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Sexual Dimorphism of Piranhas & Other Related Forms

By Frank Magallanes, February 17, 2006

 

Presently only one (1) species of piranha is scientifically recognized to be sexually dimorphic (Pygopristis denticulata). This dimorphism is based on a bilobed ( "D" a rounded projection that is part of a larger structure) anal fin of the male. This feature is unique among certain species and rare on the fish we call piranhas.  

 

One of the interesting things that I have read from other hobbyist is trying to determine whether their fish is a male or a female piranha. My usual response is that you won't know until they breed for you and you see the actual eggs spilling from the female piranha. There is really no hard and fast rule to determine sex on a piranha short of cutting them open. Some scientific articles at times relate to the female adult piranha being larger in terms of length. This correspondence well with the sexual maturity of piranhas of the species Serrasalmus maculatus and S. spilopleura. The adult female is usually longer and sometimes its girth may be a bit more evident than males. However, in your  home aquarium things are not the same as in nature.

 

How much you feed your fish and the size of your aquarium will give false impressions on the sexuality of your fish. So you must be careful not to assume anything on your captive piranhas in terms of sexual dimorphism. Coloration may also give a false positive on sex, as well as the size of the belly. Over eating or as is often the case, intestinal worms can over bloat a piranha giving it an appearance of it ready to release eggs.  Also, it is not uncommon to find unfertilized eggs in the aquarium. Females generally release this on a regular basis if they are not  absorbed by the body. Specimens dissected by me of piranhas appearing with fat bellies usually show putrid organs and full of blood. This type of atrophy is common with sick piranhas which often appear very dark in color. That is not to say every piranha that appears this way is sick! But it is something over enthusiastic hobbyist who think their piranha is ready to drop eggs, should be aware of.

 

FINS

FINS

 

In the examples above, separated by sex,  you can see the bilobed fins of the male piranha, including the Wimpel piranha (middle).  I have not been able to recognize this character with any other piranhas as of this date. However, that is not to say there are no other ones out there. Certainly, I would love to find more. But for now these 3 species shown here are the most current showing sexual dimorphism.

 

DENTICULA

Male P. denticulata

DENTICULATA

Female P. denticulata

ANAL FIN ANAL FIN

Others that could be sexually dimorphic

Catoprion mento - Wimpel Piranha

WIMPEL PIRANHA

Female C. mento

WIMPLE PIRANHA

Male C. mento

FINS FINS

 

Pristobrycon maculipinnis - Caribito

MACULIPINNIS

Male P. maculipinnis

MACULIPINNIS

Female P. maculipinnis

FINS FINS

 

It is my desire with publishing this discovery at OPEFE, that hobbyists will have an opportunity to try and breed the species. 

 

Other related topics

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