The Effect Of Carbohydrates Addition On Water Quality And Feed Efficiency In Tilapia Ponds

Water scarcity, disease prevalence, increasing feed expenses and concerns onbio-security lead to minimizing water exchange and use of feed for tilapia culture insouth of China. Biofloc technology （BFT） is a new approach toward water treatmentand waste protein recycling. The basic principle of the BFT is the retention of waste andits conversion to biofloc as a natural food based on the activity of the microbialcommunity within the pond. By inputting carbohydrates to the pond, the microbes takeup the ammonium from the waste water and create microbial protein which is supposedto be used by tilapia. To investigate the practical effect of BFT in the tilapia ponds, thethesis studied the impact of different carbohydrates addition on water quality and tilapiagrowth performance, and water quality was analyzed using factor analysis approach.The main results of this research were as follows:1. This experiment studied the water quality, fish （new GIFT tilapia） growth andfeed utilization when fish were fed with different amount of feed and wheat starch wasadded. Fish were kept in12outside cemented ponds. The control group was fed withcommercial feed normally, while group A, B and C were fed100%,80%and75%ofnormal amount of feed and added with wheat starch （30%of total feed in weight）.Water samples were taken to measure pH, DO, T, Secchi disk depth（SD）, total ammonianitrogen （TAN）, nitrite nitrogen （NO2--N）, nitrate nitrogen （NO3--N）, total nitrogen（TN）, total phosphorus（TP）, chlorophyll-a（Chl.a）, floc volume（FV）, total suspendedsolids（TSS） and total heterotrophic bacterial （THB） every week, and the growthperformances, feed conversion ratio （FCR） and protein efficiency ratio （PER） wereanalyzed after harvest. The results showed that the addition of wheat starch increasedthe content of FV, TSS and THB while reduced the concentrations of TAN （significantlyin group C）, NO2--N, NO3--N, TN, TP and Chl.a. The weight gain rate （WGR） andspecific growth rate （SGR） in group A were higher than these in the control group （P>0.05）. Compared to the control group, group B and group C showed no significantdifference in fish growth performance, while had significantly lower FCR（12.96%and17.04%decreased in group B and C respectively） and higher PER （14.91%and21.04%increased respectively （P<0.05））. In summary, the addition of wheat starch reduced theconcentration of the inorganic nitrogen thus improved water quality, and producedbiofloc used by tilapia thus reduced FCR.2. Mannose-oliogosaccharides （MOS） has been paying more attention by people asa new feed additive in aquaculture, which is also a kind of simple carbohydrate. Theexperiment studied if MOS could be used as carbohydrate in tilapia BFT system underacceptable cost condition. Fish（new GIFT tilapia） were kept in12outside cementedponds. The control group was fed with commercial feed normally, while group A, B andC were fed75%of normal amount of feed and added with MOS （2%,4%,6%of totalfeed in weight respectively）. Water samples were taken to measure pH, DO, T, SD, TAN,NO₂--N, NO₃--N, TN, TP, Chl.a, FV, TSS and THB every week, and the growthperformances, FCR and PER were analyzed after harvest. The results showed that thedecrease of feed and addition of MOS reduced the concentrations of TAN, NO3--N, TN（P<0.05）, NO2--N, TP, and THB （P>0.05）. There were no obvious variation between FVand TSS in all treatments. Compared to the control group, group A, B and C showed nosignificant difference in survival rate, FCR and PER, while had significantly lowerWGR and SGR. In summary, the decrease of feed and addition of MOS didn’t promotethe multiplication of heterotrophic bacteria and the generation of floc, and limitted thegrowth of fish. So, we verified that MOS isn’t suitable for carbohydrate in BFT system.3. There are many water quality parameters in aquaculture, the relationship ofwhich is complicated. Finding a few monitoring parameters is the practical needs offarmers. Factor analysis is, an extent to principal component analysis, a statisticalmethod that expresses the complicated information by using few representative factors.In this experiment using this method the water quality in chapter2was evaluated.Correlation analysis showed that physical and chemical factors were significantlycorrelated with each other, but no simple linear relationships. Factor analysis revealedthat three factors extracted could sufficiently cover most of the information whendissolved oxygen was enough. The first mian factor contributed52.021%, whichrepresented organic nutrients, consposing of TP, Chl.a and TN. The second main factor contributed20.526%, which represented inorganic nitrogen and SD, consposing of TAN,SD, NO2--N and NO3--N. The third factor contributed12.579%, which composed of FV.The synthetic score of each pond showed that biofloc technology could improve waterquality and promote the sustainable development of tilapia culture. TN, TP and Chl.ashould be monitored emphatically in tilapia culture systems using biofloc technology.The culture effect is good when tilapia were fed75%of normal amount of feed andadded with wheat starch （30%of total feed in weight）, and the concentration of TN, TPand Chl.a should be controlled emphatically in culturing period. This not only offeredsome theory references for low-carbon and healthy tilapia culture, but also providedaquaculture production and management with practical guidance.