That's why I plan to keep at least 10 Paretroplus of a single species.
but it's not that weird; we should be used to cichlids that kill each other when the group's too small....Petrochromis, Tropheus, Simochromis, Pseudosimochromis, Eretmodus, Melanochromis, Pseudotropheus, Metriaclima etc etc
all of these turn on each other when you keep 5 or so, some of them even need to be kept with at least 12 or the whole group will implode
it still doesn't keep people from breeding them. Tropheus for example are very popular, so are many Mbuna's.
"And he piled upon the whale's white hump the sum of all the rage and hate felt by his whole race. If his chest had been a cannon, he would have shot his heart upon it"