Nothobranchius is a genus of small annual killifish found in Africa. Due to the relatively short lifespan, as well as easy breeding and care, Nothobranchius fish are becoming widely used as a vertebrate model system. Studying the genome and transcriptome of these fish is essential for advancing the field. In this study, we performed de novo transcriptome assembly of brain tissues from Nothobranchius guentheri using Trinity. Annotation of 104,271 potential genes (with transcripts longer than 500 bp) was carried out; for 24,967 genes (53,654 transcripts), in which at least one GO annotation was derived. We also analyzed the effect of a long-term food supplement with Torin 2, second-generation ATP-competitive inhibitor of mTOR, on the gene expression changes in brain tissue of adult N. guentheri. Overall, 1491 genes in females and 249 genes in males were differently expressed under Torin 2-supplemented diet. According to the Gene Set Enrichment Analysis (GSEA), the majority of identified genes were predominantly involved in the regulation of metabolic process, dendritic spine maintenance, circadian rhythms, retrotransposition, and immune response. Thus, we have provided the first transcriptome assembly and assessed the differential gene expression in response to exposure to Torin 2, which allow a better understanding of molecular changes in the brain tissues of adult fish in the mTOR pathway inhibition.