Clownfish are not transgender. First of all, gender is a social construct that we can't prove animals even posess the mental capacity for. Secondly, clownfish actually, physically change sex. Thirdly, sex works very differently in fish in general and clownfish in particular - their sex is not determined by chromosomes but instead entirely depends on hormones which can change depending on various circumstances (in case of clownfish it has to do with the group of clownfish, for other species it can depend on water temperature, age, salinity,...) and is not as fixed as it is in mammals (and even in mammals it's not as fixed as most of us were taught in school). What I'm trying to say is clownfish aren't trans, they're hermaphrodites - in my opinion, you can't really say they change to the "opposite sex" if their sex was pretty loosely defined to begin with.