How to Identify a Male Lionfish From a Female

By Jo Jackson

Lionfish have a spectacular appearance with distinctive fins and striped patterns that make them an ideal candidate for home aquariums. They also are known as scorpionfish, dragonfish, tigerfish and butterfly cod. There are about 22 species of lionfish in two genera, all are tropical fish with venomous spines. It is important to know the sex of your lionfish as it is not recommended to have more than one male in a tank.

Different Species

Lionfish species reach different sizes ranging from 2 to 18 inches. Different species have different markings, different length fins and a different number of fin spines. They all tend to be solitary animals who come together to mate and form small groups with one male and two to seven females. Males are highly territorial and some species are more aggressive than others, with males more likely to kill each other rather than chase the other away.

Mating Behavior

The easiest time to tell male lionfish from female ones is when they are ready to mate. The males turn darker and the stripes are less visible, while the female turns paler. Mating usually occurs just after sunset and the belly, mouth and throat of the female turn silvery white so she is easier to see. The male circles the female and they ascend to the top of the water where she trembles her fins and releases her spawn, which he fertilizes.

Head Size

Male lionfish tend to have larger heads than females. If you are looking at two or more lionfish of the same species, the one with the larger and more square-shaped head will be the male. Physical characteristics do vary between the species so it is important to research the lionfish species that you want to breed. Fuzzy dwarf lionfish are one of the easiest species to determine the sex by the head size.

Fins and Stripes

In most species of lionfish the males have longer pectoral fins that extend beyond the middle of the caudal peduncle. The female pectoral fins only reach the base of the caudal peduncle. Within each species males also tend to have more stripes on the pectoral fins. For example in fuzzy dwarf lionfish the males have 6 to 10 stripes while the females have four to six stripes. Research your chosen species to find out their specific characteristics.