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The present study aimed to compare the nutritional effects of cholesterol, bile acids, and combination of cholesterol with bile acids in plant-based diets on juvenile genetically improved farmed tilapia (GIFT; Oreochromis niloticus). The isonitrogenous (321 g/kg crude protein) and isolipidic (76 g/kg crude fat) diets (Con diet) were based on plant protein sources, which included corn gluten meal, soybean meal, cottonseed meal and rapeseed meal. The Con diet was supplemented with 12 g/kg cholesterol (CHO diet), 0.2 g/kg bile acids (BAs diet), a combination of 12 g/kg cholesterol and 0.2 g/kg bile acids (CHO–BAs diet), respectively. Each diet was fed to three tanks in an indoor recirculating aquaculture system for 9 weeks. Results showed that compared to the Con group, fish had a higher weight gain rate, hepatosomatic index, and a lower feed conversion ratio in the CHO–BAs group. The highest levels of whole-fish fat and ash were found in the Con group. Serum parameters, including activities of alanine aminotransferase (ALT) and aspartate transaminase (AST), along with levels of glucose (GLU) and triglyceride (TG) except for total cholesterol (TCHO), were lower in the CHO, BAs, and CHO–BAs groups than those in the Con group (P < 0.001). Histological examination revealed that fish in the Con group exhibited severe hepatocyte vacuolization and diminished hepatocyte proliferation. Gene expression analysis indicated that the transcriptional levels of bile acid metabolism-related genes (including fxr, fgf19, bsep) were up-regulated in the CHO–BAs group (P < 0.05), whereas cholesterol metabolism-related genes (acly and hmgcr) were down-regulated in both CHO and CHO–BAs groups (P < 0.001). Moreover, UPLC-MS/MS analysis revealed that the higher taurine-conjugated bile acids (T-BAs), followed by free bile acids (Free-BAs) and glycine (G-BAs) were determined in tilapia bile. Among these, taurochenodeoxycholic bile acid was the predominant bile acid. Dietary bile acids supplementation also increased the proportion of T-BAs (tauro β-muricholic acid and taurodehydrocholic acid) while decreasing Free-BAs in the fish bile. In conclusion, the incorporation of cholesterol with bile acids into plant-based diets can effectively reduce cholesterol uptake, suppress bile acids synthesis, enhance bile acids efflux, and promote hepatocyte proliferation, which is helpful for maintaining the normal liver morphology in tilapia, and thus improving its growth performance.

Nile tilapia (Oreochromis niloticus) is a worldwide farmed fish and has been widely used for the study on comparative immunology in teleosts. It is well known that cadmium (Cd) can cause a variety of adverse effects in fish. However, data on the effects of Cd in fish liver and the defensive mechanisms of these effects using transcriptome approach are relatively scarce to date. In this study, by using an RNA sequencing approach, the gene expression profiling was performed in livers of tilapia exposed to 0 (control), 50, 100, and 200 μg/L of Cd for 2 months. The results showed that exposure to 50 μg/L Cd altered the expressions of 911 genes, while exposure to 100 and 200 μg/L Cd resulted in 4318 and 3737 differentially expressed genes compared to the control. Weighted correlation network analysis (WGCNA) and gene ontology (GO) analysis identified a 14-gene network linked to the immune system development. Further, in a fuzzy analysis, the GO term immune system development was enriched in cluster 3, and gene expression decreased with increasing Cd levels in a concentration-dependent manner. The qPCR and RNA-seq results identified 4 genes, i.e., dnmt3bb.1, sf3b1, SMARCAL1, and zap70, as convenient potential biological indicators for detecting waterborne Cd. The present results help systematically understand the effects of Cd on the hepatic transcriptome in tilapia.

BackgroundInterspecies hybridization is an important breeding method to generate fishes with heterosis in aquaculture. Using this method, hybrid Nile tilapia (Oreochromis niloticus, ♀) × blue tilapia (Oreochromis aureus, ♂) has been produced and widely farmed due to its growth and appetite superiorities. However, the genetic mechanism of these advanced traits is still not well understood. Ghrelin is a crucial gene that regulates growth and appetite in fishes. In the present study, we focused on the expression characteristics and its regulation of ghrelin in the hybrid.ResultsThe tissue distribution analysis showed that ghrelin was predominantly expressed in the stomach in the hybrid. Ghrelin was more highly expressed in the stomach in the hybrid and Nile tilapia, compared to blue tilapia, showing a nonadditive pattern. Two single-nucleotide polymorphism (SNP) sites were identified including T/C and C/G from the second exon in the ghrelin gene from Nile tilapia and blue tilapia. By pyrosequencing based on the SNP sites, the allele-specific expression (ASE) of ghrelin in the hybrid was assayed. The result indicated that ghrelin in the hybrid showed higher maternal allelic transcript ratios. Fasting significantly increased ghrelin overall expression at 4, 8, 12, 24, and 48 h. In addition, higher maternal allelic transcript ratios were not changed in the fasting hybrids at 48 h. The cis and trans effects were determined by evaluating the overall expression and ASE values in the hybrid. The expression of ghrelin was mediated by compensating cis and trans effects in hybrid.ConclusionIn summary, the present lines of evidence showed the nonadditive expression of ghrelin in the hybrid tilapia and its regulation by subgenomes, offering new insight into gene expression characteristics in hybrids.

The escalating problem of copper (Cu) and cadmium (Cd) pollution in aquatic environments poses a significant threat to the ovarian tissue and reproductive capacity of fish, hindering the development of the aquaculture industry. However, the combined effects of Cu and Cd on fish gonadal development remain unclear. In this study, the fish species Nile tilapia was stressed with rearing water containing 300 μg/L Cu2+ and 100 μg/L Cd2+ for 30 days, followed by an intraperitoneal injection of luteinizing hormone-releasing hormone (LHRH-α) and human chorionic gonadotropin (HCG) at various concentrations. We investigated the ovarian transcriptome profiles before and after injection. Prior to injection, combined treatment with Cu and Cd resulted in reproductive dysfunction and metal ion imbalance in tilapia. Transcriptomic profiling revealed differential gene annotation concentrated in the MAPK signaling pathway and regulation of GTPase activity. Post-injection, all concentrations of LHRH-α and HCG groups showed an upregulated gonadosomatic index (G.S.I) and higher levels of vitellogenin (VTG), gonadotropin-releasing hormone (GnRH), gonadotropin (GTH), and estrogen (E2) in serum compared to the negative control group. Transcriptomic analysis revealed alterations in various ovarian signaling pathways, preliminarily revealing the in vivo molecular mechanisms and differences in LHRH-α and HCG. The findings from this study could help us better understand how to counteract the effects of combined Cu and Cd exposure on tilapia ovarian development, which has significant implications for the Nile tilapia aquaculture industry.

【Objective】The study was conducted to explore the effects of compound probiotics on the growth performance and muscle quality of tilapia and aquaculture water environment under zero-water exchange condition, with a view to providing references for emission reduction as well as efficient and healthy aquaculture in fishery industry.【Method】Taking tilapia as research object and regular water exchange aquaculture mode as control group, a full-cycle aquaculture test of tilapia was carried out by adding compound probiotics under zero-water exchange condition (experimental group), and a comparative analysis on growth performance, muscle quality of tilapia and main water quality, microbial community structure was conducted.【Result】Under zero-water exchange condition, the survival rate of tilapia of the experimental group was 83.3%, significantly higher than the control group; feed coefficient was 2.3, significantly lower than the control group; as for the muscle quality, crude protein content of the experiment group was 22.17%, significantly higher than the control group. Main water quality of the experimental group stayed stable through the full-cycle of aquaculture period, the water temperature was 26.5-30.5℃, pH was 7.0-8.0, nitrite of water sample was 0.039 mg/L, significantly lower than the control group. The dominant bacteria was similar between experimental and control groups, however, the diversity index of the experimental group was higher than that of the control group.【Conclusion】Under zero-water exchange condition, adding compound probiotics in aquaculture water improved the survival rate of tilapia, reduced the feed conversion rate, and improved the muscle quality of tilapia. Meanwhile, the experimental group had strong improving effects on the water environment of aquaculture to some certain extent, and increased the diversity index of bacterial community. During the whole aquaculture production cycle, the zero-water exchange aquaculture of tilapia with high-activity compound probiotics had a good substitution effect for the conventional aquaculture model which relies on frequent water changes to release environmental pressure.

Circular RNA (circRNA) is an endogenous biomolecule in eukaryotes. It has tissue- and cell-specific expression patterns and can act as a microRNA sponge or competitive endogenous RNA. Although circRNA has been found in several species in recent years, the expression profiles in fish gonad are still not fully understood. We detected the expression of circRNA in the ovary, testis, and sex-changed gonad of tilapia by high-throughput deep sequencing, and circRNA-specific computing tools. A total of 20,607 circRNAs were obtained, of which 141 were differentially expressed in the testis and ovary. Among these circRNAs, 135 circRNAs were upregulated and 6 circRNAs were downregulated in female fish. In addition, GO annotation and KEGG pathway analysis of the host genes of circRNAs indicated that these host genes were mainly involved in adherens junction, androgen production, and reproductive development, such as ZP3, PLC, delta 4a, ARHGEF10, and HSD17b3. It is worth noting that we found that circRNAs in tilapia gonads have abundant miRNA-binding sites. Among them, 935 circRNAs have a regulatory effect on miR-212, 856 circRNAs have a regulatory effect on miR-200b-3p, and 529 circRNAs have a regulatory effect on miR-200b-5p. Thus, our findings provide a new evidence for circRNA–miRNA networks in the gonads in tilapia.