Transcriptome Analysis Reveals Differential Gene Regulation in Ovarian Tissues of Anabas testudineus (Bloch, 1792) in Response to Insecticide, Monocrotophos

Monocrotophos (MCP), an organophosphate insecticide commonly used in agriculture, has raised concerns due to its runoff into aquatic ecosystems and causes potential adverse effects on fish. The present study envisaged the understanding of the impact of MCP on the ovarian tissues of Anabas testudineus (climbing perch), an air-breathing food fish often found close to agricultural fields, making it a valuable bio-indicator of agrochemical contamination. Transcriptome profiling of ovarian tissues in response to 45 days of MCP exposure at sub-lethal concentrations was performed. Using Illumina platform sequencing, a total of 144.51 million reads were produced. After filtering and trimming, 138.82 million high-quality reads were obtained, of which 96.10% were mapped to the Anabas genome. Expression analysis revealed a total of 54 significant differentially expressed genes (DEGs), including 28 upregulated genes, and 26 downregulated genes compared to the control group (Log2 FC >  ± 1 and, adjusted p-value < 0.05). Gene ontology analysis of the DEGs revealed associations with molecular, biological, and cellular functions. Key detoxification genes, such as glutathione S-transferase and UDP-glucuronosyltransferase, were significantly upregulated, indicating an enhanced detoxification response to MCP. In contrast, cytochrome P450 family 1 subfamily A (cyp1a1), a gene critical for steroid hormone metabolism, was downregulated, suggesting disruptions in hormone regulation. Functional enrichment analysis highlighted several affected processes, including steroid hormone biosynthesis, oocyte meiosis, apoptosis, and progesterone-mediated oocyte maturation. The randomly selected eight DEGs using RT-qPCR confirmed consistent gene expression levels in line with the transcriptome data. This work identified significant genes associated with detoxification and reproduction events in the ovarian tissues for maintaining homeostasis. This will also serve as valuable information for further investigation of the association of the identified genes with the reproductive biology of fish in response to toxicants or pollutants.