Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
Matthew McConaughey was awarded a best actor Oscar for his performance in this film about the early days of HIV and AIDS treatment. We see him in a strip club where he sees a man who is a janitor at a hospital where he wants to get some experimental drugs to treat his AIDS disease. The janitor is reflected in a mirror next to an aquarium with an African Clawed Frog swimming in it. Later we see a close-up shot of the frog which looks like it is staring at McConaughey. I wouldn't be surprised if the tank was already at the bar location where the scene was filmed and they showed a close-up of the frog just because it was weird looking. I can't see any other reason or symbolism for why they showed it - unless somebody was aware of the part the frog once played in diagnosing pregnancies and its use in other lab studies, since this movie deals so much with studies of drugs for curing H.I.V. That seems like a far-fetched observation that only a crazy herp-obsessed person such as myself would try to make.