I'd never heard of "pothos" so I just looked it up. It's also called "Devil's Ivy." That doesn't sound too enticing! I tried to find out if it's poisonous (to fish anyway), and this site (and some others that I found) says it's poisonous (to humans I presume):
http://cas.bellarmine.edu/robinson/GoldenPothos.htmThat doesn't necessarily rule it out for use around the pond if the fish can't eat the leaves (can't reach them), etc. So, as long as the cuttings are out of the reach of the fish, it's probably safe to plant it around the pond.