A new approach for the detection of trimethylamine (TMA) using a recombinant cell line of Xenopus laevis melanophores was developed. The cells were genetically modified to express the mouse trace amine-associated receptor 5 (mTAAR5), a G protein-coupled receptor from the mouse olfactory epithelium, which conferred high sensitivity to TMA. Cellular responses to TMA were analyzed by two different techniques, either by absorbance measurements using a microplate reader or by cellular imaging via an inverted microscope. A focused chemical screen allowed the discovery of additional, previously unknown stimuli of mTAAR5. The developed cell-based sensor demonstrated no sensitivity to trimethylamine N-oxide (TMAO), making it suitable for a straightforward evaluation of TMA levels in fish tissue extracts. For the detection of TMA vapor, the cells were covered with agarose, which allowed for intact cell viability for at least 6h in air. The developed gas measurement platform was able to detect TMA from 1 to 100 ppm within 35 min.