Flagtail prochilodus fish Id?

[catfishacr]

Hey is it possible to tell by these pics if i have a Semaprochilodus insignis or Semaprochilodus taeniurus? It was sold to the fish store as a flagtail prochilodus. Thanks for the help!!

 

[FJB]

Old thread.
However, S. taeniurus (young) for sure. S. insignis has more numerous (~10) visible black bars on tail, recognizable even when in juveniles the tail has not reddened yet.

 

[AncientFishArk]

Curious, I've never had one of these but have seen them around. I was at the doctor and saw a smaller one, about 5inch.

How big to these guys get?
How aggressive?

Mouth looks to be like a algae eater.

Comments?