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Abstract Background Fish is favored by consumers, while amino acids and fatty acids are the main nutrients of muscle. At present, it has been found that the gut microbial community may be involved in the regulation of host material anabolism. Juvenile and adult bighead carp (A. nobilis) from Chagan lake and Xinlicheng reservoir were selected, and divided into four groups to compare the differences of gut microbial communities, free amino acid and fatty acids in muscle. Results The results showed that fish in different lakes or ages contained specific microbiota, the gut microbial structure was similar, but the microbial content was significantly different. Gut microbial abundance of juvenile fish in Chagan lake was significantly higher than that of other groups. Phylum level analysis Proteobacteria was the dominant gut bacteria of fish in both adult and juvenile fish from two separate lakes. Actinobacteria was another dominant bacterial phylum in juvenile fish in both lakes. Contents of free amino acids and fatty acids in muscle were detected, and the relationships between them and gut microbial communities were analyzed. Bighead carp grew from juvenile to adult, Actinobacteria abundance decreased (P

Background: Fish is favored by consumers, while amino acids and fatty acids are the main nutrients of muscle. At present, it has been found that the gut microbial community may be involved in the regulation of host material anabolism. Juvenile and adult bighead carp (A. nobilis) from Chagan lake and Xinlicheng reservoir were selected, and divided into four groups to compare the differences of gut microbial communities, free amino acid and fatty acids in muscle. Results: The results showed that fish in different lakes or ages contained specific microbiota, the gut microbial structure was similar, but the microbial content was significantly different. Gut microbial abundance of juvenile fish in Chagan lake was significantly higher than that of other groups. Phylum level analysis Proteobacteria was the dominant gut bacteria of fish in both adult and juvenile fish from two separate lakes. Actinobacteria was another dominant bacterial phylum in juvenile fish in both lakes. Contents of free amino acids and fatty acids in muscle were detected, and the relationships between them and gut microbial communities were analyzed. Bighead carp grew from juvenile to adult, Actinobacteria abundance decreased (P < 0.05) and Proteobacteria increased (P < 0.05). Proteobacteria was positively correlated with the contents of Thr, Lys, Pro, Asp, Gly and Glu, Actinobacteria was negatively correlated with Met and His. Meanwhile, EPA and DHA were positively correlated with Proteobacteria, EPA and DHA were not significantly associated with Actinobacteria. Conclusion: It was speculated that the contents of free amino acids and fatty acids in muscle might be affected by the difference of gut microbiota, thus affecting the taste and nutritional quality. [ABSTRACT FROM AUTHOR]

Purpose. Studying the peculiarities of the genetic structure of different age groups of silver and bighead carps from fish farm Limanske with the use of genetic-biochemical markers. Methodology. The methods of vertical polyacrylamide and horizontal starch electrophoresis with our own modifications have been used for the study. Sampling of the biological material and histochemical staining of gel plates were carried out using the generally accepted methods. Statistical analysis of the obtained data were performed in "Biosys-I". Findings. We analyzed the genetic structure of age-1, age-1+ and age-2 of silver and bighead carps with the use of genetic-biochemical markers - Рralb, EST, MDH, МЕ, СА. We demonstrated the peculiarities of allele frequencies and genotypic composition of protein system loci. A high level of heterozygosity in the examined was detected loci for age-1 silver carp – 66.7-88.9% and age-1 bighead carp – 65.4-77.8%. A significantly higher level of the observed average heterozygosity compared to the expected heterozygosity of age-1 as silver carp (Ho = 75.9%, He = 49,6%), and bighead carp (Ho = 73,6%, He = 47,9%) was observed. This fact indicated on the necessity for performing a stabilization of their genetic structure. The calculated Wright's F index in different age groups showed a predominance of the observed level of the average heterozygosity over the expected one for 22.7–53% in silver carp and 24.5-53.7% in bighead carp. A stabilization of the genetic structure in age-2 silver carp (Ho = 57.8%; He = 47.1%) by the heterogeneity level was observed. Originality. For the first time we analyzed the genetic structure and the level of heterogeneity of the breeding groups of age-1, age-1+, age-2 silver and bighead carps from fish farm Limanske with the use of genetic-biochemical markers. Practical value. The results of the study can be used in selection and breeding works aimed at creating the breeding stocks of silver and bighead carps to control the level of interspecies genetic variability. The obtained experimental data of the genetic structure analysis of silver and bighead carps of different age groups will be used for the monitoring of the genetic structure changes during their adaptation to new environmental conditions.

• Ultrasonication was applied to the thawing process of bighead carp. • Differences of thawing methods on quality of slow/fast frozen bighead carp were compared. • Shorten thawing time by ultrasound was observed. • Fast frozen samples lost massive water after water immersion or ultrasonic thawing. • Freezing-thawing cycles did not affect the primary protein structure of fish samples. Effects of ultrasound-assisted thawing (UAT), air thawing (AT) and water immersion thawing (WIT) on the quality of slow freezing (SF)/fast freezing (FF) bighead carp (Aristichthys nobilis) fillets were investigated. The thawing time of AT, WIT and UAT were 138, 30 and 12 min, respectively, indicating that UAT improved the thawing efficiency. UAT maintained the color and pH, and inhibited the lipid oxidation of SF/FF samples. For SF samples, thawing methods did not affect water retention and muscle structure. However, massive water loss and muscle destruction were observed in FF-WIT and FF-UAT samples. The AT did not produce any structural muscle damage; instead, it maintained the water retention in FF samples and prevented the FF fish fillets from massive water loss. No significant difference in the primary protein structure was observed among all samples. UAT can be an alternative strategy to the traditional thawing of SF fish fillets. [ABSTRACT FROM AUTHOR]