IMO, it is a Pimelodus blochii or a close look-alike. It is not a maculatus, who has even rows of well-defined, large spots -- http://www.planetcatfish.com/common/species.php?species_id=312 -- (not sure if the shot #2 is correct as it is an adult/large fish but the rest appear correct, even though some fish are too stressed/pale)