There are actually a couple of diseases that can be contracted from fish. I don't remember what they were, but one of them was pretty nasty. There is also, in a reef tank, the danger of palytoxin getting into a cut from zoanthids and palythoa. Coral nemacysts are VERY effective if they touch a cut place. The right one will leave you hopping around saying things you wouldn't want your mother to hear you say. Latex gloves will prevent all of this. The shoulder length gloves probably should be used if you have any open cuts.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.