well first off, jds get really aggressive. my jd who was about 6'' at the time killed 3 of my 10'' oscars. i had a smaller 1 in another thank (im guessing 3'' at the time) and i was forced to put them together because both fish would kill everything. goodthing i did because now they are mating. they require the same care as an ocar would, but if you add any fish, witch i wouldnt recommend, make sure they are much bigger and keep an eye on him.
they are very much like oscars but more aggressive. they can be less social, but mine swim around begging for food like my os
i bet that fish is much happier with you
the males are much more colorfull and have a very pointed dorsal fin. sometimes it can be hard to tell if the fish was fed wrong, stressed, or has damage on its fins. this could leed to a lack of color and a rounded top fin, which may make a male look like a female.
they have always been one of my favorite fish, but they just get too damn aggessive. id never even attempt to mix species in with jds. they are hardy fish, beautiful in color, and easy to breed and take care of.