The Combined Effect of Several Environmental Factor on Fertilization, Hatching and Juvenile Growth of Nile Tilapia
|School||Guangdong Ocean University|
|Keywords||GIFT strain of Nile tilapia Environmental factors Central Composite Design (CCD) Box-Behnken Design (BBD) Response Surface Fertilization Hatching Larvae and juvenile|
(1) The effects of temperature, salinity and pH on the artificial fertilization rate （FR, %） and hatching rate （HR, %） of GIFT strain in O. niloticus by using of Box- Behnken Design and response surface method were studied. This study aimed to investigate the influence of simultaneous variation in temperature, salinity and pH on FR and HR of the GIFT strain of Nile tilapia （O. niloticus）, establish the equation of temperature, salinity and pH on the FR and HR and find out the optimal combination of temperature, salinity and pH through optimization techneque. The results showed that FR and HR declined with lower or higher temperature, salinity and pH. HR and FR were significantly affected by the linear and quadratic effects of temperature and salinity （P<0.001）. The synergistic effect between salinity and pH was nonsignificant （P>0.05） on FR, but significant on HR. The model equations were established of HR and FR: FR（%） = -721.373+34.462T+10.416S+76.478pH-0.568T2 -0.451S2-4.676pH2 - 0. 11T×S-0.284T×pH+0.133S×pH HR（%） =-774.789+36.955T+10.44S+83.898pH-0.646T2 -0.439S2-5.238pH2- 0. 051T×S-0.21T×pH-0.138S×pH These model equations were adequate with the determination coefficients respectively reached to 0.92 and 0.97 （P<0.01）, and they could be used to forecast tilapia’s HR and FR. By means of optimization technique, the optimal factor level combination for fertilization was derived, viz., temperature 27.30°C, salinity 20 and pH 7.40, at which the maximal fertilization was 87.68% with the desirability 92.11%. The optimal factor level combination for hatching was temperature 27.06°C, salinity 9.09 and pH 7.35, at which the maximal hatching percentage 81.18% with the dersirability as high as 96.74%. The optimal factor combination of fertilization was basically consistent with that of hatching, and it could be said that the greatest fertilization and hatching were simultaneously obtained at the optimal factor combination of 27.31°C/9.24‰/7.41. Thus the seed production efficiency of tilapia would be raised if this optimal combination is applicated in practice. （2） Previous studies revealed that the effects of density and flow rate on the hatching rate （HR, %） of GIFT strain of O. niloticus by using of central composite design and response surface method. Set the flow rate of 4-10 L.min-1; density range 0.5-2.5 (×104 ind.L-1). Study the effects of tilapia hatchery in density and flow rate, the establishment of density and flow rate and the relationship between hatching quantitative model, and through optimization techniques determine the optimal of density and flow rate combinations. The flow rate of hatching items and quadratic were highly significant （P<0.01）, the density of the quadratic term was significant for hatching rate （P<0.01）, the interaction of density and flow rate on the hatching were also affected significant （P<0.01）; but the density of the hatching was not effect （P>0.05）. The equation were established of HR:HR （%）= -6.9552-1.2427F-0.6080D+0.0882F2 +0.5391D2-0.1164F×D The coefficient of determination was 0.9463 （P<0.01）, the equation can be used to predict hatching. Using statistical optimization techniques, the optimum density range 1.0-2.0 (×104 ind.L-1), flow rate was 6.5-9.5 L.min-1; the hatching rate was 84.81% in the density of 1.43 (×104ind.L-1), flow rate of 7.98 L.min-1. The hatching rate of tilapia can effectively improve in the suitable density and flow rate.（3） Using central composite design and response surface methods of ammonia nitrogen (A, mg.L-1) and nitrite (N, mg.L-1) GIFT strain of Nile tilapia hatching （HR, %） and larval activity （SAI） effects. The study changes ammonia and nitrite, while effect the Nile tilapia hatch and larvae activity, established the quantitative model of ammonia, nitrite and hatching and larval activity. With the increasing of ammonia and nitrite concentration, the hatching and larvae activity also decreased of the tilapia. The ammonia and nitrite on hatching and larval activity had highly significant effects （P<0.01）. The synergy of ammonia and nitrite affect significant （P<0.05）. The secondary of ammonia or nitrite had no significant effect on tilapia hatching （P>0.01）; but the secondary of ammonia on the activity of larvae was significantly （P<0.05）. Establishment the polynomial dynamic of hatching and larval activity of tilapia:HR （%）= 88.5805-1.1055A-1.0318N-0.0264A×N-0.0042A2 +0.0255N2 SAI = 18.9933 - 0.2229A - 0.3899N - 0.0095A×N - 0.0084A 2 + 0.0075N2 The coefficient of determination were 0.9740 and 0.9729, the results can be used as an important basis for breeding of water regulation and help to improve seed rearing.（4） Previous studies revealed that the effects of ammonia nitrogen (A, mg.L-1) and nitrite (N, mg.L-1) on the growth of larvae of GIFT strain of O. niloticus by using of central composite design and response surface method. This study aimed to obverse the influence of simultaneous variation in ammonia nitrogen and nitrite ongrowth of larvae, build the equation of ammonia nitrogen and nitrite on the absolute growth rate (AGR, g.d-1), characterized growth rate (SGR, %.d-1) and weight gain rate （GBW, %）. With the increasing of ammonia and nitrite concentration, the growth also decreased of the tilapia. The effect of ammonia, secondary effects and the synergies of ammonia and nitrite on the growth had a significant effect （P<0.05）. The nitrite on the growth had a significant effect （P<0.05）, but the secondary of nitrite had no significant effect on growth （P>0.05）. The polynomial of tilapia growth was established as follows:AGR （g- d- 1 ）=0.0226-0.0009A-0.0007N+3.7041×10-5A×N+1.6565×10-5A2 - 7.2121×10 -6 N2 SGR (%- d-1 )=13.5286-0.1737A-0.1436N+0.0042A×N+0.0019A2+0.0005N2GBW（%） = 4224.8602-174.7553A-133.5192N+6.9132A×N+3.0918A2 -1.3480N2 The coefficient of determination of the AGR, SGR, GBW were respectively 0.9861, 0.9745 and 0.9860. The results will provide scientific basis for water quality management of tilapia culture; can also serve as an important basis for breeding of water regulation and help to improve seed rearing.