Red zebra cichlids are mouth-brooding mbuna cichlids. Females incubate the eggs and carry their young around in their mouths. In order to breed these fish and witness this behavior, ensure you have a male and a female.
You can differentiate between full-size males and females by their size. Males grow larger than their female counterparts. Males grow to more than 5 inches long, while females max out at 4 inches. However, this method assumes that the fish are both fully grown. A fish 5 inches long is likely a male, but those 4 inches or shorter may be juveniles, females or undersize males. These measurements are in "standard length," the practice of measuring a fish from the front of the face to the base of the tail.
Many mouth-brooding cichlids have marking called egg spots. These are brightly colored spots on the anal fin. The anal fin is single fin on the bottom of the fish at the end of the fish's abdomen. Both male and female red zebras have these markings. Males' are larger and more numerous. This difference exists among all the different color variations of this fish.
Another means of telling male fish from females is by behavior. Males will act more aggressive than females. Male red zebra cichlids are very combative and will chase away other fish, particularly other males. Additionally, only males clean spawning sites. So if you have a fish that meticulously fawns over a rock, it is probably a male. In this species, only the female carries the young, so if you see a fish with a mouthful of eggs, it must be a female.
Coloration can help differentiate between males and females, but caveats exist. The biggest problem is that red zebra cichlids come in different color morphs. A color morph is a naturally occurring color pattern different from the standard coloration for a species. Color morphs are not different species or subspecies, but they look so different they may be mistaken for other fish. In the "standard" red zebra, males are bright red-orange and females are blue. However, in some color morphs of the red zebra, both males and females are red or blue. You should probably rely on the other methods to differentiate between males and females.
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