A lfs recently had some black darter tetra in stock but unfortunately I had to pass since I didn't have a planted tank ready to go and didn't want to risk losing the batch. Plus I've read about how notorious they are to feed and keep going. 3yrs is a very long time considering they were probably wild caught and who knows how old they were when collected.
As far as the fish pictured above they are very active tetras. They are very quaralsome amongst themselves as they compete for territory in the tank or for a females attention but rarely do any damage to eachother. I have some as small as 1-1.5cm that are already trying to join the adults (4-4.5cm) in the main group. They are egg scatterers the male will chase a female against the plants until she drops her eggs. Of course there is a dominant male with the best colors who usually stays in his prime spot while the others stay together on the other side of the tank. The tank is a heavily planted 90gal tank with only some otos and blue pearl shrimp for algae cleanup.