Jinglin Zhu

As a green aquaculture model, aquaponic systems have considerable potential for improving the aquaculture environment, but their effects on produced animals remain insufficiently understood. In this study, a Houttuynia cordata-based decoupled aquaponic system was established for Nile tilapia production. Its effects on the aquaculture water environment and physiological status of Nile tilapia were evaluated through water quality monitoring, serum biochemical analysis, hepatic antioxidant assessment, and brain stress-related gene expression. The system reduced ammonia nitrogen, nitrite nitrogen, total phosphorus, permanganate index, and suspended solids, while reductions in total nitrogen and sulfide occurred only at specific time points. The system also improved hepatic function, lipid metabolism, and renal function. Notably, hepatic CAT, SOD, and GSH-Px activities increased, indicating enhanced enzymatic antioxidant defense. In brain tissue, gad2 and penk were upregulated, whereas comtb and pnmt were downregulated, suggesting altered neural regulation and stress-related responses. Overall, the Houttuynia cordata-based decoupled aquaponic system improved the aquaculture water environment and multiple aspects of Nile tilapia physiology, particularly hepatic enzymatic antioxidant defense, while modulating neural- and stress-related responses.

(1) Background: Nile tilapia is a cornerstone of global aquaculture, yet hypoxia remains a critical constraint. This study investigates the hypoxia response mechanisms in the gill tissue of a selectively bred Egyptian strain to elucidate the metabolic pathways and genetic regulators governing its tolerance. (2) Methods: We evaluated antioxidant and metabolic enzyme activities alongside gill histology after hypoxia exposure. Furthermore, transcriptome profiling was conducted to identify enriched pathways, with expression patterns validated via qPCR to distinguish between acute and long-term adaptive responses. (3) Results: Hypoxia significantly altered enzyme activities and caused time-dependent gill damage, ranging from mild swelling to severe rupture. Transcriptomics highlighted starch/sucrose metabolism and PPAR signaling. qPCR confirmed that specific genes peak at 6 h for acute responses, while others gradually increase for long-term adaptation. (4) Conclusions: These findings link energy metabolism with immune regulation, revealing the molecular mechanisms underlying hypoxia tolerance. The identified genes offer valuable insights and genetic resources for breeding resilient Nile tilapia.

Salinity stress represents a critical environmental constraint that significantly limits the development of tilapia aquaculture in brackish water environments. Its substantial impacts on fundamental physiological processes in fish, particularly osmotic balance, energy metabolism, and antioxidant defense mechanisms, have become a major scientific concern in aquaculture research. To systematically elucidate the molecular mechanisms underlying the response of genetically improved farmed tilapia (Oreochromis niloticus) to salinity stress and to test the hypothesis that it adapts through metabolic reprogramming for energy reallocation under such conditions, this study employed an integrated transcriptomic and metabolomic approach. Through a rigorously controlled experimental design with freshwater (0‰) as the control group and brackish water (24‰) as the experimental group, we conducted a comprehensive analysis of dynamic changes in gene expression profiles and metabolite spectra in the liver tissues of experimental fish. The study yielded the following key findings: First, salinity stress significantly suppressed growth performance indicators, including body weight and length, while simultaneously inducing extensive transcriptomic restructuring and profound metabolic remodeling in liver tissue. A total of 1529 differentially expressed genes (including 399 up-regulated and 1130 down-regulated genes) and 127 significantly differential metabolites were identified. Second, the organism achieved strategic reallocation of energy resources through coordinated suppression of multiple energy-consuming anabolic pathways, particularly steroid biosynthesis and fatty acid metabolism, with the remarkable down-regulation of Fasn, a key gene in the fatty acid synthesis pathway, being especially prominent. Energy-sensing and metabolic homeostasis regulatory networks played a central coordinating role in this process, guiding the organism through metabolic reprogramming by regulating downstream metabolic nodes. From a multi-omics integrative perspective, this study provides in-depth insights into the sophisticated metabolic remodeling and energy allocation strategies employed by GIFT to cope with salinity stress. These findings, particularly the suppression of fatty acid biosynthesis and the reprogramming of glycolysis/gluconeogenesis pathways, not only elucidate the molecular mechanisms by which teleosts achieve environmental adaptation through energy reallocation, but also provide actionable molecular targets for the selective breeding of salinity-resilient tilapia strains.

Hybridization is a widely used breeding technique in fish species that enhances desirable traits in cultured species through heterosis. However, the mechanism by which hybrids alter gene expression to form heterosis remains unclear. In this study, a group of hybrid tilapia was used to elucidate heterosis through interspecies crossing. Specifically, p38 was analyzed to describe the regulation of gene expression variation in hybrid tilapia. Transcripts from the Nile tilapia allele were found to be significantly higher than those from the blue tilapia allele in hybrid individuals, indicating that the expression of p38 was dominated by Nile tilapia sub-genomic alleles. The study also found a compensatory interaction of cis- and trans-acting elements of the Nile tilapia and blue tilapia sub-genomes, inducing a non-additive expression of p38 in hybrids. Eight specific SNPs were identified in the p38 promoter regions of Nile tilapia and blue tilapia, and were found to be promoter differences leading to differences in gene expression efficiencies between parental alleles using a dual-luciferase reporter system. This study provides insights into the non-additive expression patterns of key functional genes in fish hybrids related to growth and immunity response.

Luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) belong to the gonadotropic hormone receptors (GtHR), which are highly expressed in fish gonads and participate in the regulation of fish reproductive activities. Fish gonadal development and gamete maturation are not only regulated by their BPG axis but also affected by natural environmental factors (such as temperature, salinity, pH, nutrients, light, etc.). Nile tilapia (Oreochromis niloticus) is a farmed fish with a short reproductive cycle, fast growth, and high economic value. To study the relationship between gonadotropic hormone receptors (GtHR) and the reproductive activity of Nile tilapia, different oxytocin injection experiments and different temperature treatment experiments were set up, and the expression changes of the GtHR gene in the gonads and the concentration changes of the estradiol (E₂) in the female serum and testosterone (T) in the male serum were determined employing a quantitative RT-PCR assay and enzyme-linked immunosorbent assay (ELISA), respectively. After the injection of oxytocin, with the change of E2 in females and T in males, the FSHR showed an expression pattern of first increase, then decrease, and the LHR showed an expression pattern of first increase, then decrease, and finally increase in the gonads, and the expression level of FSHR and LHR in the injection group was significantly higher than that in the control group at multiple time points; in addition, the expression level of FSHR and LHR in the oxytocin-combination injection group was higher than that in the single injection group. During 28 days of treatment at different temperatures, the sex steroid hormones and GtHR genes also showed regular changes, and the relationship between each group was 28 °C > 32 °C > 24 °C at most time points. According to the research results, it is speculated that FSHR and LHR play an important role in the development of Nile tilapia gonads and participate in the reproductive activities of Nile tilapia. By comparing and analyzing the changes in the sex steroid hormones and GtHR genes in each experimental group, it is speculated that different oxytocin injections could affect the expression of FSHR and LHR genes in Nile tilapia, and the combined effect of oxytocin was better than single oxytocin; the optimum temperature for the reproduction of Nile tilapia is between 28–32 °C. This study provides a theoretical basis for further elucidating the physiological functions and molecular mechanisms of FSHR and LHR and also provides a reference for the research of reproductive regulation in Nile tilapia.

Heterosis is a widespread biological phenomenon in fishes, in which hybrids have superior traits to parents. However, the underlying molecular basis for heterosis remains uncertain. Heterosis in growth and survival rates is apparent in hybrid tilapia (Oreochromis niloticus ♀ × O. aureus ♂). Comparisons of growth and hematological biochemical characteristics and mRNA and miRNA transcriptional analyses were performed in hybrid and parents tilapia stocks to investigate the underlying molecular basis for heterosis. Growth characteristics and hematological glucose and cholesterol parameters were significantly improved in hybrids. Of 3097 differentially expressed genes (DEGs) and 120 differentially expressed miRNAs (DEMs) identified among three stocks (O. niloticus, O. aureus, and hybrids), 1598 DEGs and 62 DEMs were non-additively expressed in hybrids. Both expression level dominance and overdominance patterns occurred for DEGs and DEMs, indicating that dominance and overdominance models are widespread in the transcriptional and post-transcriptional regulation of genes involved in growth, metabolism, immunity, and antioxidant capacity in hybrid tilapia. Moreover, potential negative regulation networks between DEMs and predicted target DEGs revealed that most DEGs from miRNA-mRNA pairs are up-regulated. Dominance and overdominance models in levels of transcriptome and miRNAome facilitate the integration of advantageous parental alleles into hybrids, contributing to heterosis of growth and improved survival. The present study provides new insights into molecular heterosis in hybrid tilapia, advancing our understanding of the complex mechanisms involved in this phenomenon in aquatic animals.

Hybrid tilapia were produced from hybridization of Nile tilapia (Oreochromis niloticus) and blue tilapia (O. aureus). Comparative transcriptome analysis was carried out on the liver of hybrid tilapia and their parents by RNA sequencing. A total of 2319 differentially expressed genes (DEGs) were identified. Trend co-expression analysis showed that non-additive gene expression accounted for 67.1% of all DEGs. Gene Ontology and KEGG enrichment analyses classified the respective DEGs. Gene functional enrichment analysis indicated that most up-regulated genes, such as FASN, ACSL1, ACSL3, ACSL6, ACACA, ELOVL6, G6PD, ENO1, GATM, and ME3, were involved in metabolism, including fatty acid biosynthesis, unsaturated fatty acid biosynthesis, glycolysis, pentose phosphate pathway, amino acid metabolism, pyruvate metabolism, and the tricarboxylic acid cycle. The expression levels of a gene related to ribosomal biosynthesis in eukaryotes, GSH-Px, and those associated with heat shock proteins (HSPs), such as HSPA5 and HSP70, were significantly down-regulated compared with the parent tilapia lineages. The results revealed that the metabolic pathway in hybrid tilapia was up-regulated, with significantly improved fatty acid metabolism and carbon metabolism, whereas ribosome biosynthesis in eukaryotes and basal defense response were significantly down-regulated. These findings provide new insights into our understanding of growth heterosis in hybrid tilapia.