I would agree with most everything being said.....however I disagree with the above poster a bit, retic's really arn't that fragile you just can't treat them like crap. My female is over 3 years old and is on her second litter of pups, she is roughly 13 or so inches and eats everything in sight! Now both of my mature rays both retic's have very short tails...they both broke them during there transit from the wild and they don't regrow tails. But my one little pup already has a pretty long tail but she was born in the tank and really hasn't had to go through much moving. She came out a super good eater and she is a tough little booger and only around 2.5 inches at birth. I would go retic or true hystrix in a 90 but even then with the waste they produce you will be doing some mad water changes and should still upgrade when they get bigger. I had 3 retic's in a 125 for 2.5 years with a ton of other fish, but I was religious on my water changes 30% 2x a week with really good filtration. If you are seriousl about getting into rays with a 90 gal I would say only 1 and even though a retic is cheap they will cost you a ton in food well all rays will cost you a ton in food they are PIGS! Please read all of the stickies as they are a wealth of information that is where I started 3 years ago. Good luck and let us all know if you get one.
