The aim of this study was to investigate the effects of dietary iron (Fe) levels on the growth performance, health status, meat quality, and intestinal flora of juvenile largemouth bass (Micropterus salmoides) and to determine the dietary Fe requirement of largemouth bass. Largemouth bass was fed with 6 isonitrogenous and isocaloric experimental diets containing Fe levels of 42.26, 50.79, 66.61, 80.86, 123.13, and 201.87 mg/kg for 10 weeks. The results showed that both final body weight (FBW) and specific growth rate (SGR) tended to increase and then decrease with increasing dietary Fe level, reaching their highest values of 50.34 g and 3.58%/d at a dietary Fe concentration of 80.86 mg/kg respectively. Feed efficiency (FE) and protein efficiency ratio (PER) increased linearly with increasing dietary Fe level. Total serum protein (TP) and urea nitrogen (UN) decreased linearly with increasing dietary Fe level. Serum superoxide dismutase (SOD) and catalase (CAT) enzyme activities tended to increase and then decrease with increasing dietary Fe level, while serum malondialdehyde (MDA) level tended to decline and then increase. In addition, increased dietary Fe level tended to improve muscle hardness and chewiness, thus improving meat quality. Analysis of the intestinal flora showed that the abundance of microorganisms such as Plesiomonas, Peptostreptococcaceae, and Lactococcus in the genus level increased significantly at dietary Fe concentrations of 80.86 mg/kg and 201.87 mg/kg, indicating that appropriate levels of dietary Fe can increase the diversity of intestinal microorganisms. Optimal dietary Fe levels for juvenile largemouth bass were determined to be between 73.81 and 83.22 mg/kg based on the broken-line regression analyses of SGR, FE, or hemoglobin content.

Microalgae are rich in fatty acids, proteins, and other nutrients, which have gained the general attention of researchers all over the world. For the development of Chlorella vulgaris in food and feed industry, this study was conducted to investigate the differences in C. vulgaris ’ growth and nutritional components under different culture conditions (autotrophic, heterotrophic, photoheterotrophic) and the internal factors through cell counting in combination with transcriptome and nutrient analyses. The results showed that, under the photoheterotrophic condition, Chlorella ’s growth and the contents of lipid and protein were significantly higher than that under the heterotrophic condition, and the moisture content was lower than that under the heterotrophic condition. The saturated fatty acid content under the photoheterotrophic condition was the lowest, while the polyunsaturated fatty acid content was significantly higher than those under the other two conditions. There were 46,583 differentially expressed genes (DEGs), including 33,039 up-regulated DEGs (70.93%) and 13,544 down-regulated DEGs (29.07%), under the photoheterotrophic condition in comparison with the autotrophic condition. The fold change between the two conditions of samples of up-regulated genes was higher than that of the down-regulated genes. The KEGG enrichment showed that the up-regulated DEGs in the photoheterotrophic condition were significantly enriched in 5 pathways, including protein processing in endoplasmic reticulum pathway, photosynthesis pathway, photosynthesis-antenna protein pathway, endocytosis pathway, and phosphonate and phosphinate metabolism pathway. DEGs related to fatty acid metabolic pathways were significantly enriched in the fatty acid biosynthesis pathway and the biosynthesis of unsaturated fatty acid pathway. The qPCR analysis showed that the expression pattern of the selected genes was consistent with that of transcriptome analysis. The results of this study lay a theoretical foundation for the large-scale production of Chlorella and its application in food, feed, and biodiesel. Key points • Nutrient levels under photoheterotrophic condition were higher than other conditions. • Six important pathways were discovered that affect changes in nutritional composition. • Explored genes encode important enzymes in the differential metabolic pathways.

The aim of this study was to investigate the energy sources and utilization patterns during embryonic development of Chinese sturgeon through analyzing the biochemical components of embryos at different development stages, and to explore the physiological characteristics and related molecular mechanism during embryogenesis in combination with an embryonic transcriptome analysis. Chinese sturgeon embryo samples were collected at different development stages (fertilized eggs, neurula stage, and tail touching head stage). The results showed that embryonic development was a process of continuous energy consumption. The change of total protein content was consistent with total amino acid content, showing a trend of increasing first and then decreasing. However, the total lipid content decreased significantly during early embryonic development. As for amino acid profile, leucine, arginine and lysine contents showed the highest level within essential amino acids (EAA), while glutamic acid, alanine, aspartic acid and serine contents showed the highest level within non-essential amino acids (NEAA). In terms of fatty acid content, the main quantitative fatty acids were C16:0 in saturated fatty acids (SFA), C18:1 in monounsaturated fatty acids (MUFA), and C22:6n-3 (DHA), C18:2n-6 as well as C20:5n-3 (EPA) in polyunsaturated fatty acids (PUFA). The content of C20:4n-6 (ARA), EPA and DHA were increased at neurula stage compared to fertilized eggs, which indicated their important roles in the structural composition during embryogenesis. Notably, Chinese sturgeon may have the ability to elongate n-3 PUFA to partially meet its requirements for highly unsaturated fatty acids (HUFA) during embryonic development. Transcriptome analysis showed that 19,078 and 6326 differential expressed genes (DEGs) were up-regulated and down-regulated respectively from fertilized eggs to neurula stage; while 3556 and 3150 DEGs were up-regulated and down-regulated respectively from neurula stage to tail touching head stage. KEGG enrichment analysis showed that the protein processing pathway was significantly enriched in early embryonic development through the up-regulated genes of imp4, pwp2, utp21, nop10, rpl10_17_35 and rps25; while the down-regulated genes of ccne1, ccna2, ccnb1, cdk1_2 and plk1 were associated with cell proliferation and differentiation pathway. In late embryonic development, the pathways related to aerobic metabolism, amino acid metabolism and lipid metabolism were significantly enriched through the up-regulated genes of mdh1, fumc, idh2, elovl6 and dgat2; and the neuroactive ligand-receptor interaction pathway was significantly down-regulated. In general, this study revealed the continuous energy consumption during embryonic development of Chinese sturgeon with specific energy substrates at different stages, and highlighted the DEGs and related pathway involved in the ontogeny and nutrient metabolism, which emphasizes the essentiality of high quality egg production for the success of captive breeding of Chinese sturgeon and would guide the broodstock nutrition for high quality egg production.

The primary cultured cells are maintained of r only short periods of time in vitro,and show similar biological characteristics with those cells in vivo,which are usually used as an excellent model system to investigate the normal physiological and biochemical properties of cells,as well as the effects of chemicals on cells and other aspects.The aim of the current study was to screen a suitable culture media for the grass carp muscle fiber growth under the primary culture condition.The muscle fibers of grass carp were isolated and cultured by tissue block method.Then the effects of different media on muscle fiber growth,cell morphology,migration time and first passage time were observed under an inverted microscope,the effects of different media on cell proliferation and adhesion rate were calculated by cytometry method,and the cell viability was measured by MTT method.In contrast to the DMEM and L-15,grass carp muscle fibers cultured in M199 medium showed a shorter time for tue migratios from the tissue block(P＜0.05),and a high cell adhesion rate,of(44.60±11.46)％than the cells cultured in DMEM and L-15 medium,which were(33.25±8.35)％and(22.83± 0.70)％,respectively(P＜0.05);Meanwhile,the M199 group showed a rapid cell proliferation rate,which only spent 72 h to achieve the log-growth phase,and the highest average amplification multiple of cells subcultured after 72 h(P＜0.05).Cell viability by MTT assay found that,the OD value of grass carp muscle fibers cultured in M199 medium was(1.03±0.17),which was higher than the OD values for DMEM and L-15(0.06±0.02 and 0.05±0.02),respectively(P＜0.05).To conclude,the growth and proliferation rates in M199 medium were significantly higher than those in DMEM and L-15 media,which indicated that M199 medium could pro-mote the growth of grass carp muscle fibers and could be used as a culture medium for the primary culture of grass carp muscle fibers.

The objective of this study was to evaluate the nutritional value of Clostridium autoethanogenum protein (CAP) as a sole protein source at different dietary protein levels by growth performance, health status, and intestinal microbiota of grass carp. Grass carp (4.56 ± 0.01 g) were randomly divided into 6 treatments in triplicate (30 fish per replicate) and fed with gradient protein level (24.45%, 27.31%, 31.82%, 35.79%, 38.64%, and 42.82%, respectively; named CAP1, CAP2, CAP3, CAP4, CAP5, and CAP6) diets for 8 weeks. Final body weight (FBW) and specific growth rate (SGR) were the significantly highest in the CAP4 group (P < 0.05). Based on SGR and feed efficiency (FE), the dietary protein requirement for juvenile grass carp was estimated to be 36.14–37.90%. CAP4 promoted hepatopancreatic health by reducing lipid deposition and structural lesions, and improved the anti-inflammatory ability by upregulating the relative expression level of il10 (P < 0.05). At the same time, the CAP4 improved the length of mucosal fold and the thickness of muscular layer. In addition, CAP4 can maintain the composition and metabolic function of intestinal microbiota and enhance the endocrine system and bacterial chemotaxis. However, it is worth noting that increasing CAP inclusion depressed hepatopancreatic antioxidant capacity. In conclusion, CAP is a promising novel protein source for grass carp, while careful consideration of its side effect at high inclusion level is deserved.

Skeletal muscle myoblastic cell lines can provide a valuable new in vitro model for the exploration of the mechanisms that control skeletal muscle development and its associated molecular regulation. In this study, the skeletal muscle tissues of grass carp were digested with trypsin and collagenase I to obtain the primary myoblast cell culture. Myoblast cells were obtained by differential adherence purification and further analyzed by cryopreservation and resuscitation, chromosome analysis, immunohistochemistry, and immunofluorescence. A continuous grass carp myoblast cell line (named CIM) was established from grass carp (Ctenopharyngodon idellus) muscle and has been subcultured > 100 passages in a year and more. The CIM cells revived at 79.78–95.06