of hypoxia and dietary copper mediated sub-lethal toxicity in carp, Cyprinus carpio, at different levels of biological organisation

Hypoxic events frequently occur in the aquatic environment in association with micro pollutants, including heavy metals. Only a few studies are however available on the uptake and biological responses of heavy metals under hypoxic conditions. To elucidate the phenomenon, mirror carp Cyprinus carpio L. (16.13–16.22g) were exposed chronically to dietary copper (Cu; 250 and 500mgkgdrywt.−1) for 30d under normoxic (8.25mgO2L−1) and hypoxic (∼3mgO2L−1) conditions and adopting an integrated approach, sub-lethal biomarker responses were determined at different levels of biological organisation. Level of oxidative DNA damage (as determined by modified Comet assay) showed strong significant difference following exposure to dietary Cu level under normoxic (1.6-fold) as well as under hypoxic condition at both Cu levels (2.1 and 2.5-folds respectively). Significant difference was also observed for haematological parameters (i.e. increased red and white blood cells, haematocrit value and haemoglobin concentration). Quantitative histology revealed alterations in tissues (i.e. liver and gills) for hypoxic and all dietary Cu treatment groups under both normoxic and hypoxic conditions suggesting a compensatory response to these organs (p<0.05). The order of Cu accumulation in tissues (as determined by ICP-OES) was liver>intestine>kidney>gill. Interestingly, SGR under both normoxic and hypoxic conditions reduced with elevating Cu levels (p=0.019). Overall, the results provide evidence for enhanced toxicological responses in fish following exposure to Cu either alone or in combination with hypoxic condition and lends support to the evolving viewpoint that many water quality guidelines should be revisited in terms of new ecotoxicological criteria.