The Combined Effect Of Several Important Environmental Factors On The Growth And Development Of Tilapia

1)The combined effects of temperature and salinity on the yolk absorptionefficiency of Nile tilapia sac fry were investigated using central compositeexperimental design and response surface approach. According to the preliminarytrials, temperature was determined to range from22°C to34°C, and salinity range isset to2ppt-10ppt. The absorption efficiency was mensurated in terms of yolk sacvolume. Results showed that the linear effects of temperature and salinity on the yolkabsorption efficiency was highly significant (P<0.01); the quadratic effects of and theinteraction between the two factors were significant (P<0.05); temperature was moreimportant than salinity in influencing the yolk absorption efficiency. The modelequation of yolk sac volume towards temperature and salinity was established. Fromthose high R2values, the model had excellent goodness of fit to experimental data andcould be applied for predictive purpose. What with the production cost, it is suggestedthat the temperature/salinity combination, i.e.,28-30°C/4-6ppt, be employed duringthe period of sac fry rearing, in which the yolk absorption efficiency was on average98.6%.2)We studied the quantitative relationship of the first feeding rate (FFR,%) totemperature and salinity in GIFT strain of Oreochromis niloticus by use the centralcomposite design and response surface method and determined the optimalcombination of temperature and salinity for the fry from newly hatched to the firstfeeding utilizing model optimization. Through preliminary experiments temperaturewas determined to range between20°C and34°C, salinity range is set to2ppt-10ppt.Results showed that the liner effect of temperature on the first feeding rate (FFR) washighly significant (P<0.01), and that of salinity on FFR was significant (P<0.05); theinteraction effect of temperature and salinity on the FFR was not significant (P>0.05);quadratic effect of temperature on the FFR was highly significant (P<0.01), and thatof salinity on FFR was significant (P<0.05); temperature was more important thansalinity in impacting on the FFR. The model equation of FFR towards temperature and salinity was established, with R2=0.9861, adjusted R2=0.9721and predictiveR2=0.9112. This showed that the goodness-of-fit of model was extremely high andcould be used to predict the FFR of newly hatched tilapia larvae. Through optimizingthe model equation built, results showed that when the combination of temperatureand salinity lay at29°C/5ppt, the FFR reached the maximum of87.97%, with thereliability as high as0.972. In practical production of tilapia larvae, especially theearly stage from newly hatched tilapia larvae to the first feeding, the productionefficiency of tilapia larvae would be sharpened if the optimal combination oftemperature and salinity is applied.3)We studied effects of light intensity and photoperiod on tilapia hatchability(HR,%), larval survival factor (SAI) experiments using CCD design and RSM. Bythe preliminary experiments, light intensity range was set to100lux-1400lux,photoperiod was set to2h-24h. Results showed that the linear effects of photoperiodon hatching was not significant(P>0.05), and that of photoperiod on larval survivalwas significant(P<0.05); the linear effects of light intensity on hatching was highlysignificant(P<0.05), and light intensity on larval survival was not significant(P>0.05);the interaction effect of photoperiod and light intensity on the hatching and larvalsurvival were not significant (P>0.05); quadratic effect of photoperiod and lightintensity on the hatching and the larval survival were highly significant (P<0.01), Themodel equation of hatching and larval survival towards photoperiod and lightintensity were established. the coefficient of determination reached more than97percent, and that of forecast reached more than86%,and it could be used to forecastTilapia’s HR and SAI. Through optimizing the model equation built, results showedthat when the combination of photoperiod and light intensity lay at15h/699lux, theHR and SAI reached the maximum of90.14%and41.77, The results of this study hassome significance to further improve the quality of tilapia seed cultivation.4)Using central composite design(CCD) and response surface methodology(RSM),we studied the effects of different photoperiod and intensity on the specific growth rate(SGR) and feed conversion rate(FCE) of tilapia larvae.By the preliminary experiments,photoperiod was set to range from6h-24h, intensity was100lux-2000lux. Results show,the linear effects of photoperiod on SGR and FCEwere not significant(P>0.05);the linear effects of light intensity on SGR was highly significant(P<0.01), and that oflight intensity on FCE was significant(P<0.05); the interaction effectof photoperiod and light intensity on the SGR and FC E were not significant (P>0.05); quadratic effect of photoperiod on SGR was significant(P<0.05),and that of photoperiod on FCE was highly significant(P<0.01);quadratic effect of light intensity on SGR and FCE were highly significant(P<0.01). The model equation of SGR and FCE towards photoperiod and light intensity were established. Coefficient ofdetermination reached98.75%, respectively,99.13%.The model had excellent goodness of fit to experimental data and themodel was appropriate. Through optimizing the model equation built, results showed that when the combination of photoperiod and light intensity lay at14hL:10hD,1267lux, the SGR and FCE reached themaximumof7.47%/d and138.55%. The findings provide a reliabletheoretical basis and technicalsupport for tilapia fingerlings enterprises.