That's acidity, particularly when you experience it close to sides among the tongue. As we've suggested, a little knowledge goes longer way, and, for many of us us, it's all we need to be able to fully enjoy our wine experience. Another way is to try poaching the fish within a saucepan of wine. https://reilly-duffy-4.blogbright.net/wine-tasting-techniques-for-your-beginner