|Green, Bartholomew - Bart|
|RIZKALLA, ESAM - Egyptian Ministry Of Agriculture|
Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2015
Publication Date: 6/9/2015
Citation: Green, B.W., Rizkalla, E.H. 2015. Nile tilapia and blue tilapia fry production in a subtropical climate. Journal of Applied Aquaculture. 27:132–143.
Interpretive Summary: Pond water temperature varies seasonally in tropical and sub-tropical regions of the world where tilapia is cultured. This seasonal variation in water temperature generally does not result in tilapia mortality, but can delay tilapia reproduction. Degree-days can be used to adjust for seasonal variation in water temperature when planning tilapia fingerling production strategies. Degree-days are calculated by subtracting a threshold temperature ("biological zero") from the mean daily water temperature; the threshold temperature is the temperature below which development is halted by cold and is not necessarily 32 degrees Fahrenheit. When water temperatures are cooler greater time can be allowed for optimal tilapia reproduction and less time is required at warmer temperatures. Populations of all-male tilapia fingerlings are preferred for stocking into grow-out ponds because male fish grow faster than female fish. One method of producing populations that contain greater than 98-99% male fish is by sex inversion, which is achieved by incorporating an androgen into the feed fed for three weeks to newly hatched tilapia fry. Recently hatched tilapia fry 9 to 11 mm total length are preferred for sex inversion because they are presumed to be sexually undifferentiated. The relationship between the production in earthen ponds of fry suitable for sex inversion and degree-days was quantified for Nile and blue tilapia in Egypt. No tilapia fry of either species were produced at fewer than 125 degree-days and above that total fry production increased as cumulative degree-days increased to 280. However, the optimal production of Nile and blue tilapia fry suitable for sex inversion was obtained when ponds were harvested after 190 to 215 degree-days. The use of degree days was shown to be a good predictor for pond production in Egypt of Nile and blue tilapia fry for sex inversion and this work confirmed results obtained for Nile tilapia in Central America.
Technical Abstract: The relationship between production in earthen ponds located in a subtropical climate of fry suitable for hormonal sex inversion and degree-days was quantified for Nile tilapia (Oreochromis niloticus; Egypt strain) and blue tilapia (O. aureus). Degree-days were calculated for each trial as the sum of mean daily water column temperature minus the reference temperature, 15 degree C. No fry from either species were harvested at fewer than 124 – 126 degree-days. Total fry production for each increased linearly as cumulative degree-days increased from 129 – 281 degree-days. Production of fry suitable for hormonal sex inversion was positively related to cumulative degree-days only from 115 – 215 degree-days. Tilapia fry too large for hormonal sex inversion were not observed until greater than 200 cumulative degree-days, and increased with increasing degree-days thereafter. Optimal production in earthen ponds in a subtropical climate of Nile tilapia and blue tilapia fry suitable for hormonal sex inversion was obtained at 190 – 215 degree-days.