Scientists develop technique to sex Arapaima

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A major step has been taken in the domestication of the pirarucu (Arapaima gigas) with the development of a technique to accurately sex the fishes non-invasively.

The details of the method, developed by Fred Chu-Koo and coauthors, are to be published in an upcoming issue of the journal Fish Physiology and Biochemistry.

The method involves assaying the blood of the fish for levels of plasma vitellogenin, 17-estradiol (E2) and 11-ketotestosterone (11KT), with the authors verifying the sex of the subjects by sacrificing them and examining the gonads.

From previous studies with other fish species, the level of plasma vitellogenin is higher in female fish than in males, and the 11KT:E2 ratio is higher in male fish than in females.

Based on the method developed by the authors, they were able to sex the fish with 95% accuracy using plasma vitellogenin and with a 100% accuracy using the 11KT:E2 ratio.

The non-invasive method of sex determination has important implications for the long-term success of culturing the pirarucu.

Prior to this study, no reliable method of determining the gender of the pirarucu existed, save for some changes in colour when the fishes have initiated courtship.

Current methods of culturing this species are inefficient, relying on natural reproduction of brooders of an unknown sex ratio are introduced to an earthen pond.

The authors write, "s fry production is one of the most important activities in any aquaculture initiative...it is very important firstly to distinguish the sex of broodstock individuals for fish larval production.

"This fact is particularly true for large fish showing no morphological difference between male and female. Rearing excess A. gigas broodstock in ponds or cages wastes space and food and results in economic losses."

For more information, see the paper: Chu-Koo, F., R Dugu, MA Aguilar, AC Daza, FA Bocanegra, CC Veintemilla, F Duponchelle, J-F Renno, S Tello and J Nuez (2009) Gender determination in the Paiche or Pirarucu (Arapaima gigas) using plasma vitellogenin, 17-estradiol, and 11-ketotestosterone levels. Fish Physiology and Biochemistry doi: 10.1007/s10695-008-9211-8