With cichlids from the genus Parachromis (like managuense) outward difference can be very obvious, but with cichlids like oscars, outward differences are almost invisible .
Take this Parachromis motaguense (close cousin to the jaguar).
Male
female
With most Parachromis, males have small spots on the lower gill plate, females only a few larger ones, or none.
No such luck with Oscars