Great species to keep; robust, aggressive, and attractive. Definitely take the approach of buying multiple juveniles and growing them up, I would recommend between 5 and 6. Any fewer than 5 and I found the aggression was heightened and the dominant fish would set about hurting the others.
Reasonably difficult to sex from my experience (unless female is displaying the breeding colouration). Cannot rely on black dorsal mark reliably, I observed black dorsal in both sexes at various ages, however the female did exhibit a stronger black colour more regularly. In my fish I noted the male had a greater sized notch on its head while growing up, orange tint to the corners of its mouth, and showed more parallel black dots along flanks compared to female.
Not sure about how I feel about the 75g long term, certainly fine to grow them up in that. But an adult pair may need more space. I keep mine in a 450L.
They grow fast initially, I got growth rates of about an inch a month to the size of 4inch.
Provide space for less dominant fish to escape, I have a female convict in with mine (temporary) who retreats into a rock cave to avoid the larger Cubans.
They also share their tank with a small school of beunos aires tetras, although I think that the success of this pairing is dubious.
