Assets are dozens of times bigger in build than on disc

Hello, I have a 2D game here which i want to release on android and IOS. im trying to debug why my build size got much higher for no apparent reason. Through the Asset Bundle Browser i believe to have a rather accurate description of what textures and animations i have included in my scenes. I do not load anything from resources etc., everything is included from the start. All assets summed up take up about 25Mb. The final build size is 173Mb. I am 100% sure that there was a time when the final build size was not that much larger than my asset size. Through the Editor Log after the building process i tried to debug where the sizes comes from. The Build Report states that Textures make up 99.4%(772.6mb umcompressed) of my size usage. After that there is a list of assets sorted by filz size. The first one is a random sprite taking up 10.4mb. However on disc that sprite is 39.3Kb big... I cant figure out why everything is so much bigger in the build...