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.

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.

Others that could be sexually dimorphic

Catoprion mento - Wimpel Piranha

Pristobrycon maculipinnis - Caribito

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

• Pygocentrus nattereri, Breeding by John Klonn

• Serrasalmus spilopleura  Breeding by H. Azuma

• Serrasalmus spilopleura Breeding Braker & E. Ledecky

• Piranha Eggs. Development

• Examining gonads - piranhas

REFERENCES:

• Magallanes, F. Sexual Dimorphism of the wimple piranha Catoprion mento (unpublished-1989). First appeared in OPEFE Journal of Piranhas and Predatory Fishes, Vol. 1, 1994, out of print. Copies may still  be obtained via the Aquatic Book Shop depending on availability.

• Cuvier, G. . 1819 Memoires du Museum National d'Histoire Naturelle, Sur les poissons du sous-genre «Hydrocyn, sur deux nouvelles espèces de «Chalceus», sur trois nouvelles espèces de «Serrasalmes», et sur l'«Argentina glossodonta» de Forskahl, quiest l'«Albula gonorhynchus» de Bloch. Mem. Mus. Natl. Hist. Nat.. 5:351-379.

• Ferreira, E.J.G., J.A.S. Zuanon and G.M. dos Santos, 1998. Peixes comerciais do médio Amazonas.. Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis. 211p.

• Géry, J.   1972 (19 Dec.) Poissons characoïdes des Guyanes. I. Généralités. II. Famille des Serrasalmidae. Zool. Verh. (Leiden) No. 122: 1-250, Pls. 1-16.

• Taphorn, D. C.   1992  The characiform fishes of the Apure River drainage, Venezuela. Biollania Edición Especial - No. 4. Monografias Cientificas del Museo de Ciencias Naturales, UNELLEZ -- Guanara, estado Portuguesa, Venezuela. 1-537.

• Bertin, L.   1948 Catalogue des types de poissons du Muséum national d'Histoire Naturelle. 3e partie. Ostariophysaires (Characiniformes, Gymnotiformes). Cat. Fish Types, Paris 3e partie: 1-49.

• Britski, H. A., K. Z. de S. de Silimon and B. S. Lopes   1999  Peixes do Pantanal. Manual de identificaçao. Embrapa. Serviçao de Produçal -SPI, Brasía, DF. Peixes Pantanal: 1-184.

• NAKAYAMA, C.M.; PORTO, J.I.R. & FELDBERG, E. (1998) Caracterização cromossômica de Catoprion mento (Characiformes, Serrasalmidae) do rio Uatumã, Manaus-AM. Resumos do VI Simpósio de Citogenética Evolutiva e Aplicada de Peixes Neotropicais: A2.

• BLEHER, Heiko, Search for the Wimple Piranha, (1993), Tropical Fish Hobbyist, pg.9-36.

• JANOVETZ,  Jeff, Functional morphology of feeding in the scale-eating specialist Catoprion mento. First published online December 2, 2005 Journal of Experimental Biology 208, 4757-4768 (2005) Published by The Company of Biologists 2005 doi: 10.1242/jeb.01938.

• Machado-Allison, A. & Fink, William., 1996, Los Peces Caribes to Venezuela Diagnosis, Claves, Aspectos Ecologicos Y Evolutivos.

• Machado-Allison, A.   2002 Los peces caribes de Venezuela: una aproximación a su estudio taxonómico. Bol. Acad. C. Fis. Mat. Nat. v. 62 (no. 1): 35-88.

• Reis, R. E., S. O. Kullander and C. J. Ferraris, Jr.   2003 Check list of the freshwater fishes of South and Central America. Check list Freshw. Fishes South & Cent. Amer. 2003: i-xi + 1-729.

• Magallanes, Frank, 1993, Feeding Seeds to Pygopristis denticulata.

• Cuvier, G., Memoires du Museum National d'Histoire Naturelle, Publishing date; 1819, Sur les poissons du sous-genre «Hydrocyn, sur deux nouvelles espèces de «Chalceus», sur trois nouvelles espèces de «Serrasalmes», et sur l'«Argentina glossodonta» de Forskahl, quiest l'«Albula gonorhynchus» de Bloch. Cuvier, G. . 1819 Mem. Mus. Natl. Hist. Nat.. 5:351-379.

• Müller, J. and F. H. Troschel   1844 Synopsis generum et specierum familiae Characinorum. (Prodromus descriptionis novorum generum et specierum). Arch. Naturgeschichte v. 10 (pt 1): 81-99 + Zu pag. 99 (foldout).

• Eigenmann, C. H.   1910 (12 Feb.) Catalogue of the fresh-water fishes of tropical and south temperate America. In: Reports of the Princeton University expeditions to Patagonia 1896-1899. Zoology. Catalogue v. 3 (pt 4): 375-511. [Also as a separate, issued 12 Feb. 1910 as: Catalog and bibliography of ...; Contr. Zool. Lab Indiana Univ. No. 76 (2).]

• Géry, J.   1972 (19 Dec.) Poissons characoïdes des Guyanes. I. Généralités. II. Famille des Serrasalmidae. Zool. Verh. (Leiden) No. 122: 1-250, Pls. 1-16.

• Géry, J.   1976 (18 Mar.) Les genres de Serrasalmidae (Pisces, Characoidei). Bull. Zool. Mus. Univ. Amst. v. 5 (no. 6): 47-54.

• Taphorn, D. C.   1992 The characiform fishes of the Apure River drainage, Venezuela. Biollania Edición Especial - No. 4. Monografias Cientificas del Museo de Ciencias Naturales, UNELLEZ -- Guanara, estado Portuguesa, Venezuela. 1-537.

• FINK, William L. and MACHADO-ALLISON, Antonio., Three new species of piranhas from Brazil and Venezuela. Ichthyological Explorations of Freshwaters, 3(1):55-71. 1992.

• MACHADO-ALLISON, Antonio and FINK, William., 1996 - Los Peces Caribes de Venezuela, Diagnosis, Claves, Aspectos Ecologicos Y Evolutivos, pg. 29-31.

• Photos of Pristobrycon maculippinis courtesy of www.mikofish.com .

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Updated: 07/09/2009