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.

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.

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.