Deutscher Tropentag, October 9 - 11, 2002 in Kassel-Witzenhausen
"Challenges to Organic Farming and Sustainable Land Use
in the Tropics and Subtropics"
Effects of Rearing Temperatures on Sex Ratios in Tilapia, Oreochromis niloticus L., Investigations on a Local Population from the Lake Victoria in Kenya
Albert Altena, Gabriele Hörstgen-Schwark
Georg-August University Göttingen, Institute of Animal Husbandry and Genetics, Germany
High rearing temperatures are suspected to shift the sex ratio towards males in different strains and populations of the Nile Tilapia, Oreochromis niloticus. To test, whether a local population of O. niloticus is sensible to high rearing temperatures, research trials were conducted on progenies, derived from brooders originating from the Winiam Gulf, the Kenyan part of the Lake Victoria. All investigations were carried out at a testing unit, including newly constructed closed recirculation systems for the rearing of brooders and artificial incubation of eggs, at Maseno University, Kenya during a research stay from October 2000 till May 2001.
Eleven batches could be tested, which encompassed a 10-day temperature treatment, fry on-growing until an age of 90 days post fertilisation and final sex determination by inspection of the gonads. From these 11 batches all temperature treated progenies showed a high tendency towards males in their sex ratios. The overall male ratio in the treatment group was 79.1% while for the control the male ratio was 54.1%. This reflects a difference of 25%. In 6 of these batches the difference regarding the sex ratio between treatment group and their respective controls was significant (t-test).
The results indicate that, the tested population of O. niloticus from the Lake Victoria shows response to a temperature treatment in order to shift the sex ratio of temperature treated progenies towards males. The results further indicate that due to no homogenous reactions regarding the response of high rearing temperatures on sex determination, the lability of sex ratio to elevated temperatures might be dependant on specific breeding pairs and therefore it might be a heritable trait.
Keywords: Kenya, Oreochromis niloticus L., sex determination, temperature sensibility
Contact Address: Albert Altena, Georg-August University Göttingen, Institute of Animal Husbandry and Genetics, Albrecht-Thaer-Weg 3, 37075 Göttingen, Germany, e-mail: albert_altenahotmail.com