|Green, Bartholomew - Bart|
|Teichert-coddington, David - Auburn University|
|Rizkalla, Esam H - Egyptian Ministry Of Agriculture|
Submitted to: World Aquaculture Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/5/2016
Publication Date: 6/26/2017
Citation: Green, B.W., Teichert-Coddington, D.R., Rizkalla, E. 2017. Degree-days as a tool for use in producing tilapia fry for sex inversion [abstract]. World Aquaculture Society Meeting, June 26-30, 2017, Cape Town, South Africa. p. 234.
Technical Abstract: Hormonal sex inversion of newly hatched tilapia fry continues to be an important method to produce monosex male tilapia fingerlings. Large numbers of tilapia fry suitable for sex inversion can be produced by periodic complete harvest of earthen reproduction ponds. Traditionally, harvest interval was based on the assumed tilapia reproductive cycle. Water temperature affects tilapia reproduction and growth, and in the tropics and subtropics varies seasonally and with elevation. Degree-days, also known as the rule of thermal summation, is a calculation used to quantify temperature effects on biological processes, and has been used by entomologists, agronomists, and, to a lesser extent, fisheries biologists. The relationship between degree-days and production in earthen ponds of fry suitable for sex inversion was quantified in the tropics for Nile (Oreochromis niloticus) tilapia and in the subtropics for Nile and blue (O. aureus) tilapia. Earthen reproduction ponds (0.01-0.05 ha) in Honduras (tropics) and Egypt (subtopics) were stocked with tilapia broodfish at 0.6-1.0 fish/m2 (1.5-2.2 females per male). Ponds were drained 13-21 days after stocking, the broodfish removed en masse and transferred to a holding tank, and fry harvested from the harvest sump using dipnets (1.6-mm ace nylon mesh). Harvested fry were graded through 3.2-mm square mesh plastic netting and numbers determined; fry passing through the netting were suitable for sex inversion whereas retained fry were too large. A total of 33 and 26 independent trials were conducted in Honduras and Egypt, respectively. No tilapia fry were observed at fewer than 140 degree-days in Honduras, although females incubating eggs were observed at 120-140 degree-days, whereas in Egypt no fry were observed at fewer than 125 degree-days. Total fry production in both countries increased linearly as degree-days increased from 125-276, but the proportion of fry too large for sex inversion increased linearly as degree-days increased beyond 200. Total length of fry suitable for sex inversion averaged 9.4 and 8.9 mm for Nile and blue tilapia, respectively, and 14.4 mm for fry too large for sex inversion. Range in number of days until reproduction pond harvest in relation to mean weekly pond water column temperature for optimal production of Nile tilapia and blue tilapia fry (7–13 mm total length) suitable for hormonal sex inversion. Optimal production of fry suitable for sex inversion occurs between 190 degree days (lower curve) and 220 degree days (upper curve).