Judy,
It's definitely a pim, but I assume that that's not enough. From the pictures on www.scotcat.com I believe it to be a Leiarius pictus or a Sailfin Pim, but don't take my less-than-sage word on it!
~Matthew
P.S. Upon further review, I see the dorsal fin isn't quite the same, so I could also go with the Pimelodus albofasciatus, or White-Striped Pim.