This is true, although there are lots of freshwater "sharks" as they are called. So far, I would rate the Labeo rubropunctatus as the most aggressive "shark" I have kept. followed by my black shark, then red gilled violet shark, then labeo parvus, then labeo calbasu, then labeo barbatus. Red tail black sharks are pussy cats in comaprison and even further down the pecking order is the rainbow/red finned sharks. Other one like apollo sharks, cigar sharks are not aggressive at all in my experiance.
This thread is more derail than info. All caused by the OP. Thanks to those that tried to provide real info. But, I'm closing this since it has a better chance of getting worse than getting better.