|Green, Bartholomew - Bart|
|RIZKALLA, ESAM - Egyptian Ministry Of Agriculture|
Submitted to: Global Aquaculture Advocate
Publication Type: Trade Journal
Publication Acceptance Date: 6/1/2016
Publication Date: 6/3/2016
Citation: Green, B.W., Rizkalla, E.H. 2016. Successful production of Nile and blue tilapia fry in a subtropical climate: based on degree days and demonstrated for earthen ponds. Global Aquaculture Advocate. Available: http://advocate.gaalliance.org/successful-production-of-nile-and-blue-tilapia-fry/
Technical Abstract: Degree-days can be used to adjust for seasonal variation in water temperature when planning tilapia fingerling production strategies and 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 whereas 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 is to feed newly hatched fry androgen-treated feed for three weeks. Newly 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. In this study, 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.