Examining Piranha Gonads: Is it possible for a hobbyist to determine sex using scientific methods?
by Frank Magallanes - February 18, 2005
There is much interest among hobbyists that breed piranhas if it is possible to determine sex of a piranha during fry stages by examining the belly region via bright light and magnification. This question was brought forth after I made available information found on the internet about Medaka Fish and the examination of ovaries.
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Photo courtesy of National Academy of Sciences |
Unfortunately, it is not possible for just anyone
to do it. The gonadal examination of Pygocentrus piraya is an often cited
article by hobbyists who believe they can sex piranhas using this method.
However, it is a complex procedure and the fishes used in that report were in
the range of 6 cm to 34 cm SL (juvenile to adult). The gonads were examined by
histological sections by embedding them in paraffin blocks and slicing, and
couter staining with eosin/hematociciline. This is the standard method at
looking at egg development. Using the Medaka model above it is also not possible
to see ovaries on piranha fry fish as well. Gonads are under-developed in fry
fish, therefore not possible to determine sex of piranhas. Some hobbyists have
reported seeing granules or globule like objects similar to the Medaka model.
Those are more than likely fat beads. Larvae and/or fry that consume brine
shrimp naupalii will also give the illusion of eggs in that region, but
it is undigested food (see photo upper left).
Presently, the only piranha species known to be sexually dimorphic (external sexual characteristics) is Pygopristis denticulata, the anal fin is bi-lobed.
REFERENCES
BLACKSMITH, R.M.A.; BAZZOLI, N.; RIZZO, E.; SATO, Y. - reproductive Aspects of piranha, Pygocentrus piraya (Teleostei, Characiformes), native species of the basin of the River Sâo Francisco. Arq. Bras. Med. Vet. Zootec. 48 (supl. 1): 71-76, 1996.
CROSS, A.M.G.; SATO, Y.; RIZZO, E.; SAINTS, G.B.; BAZZOLI, N. sexual Maturação of piranha Pygocentrus piraya (Cuvier, 1820) (Pisces, Characidae) in the dam of Three Marias, Minas Gerais. Bios , 4 (4): 17-22, 1996.
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.
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