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As a major component of the extracellular matrix, collagen has been used as a biomaterial for many purposes including tissue engineering. Commercial collagen derived from mammals is associated with a risk of prion diseases and religious restrictions, while fish-derived collagen can avoid such issues. In addition, fish-derived collagen is widely available and low-cost; however, it often suffers from poor thermal stability, which limits its biomedical application. In this study, collagen with a high thermal stability was successfully extracted from the swim bladder of silver carp (Hypophthalmichthys molitrix) (SCC). The results demonstrated that it was a type I collagen with high purity and well-preserved triple-helix structure. Amino acid composition assay showed that the amounts of threonine, methionine, isoleucine and phenylalanine in the collagen of swim bladder of silver carp were higher than those of bovine pericardium. After adding salt solution, swim-bladder-derived collagen could form fine and dense collagen fibers. In particular, SCC exhibited a higher thermal denaturation temperature (40.08 °C) compared with collagens from the swim bladder of grass carp (Ctenopharyngodon idellus) (GCC, 34.40 °C), bovine pericardium (BPC, 34.47 °C) and mouse tail (MTC, 37.11 °C). Furthermore, SCC also showed DPPH radical scavenging ability and reducing power. These results indicate that SCC presents a promising alternative source of mammalian collagen for pharmaceutical and biomedical applications.

Objectives: Recent studies on teleost fish evolution compare both molecular and morphological data to evaluate the taxonomic relationships. Therefore, the objective of our current study was to assess the potential of using scale microstructures for the taxonomic identification of two fish species, i.e., Hypophthalmichthys molitrix and Otolithes ruber. Materials and Methods: Eighty individuals of each carp species were collected from the Quetta fish market between August 2021 and January 2022. Then, microstructures, i.e., scale length and width, focus position, and the number of radii and ctenii of each fish scale obtained from five different fish-body regions, were examined. These measurements were used to compare the variations in scale microstructures between two fish species and may also help evaluate their potential utility in more accurate species identification and systematic classification. Results: The overall results reveal statistically significant variations (p < 0.05) between all examined scale microstructures, including the length or width of the scale, the focus position, and the number of radii or ctenii present on the fish scale, obtained from five body regions of two carp fish species. These results exhibit the potential utility of microstructure studies as a reliable approach for systematic identification. Therefore, our findings support the usage of fish scale microstructures as a valuable and non-invasive tool for taxonomic identification of any fish species. Moreover, this technique may specify the actual impact of these scale features as valuable tools for the conservation and management of endangered or threatened fish species. Conclusion: Our study provides a foundation for future systematic research and offers a satisfactory approach for non-invasive taxonomic identification.

Silver carp (Hypophthalmichthys molitrix) is one of the major species of freshwater fish in China. Modification of myofibrillar proteins induced by high pressure processing (HPP) has been investigated at pressures ranging from 200 to 500 MPa for 10 min at 20 °C. Influence of high pressure on conformational changes of myofibrils was studied by means of differential scanning calorimetry (DSC), surface hydrophobicity measurement, ultraviolet absorption spectra and second-derivative spectroscopy, intrinsic spectrofluorimetry, Raman spectroscopic analysis and circular dichroism (CD). DSC analyses revealed that the conformational stability of myofibrils is reduced to different extents when they are exposed to a pressure over 200 MPa. More sulfydryl groups as well as hydrophobic regions and amino acid residues which had ultraviolet absorbance had been found significantly after HPP (≥300 MPa). Changes in the Raman spectra were interpreted as the occurrence of secondary structural changes in pressure-induced myofibrillar proteins. CD analysis results demonstrated that α-helix was destroyed after processed at 400 MPa for 10 min. The results implicated that HPP can be used as a possible means of improving the functional properties for growing demand for healthier fish products.

To further prove the advantages of microwave-assisted water bath heating (MWH) in low-value fish processing, the effects of different heating methods (two heating stage method, high temperature section respectively using MWH1, MWH2, MWH3, WH—water heating, MH—microwave heating) on secondary and tertiary myosin structures, SDS-PAGE, surface morphology, scanning electron microscopy (SEM), and particle size distribution were compared and analyzed. The findings revealed that MH and MWH aided in the production of gel formations by promoting myosin aggregation. Myosin from silver carps demonstrated enhanced sulfhydryl group and surface hydrophobicity after MWH treatment, as well as a dense network structure. The distribution of micropores becomes more uniform when the microwave time is increased. Actually, the total effect of microwave time on myosin is not substantially different. The correlation between particle size distribution and protein aggregation was also studied, in terms of time savings, the MWH of short microwave action is preferable since it not only promotes myosin aggregation but also avoids the drawbacks of a rapid warming rate. These discoveries give a theoretical foundation for understanding silver carp myosin under microwave modification, which is critical in the food industry.

Silver carp (Hypophthalmichthys molitrix) is a potential source for making surimi products. However, it has the disadvantages of bony structures, high level of cathepsines and muddy off-odor which is mainly caused by geosmin (GEO) and 2-methylisoborneol (MIB). These disadvantages make the conventional water washing process of surimi inefficient (low protein recovery rate, and high residual muddy off-odor). Thus, the effect of the pH-shifting process (acid-isolating process and alkali-isolating process) on the cathepsins activity, GEO content, MIB content, and gelling properties of the isolated proteins (IPs) was investigated, comparing it with surimi obtained through the conventional cold water washing process (WM). The alkali-isolating process greatly boosted the protein recovery rate from 28.8% to 40.9% (p < 0.05). In addition, it removed 84% GEO and 90% MIB. The acid-isolating process removed about 77% GEO and 83% MIB. The acid-isolated protein (AC) displayed the lowest elastic modulus (G′), the highest TCA-peptide content (90.89 ± 4.65 mg/g) and the highest cathepsin L activity (65.43 ± 4.91 U/g). The AC modori (60 °C for 30 min) gel also demonstrated the lowest breaking force (226.2 ± 19.5 g) and breaking deformation (8.3 ± 0.4 mm), indicating that proteolysis caused by the cathepsin deteriorated the gel quality of AC. The setting (40 °C for 30 min) considerably increased the breaking force (386.4 ± 15.7 g) and breaking deformation (11.6 ± 0.2 mm) of the gel made from the alkali-isolated protein (AK) (p < 0.05). In AC and AK gel, a clearly visible cross-linking protein band with a molecular weight greater than MHC was seen, demonstrating the presence of endogenous trans-glutaminase (TGase) activity, that improved the gel quality of AK. In conclusion, the alkali-isolating process was an effective alternative method for making water-washed surimi from silver carp.

To investigate the effects of different raising environments on the flesh quality, the study set up three groups of silver carp (Hypophthalmichthys molitrix), that is, pond-farmed; short-term stocked; and ranched, grown in a natural water ranch. This study compared the differences in muscle proximate composition and amino acid composition among three groups. The results showed that there was no difference between the ranched and the stocked groups in content of crude protein, ash, total amino acids (TAA), essential amino acids (EAA), and umami-flavored amino acids (UAA), with both groups being significantly higher than the farmed group. This shows that, in terms of flesh quality, the stocked group was closer to the ranched group and better than the farmed group after being stocked in natural water for 30 days. The results suggest that the flesh quality of farmed fish was improved by short-term stocking in natural water. To elucidate the reasons of flesh quality change in the stocked group, this study compared the food composition and intestinal digestive enzyme activity in three groups, demonstrating that the ranched and stocked groups had similar food composition, with their detritus proportion lower than that of the farmed group, consuming easily digestible phytoplankton diatoms rich in amino acids and fatty acids. No significant difference was seen between the ranched group and the stocked group, for which amylase, lipase, and trypsin activities were lower than that of the farmed group. It is hypothesized that differences in environmental and food composition resulted in lower digestive enzyme activity in the ranched group and the stocked group. In summary, the short-term stocking of farmed fish in a natural water ranch can effectively improve the nutrient content, quality and flavor, and promote value of fish products.

The effectiveness of chemical compounds for marking hard tissues in juvenile silver carp (Hypophthalmichthys molitrix) is not well known. We analyzed the use of alizarin complexone (ALC) as a fluorescent marker to mark the various hard structures of juvenile silver carp. Experimental fish (~2 months old) were randomly assigned to either control or marking groups, which were immersed in 0 or 100 mg/L ALC solutions, respectively, for 2 days. The otoliths, fin rays, and scales of the fish were then sampled, visualized using fluorescence microscopy, and evaluated after 10 days. The ALC treatment was effective for marking certain hard structures and the marking color was affected by the light source. There were no obvious differences in the marking efficiency of rays from pectoral, dorsal, ventral, anal, and caudal fins, but the lapilli and lateral line scales were marked most effectively from the sampled otolith and scale types, respectively. Our findings indicate that ALC immersion and fin ray and scale sampling can be used for the effective marking and non-lethal evaluation of hard structures in juvenile silver carp.

AbstractIn this work, the genetic diversity of silver (Hypophthalmichthys molitrix Val.) and bighead (Hypophthalmichthys nobilis Rich.) carps bred on the territory of the Republic of Belarus was estimated according to genotyping of 11 STR loci (Hmo11, Hmo13, Hmo15, Hmo25, Hmo26, Hmo31, Hmo33, Hmo34, Hmo36, Hmo37, Hmo40). The following indices were calculated: average number of alleles per locus, effective number of alleles, levels of expected and observed heterozygosity, Shannon’s information index value, and FIS fixation index. The results obtained indicate a moderate (for bighead carp) and sufficiently high (for silver carp) genetic diversity of the studied samples, up to the possibility to allocate several groups for subsequent work on obtaining linear material and further reproduction. To achieve these goals, special attention should be paid to the selection of pairs of producers taking into account the results of molecular-genetic analysis. The estimation of genetic diversity of these species of herbivorous fishes bred in the Republic of Belarus as compared with the results of other studies indicates a significant genetic resource of domestic producers.

The paper describes in detail the structure of the connective tissue and of the bone components of the maxillary apparatus of the silver carp Hypophthalmichthys molitrix as well as the neighboring elements of the visceral skeleton and of the axial skull involved in the maxillary apparatus' functioning. The conclusions about the peculiarities of the maxillary apparatus in the process of pulsatile suction filtering are drawn based on the original anatomical study and on analysis of literature data.

The structure of some muscles, ligaments, the aponeurotic system, and osteological traits of the visceral apparatus in silver carp Hypophthalmichthys molitrix is considered in detail. A number of the revealed traits of the jaw apparatus indicate its adaptation to pulsed suction filtration. The functional features of the feeding apparatus are analyzed based on the anatomical study and data published in literature.