I assume you mean the hybrid of the RTCxTSN. I think they are lovely, and it must be great to watch a fish with the predatory habits of the TSN with the mouth of the RTC.
No-one is really sure how big they will get. TSNs get past 3 foot easily, and Captive RTC have hit 5 feet.
I believe they are a hormonally injected cross-breed developed in the hope of attaining a fast growing food fish for that area of South America - I have read that the local natives tend not to eat RTC due to the colour of its meat.