In nature, in a cichlid spawn, the survival rate out of 1000 fry is usually no more than 1 (Ad Konings, Cichlids from Central America, 1989), which allows for only the fittest, the most robust, and instinctually savy to become a mature healthy adult and breed, allowing only those robust genes to be perpetuated..
In captivity, often many fry are saved, whether robust or not, allowing inferior genes to continue.
And when line bred for color varients are the goal , the profit motive assures, many that are not worthy pass on genes do.
Generally recognized in the unhealthy line bred forms such as "blue" Rams, and EBJDs among others.
And to suggest that tank size doesn't matter to inherently territorial fish such as "all" cichlids, is ignoring cichlid aquarium history, and science.
The other cichlids in the video are Mayaheros uropthalmus.
In the video below, is a Cenote dominated by uropthalmus, but the ones seen in the open, are subdominant males and females.
The 20" alfa males have caves in deep water, ultimate territories in the middle of the Cenote half the size of a football field each , and are assured they are only ones that get to spawn, and pass on robust genes.
As you can see the the subdominant males, and unresponsive females have been severely beaten by the dominant individuals, and relegated to te outer perimeter of the space.
Azul imovie edit