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TThe length-weight relationships (LWRs) were determined for five freshwater fish species collected from Liangzi Lake, the Xi River and Longxi River in China, including Megalobrama amblycephala, Megalobrama skolkovii, Megalobrama pellegrini and Megalobrama terminalis belonging to the genus Megalobrama, as well as white Amur bream (Parabramis pekinensis) of the genus Parabramis. Three of these five species had no previous LWR estimates in the FishBase. The LWRs of hybrids from Megalobrama amblycephala ♀ × Parabramis pekinensis ♂ and Megalobrama amblycephala ♀ × Megalobrama terminalis ♂ were also reported for the first time.

Intermuscular bone (IB) is a type of membrane bone that derive from the continuous homogeneous ossification of the connective tissue in fish muscle. Collagen genes involved in the regulation of vertebrate bone mineralization, but it is not clear whether its expression is related to the development of fish intermuscular bones. In order to study the correlation among collagen genes and IB formation, this study first analyzed the phylogenetic evolution of type I and IIcollagen genes in fish; then compared genes expression levels at different stages and tissues between Megalobrama amblycephala with intermuscular bones and Oreochromis niloticus without intermuscular bones. Phylogenetic analysis of the collagen genes col1a1, col1a2 and col2a1 showed that fish species with IB and species without IB were clustered into different branches, and the amino acid homology of M. amblycephala and O. niloticus genes was less than 90%. There were significant differences between the expression levels of col1a1a and col1a1b genes in M. amblycephala and homologous genes col1a1 in O. niloticus in several muscle (dorsal, upper caudal and lower caudal muscles). In M. amblycephala, the expression levels of type I and type II collagen genes in the dorsal muscle were higher than those in the caudal muscle; however, in O. niloticus, the expression of these genes was opposite to that of M. amblycephala. The expression of col1a1a and col2a1b genes of M. amblycephala increased significantly before the appearance of intermuscular bones (15 dph) and after the appearance of all intermuscular bones (50 dph). The relative expression of type I collagen gene and col2a1b were significantly different in different periods, and the expression abundance of col1a1a at 50 dph was extremely high. Compared with M. amblycephala, the expression change of these genes in Oreochromis niloticus were small, and the overall fluctuation was not large. These results revealed that the expression level and pattern of col1a1 in two species were significantly different (P<0.01), therefore we speculate that col1a1 is potentially related to the development of IB. [ABSTRACT FROM AUTHOR]

As one of the most sustainable protein sources for humans, aquaculture is the fastest growing food production sector in agriculture. According to the recent FAO estimate, there are 21 principal aquaculture fish species around the worldwide. Among these cultured species, almost half of them belong to Cypriniformes, the species from which all have a certain number of intermuscular bones (IBs). IBs are small spicule‐like bones existing in the muscle fillet, which are existed only in lower teleost and of course have a negative effect on fish quality and aquatic product processing. Many studies have been focusing on IBs number, morphology, and more and more become focusing on its development molecular mechanism. In the review, we summarized the recent progress and discussed with following directions: (i) Controversial on the origin of IBs, ossified from tendons or ligaments? (ii) IBs counts and morphology revealed big variation among different species; (iii) Ossification patterns of IBs might be related with different swimming modes among the teleost fish, and its development belongs to intramembranous ossification without cartilaginous phase; (iv) Transcriptome/microRNA (miRNA)/proteomics and gene functional analysis had been used to investigate the molecular mechanism of IBs development and some genes showed certain regulatory roles during IBs' development; (v) The reports showed that some breeding technologies could make a certain effect on IBs counts in fish species, but there are rare reports with success on deleting or significantly reducing IBs counts. Meanwhile, we also discuss the challenges and future directions of reducing or even deleting IBs in aquaculture. [ABSTRACT FROM AUTHOR]

Background/Aims: Fish is a protein-rich food and is increasingly favored by consumers. It has been well recognized that the flesh composition of fish is closely related to its maturation and growth stage, but few studies have explored these differences. Additionally, hormone residues in fish after artificial induction of reproduction also attract consumer concern. In this study, we attempt to address these concerns by using a combination of transcriptomics and metabolomics analyses to identify key regulated pathways, genes, and metabolites that may affect the flesh nutrition of one typical aquaculture species in China, blunt snout bream (Megalobrama amblycephala). Methods: The four groups of fish were used for transcriptomics and metabolomics analyses, including one-year-old immature (group I), two-year-old immature (group II), two-year-old mature (group III) and successfully spawned (group IV) female M. amblycephala after artificial induction of reproduction. Results: We identified a total of 1460 differential compounds and 1107 differentially expressed unigenes in muscle among the different groups. Differential metabolites related to fish age (group II vs group I, group III vs group I) were largely enriched in “Glycerophospholipid metabolism”, “Linoleic acid metabolism”, “α-Linolenic acid metabolism”, and “Biosynthesis of unsaturated fatty acids”. Between these two pairwise comparisons, metabolites that are beneficial to human health, such as docosapentaenoic acid, α-Linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid were found to be significantly decreased in two-year-old (group II, group III) compared with one-year-old (group I) M. amblycephala. Only one differential metabolite related to fish maturation, a triglyceride, was detected between groups III and II. Transcriptomics data showed that differently expressed genes (between group III vs group II, group III vs group I) related to maturation were highly enriched in “Cell adhesion molecules (CAMs)”, “Sphingolipid metabolism” and “Phagosome”. DEGs (between group II vs group I, group III vs group I) relating to fish age were enriched in the “cGMP-PKG signaling pathway”, “FoxO signaling pathway”, and “AMPK signaling pathway”. The gene-metabolite interaction network showed pivotal genes, including fumarate hydratase and GNPAT, which played a major role in the regulation of glycerphospholipid metabolism. The nutritional components were also measured, which verified the metabolomics results. Moreover, the metabolomics results showed that after 24 hours of artificial hormone injection, the drug was completely metabolized. Conclusion: Integrated analysis demonstrated that the nutrition value of fish fillet was much more related to fish age compared with maturation status in M. amblycephala females. [ABSTRACT FROM AUTHOR]