When they mature
In the wild, redtails mature at about 78 cm standard length, measured without the tail, so roughly three feet or more in total. Spawning peaks in January and February, at the start of the flood.
Courtship in a tank
Captive adults do court. When the water warms from about 70°F to 80°F, mature adults swim together, touch barbels and nudge bellies. Tail-biting that follows is often mate testing.
But they will not spawn in a tank without help. A natural spawn needs a substrate to dig a pit nest, and farms instead use two hormones, then strip and mix eggs and milt by hand.
Where juveniles come from
Every redtail juvenile in the trade comes from farms or wild collection, not hobby breeders. They are now farmed routinely in Asia.