Its dead or dying, if it went in your tank yesterday then IMO there were issues before you bought it. Or your water quality is extremly bad. As asked already how did you acclimate it? It looks very bleached, mouth gaping open and expelling anything with those other conditions is not good. I would take it out if it has a very bad ordor get rid of it its completly gone. IMO even if it doesnt your chances of bringing it back to a healthy state are slim and none.