| Sex differentiation of tilapia is a synthetical mechanism controlled and coordinatedby heredity, physiology and environment. There are some influences of different levelson sex differentiation of tilapia about environmental factors, such as temperature, salinity,pH, exogenous hormones, photoperiod, population density, water quality, food abundanceand internal relationship between populations. The combined effects of four importantenvironmental factors （temperature, salinity, pH and17α-methyltestosterone） on sexdifferentiation of GIFT Nile tilapia （Oreochromis niloticus） were mainly examined in thestudy. It was aimed at finding out the changing trends of sex ratio of GIFT Nile tilapia,with the combined effects of these factors. The study should lay the foundation formasculine inducing of tilapia more effectively, and provide scientific basis for studing themechanism of sex differentiation of tilapia ulteriorly. The main conclusions in this studyrare as follows:1. The combined effects of temperature, salinity and pH on sex differentiation ofGIFT Nile tilapia （O.niloticus）The combined effects of three major environmental factors, temperature （T,2036C）,salinity （S,016） and pH （5.58.5）,on sex differentiation of GIFT Nile tilapia werestudied by using Box-Behnken design and response surface method. The results showedthat:（1） The linear and quadratic effects of temperature were highly significant （P<0.01）;the linear and quadratic effects of salinity and pH were nonsignificant （P>0.05）; theinteractions were nonsignificant between any two of the three factors （P>0.05）.（2） Withthe help of response surface method, the male rate of GIFT Nile tilapia increased withrising temperature. The maximum male rate,80%, was reached at the combination of36C/8/8.5.（3） The model equation of male rate on the three environmental factors wasestablished （R2=0.9748, pred.R2=0.9224）. By removing those nonsignificant factors, theoptimal model equation of the male rate on temperature was established （R2=0.9554,R2pred.=0.9347）, and could be practically used for forecasting the male rate. Temperaturemay be the most influential environmental factor on sex differentiation of tilapia. Thetemperature higher than34C could induce the masculinity of GIFT Nile tilapia notably, but not significantly affected by salinity and pH.The model equation had been established as follows:Y=1.3781-0.0707T-6.8073×10-3S-0.0287pH-5.8594×10-5T×S+1.8750×10-4T×pH+1.4792×10-3S×pH+1.5723×10-3T2-2.0898×10-4S2+1.3889×10-3pH2The optimized model equation had been established as follows:Y=1.2488-0.0694T+0.0016T22. The combined effects of temperature and feed17α-methyltestosterone concentra-tion （MT） on sex differentiation of GIFT Nile tilapia （O. niloticus）The combined effects of two major environmental factors, temperature （2036C） andfeed MT concentration （080mg/kg） on sex differentiation in Nile tilapia （GIFT strain）were studied using central composite face-centered design （CCF） and response surfacemethodology. The results showed that:（1） The linear effect of temperature on sexdifferentiation of the GIFT Nile tilapia was highly significant （P<0.01）, and the quadraticeffect was significant （P<0.05）. The linear and quadratic effects of the feed MTconcentration in feed were highly significant （P<0.01）; the interactive effect betweentemperature and MT concentration was significant （P<0.05）.（2） The male rate of the Niletilapia was gradually increasing varied with rising temperature, but varied with feed MTconcentration in a curvilinear way, using the response surface method. Moreover, theresults showed that the maximum male rate of GIFT Nile tilapia was94.4%, while the feedMT concentration was40mg/kg.（3） The model equation of the male rate towardstemperature and the feed MT concentration was established, with R2=0.9962and.R2Pred.=0.9749（P<0.01）, which could be practically used for forecasting the maleratio in the GIFT Nile tilapia.The model equation had been established as follow:Y=-8.3353+3.4309T+1.8516M+0.0071T×M-0.0473T2-0.0239M23. The combined effects of temperature, timing and duration of feeding with17α-me-thyltestosterone （MT） on sex differentiation of GIFT Nile tilapia （O.niloticus）Using Box-Behnken design （BBD） and response surface methodology, the effects ofthree major environmental factors, temperature （20C36C）, timing （day1to day31） andduration （10d30d） of feeding with MT, on sex differentiation of GIFT Nile tilapia werestudied. The results showed that:（1） The linear effects of temperature, timing and durationof feeding with MT on sex differentiation of GIFT Nile tilapia were highly significant（P<0.01）, and the interactive effects between any two of three environmental factors wasalso highly significant （P<0.01）. Furthermore, the quadratic effect of temperature washighly significant （P<0.01）, but the quadratic effects of timing and duration of feeding with MT were not significant （P>0.05）.（2） Using the response surface method, male rate ofGIFT Nile tilapia was gradually increasing with rising temperature, gradually decreasingwith delaying timing of feeding with MT, gradually increasing with overtiming duration offeeding with MT. Moreover, the results showed that the optimal combination wastemperature on36°C, timing of feeding with MT in the first day and duration of feedingwith MT was20d, at which the maximum male rate of the Nile tilapia （GIFT strain）arrived at94.4%.（3） The model equation of male rate towards temperature, timing andduration of feeding with MT was established，with R2=0.9944and R2Pred.=0.9378（P<0.01）.The model equation could be practically used for forecasting the male rate of GIFT Niletilapia.The model equation had been established as follows:Y=146.7083-9.7509T-1.2203t-3.4315D-0.0583T×t-0.0475T×D-0.0663t×D+0.2065T2-0.0060t2-0.0084D2... |
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