3.Results
3.1. Larval growth performance
The survival of the larvae originating from the BFT broodstock tank was higher than for the larvae originating from the control tank,
regardless of the type of water in which they were housed (Table 1). No significant differences between the treatments were observed in termsofspecificgrowthrateandtheconditionfactor.Therelativestandarddeviationthatrepresentsthevariabilityofthefishtotallengthwas lower in case the larvae were reared in BFT water. The difference was significant with larvae originating from the BFT broodstock tank. No significant interaction between the origin of the larvae and the larvae culturewaterwasobservedforanyofthegrowthparametersmeasured in this study. ThepostchallengesurvivaloftilapialarvaeoriginatingfromtheBFT broodstock tank was significantly higher than those originating from the control broodstock tank (P = 0.044) (Fig. 1). The culture water in which the larvae were housed, however, did not significantly affect thesurvivalpostchallenge(P=0.245).Interestingly,thepostchallenge survival of larvae from the C/BFT treatment was also 36% higher than that of larvae from the C/C treatment. No significant interaction was observed between the origin of thelarvae and thelarvae culture water (P= 0.472).
3.2. Water quality parameters
The water temperature and DO levels were similar in all tanks during the growth test (Table 2). Significantly lower alkalinity concentrationswereobservedinthetankswithcontrolwater.Totalammoniacal nitrogen concentrations were significantly lower in the tankswithBFTwaterthaninthosewithcontrolwater.Nitrite-Nconcentrations seemed tovaryrandomly accordingtotypeof water and origin of the larvae. No significant differences were observed for the nitrate-N concentrations.
3.3. Salinity stress test
Onehour afterthesalinitystress,asignificantlyhighersurvivalwas observed for the larvae originating from the BFT broodstock tank than for the larvae originating from the control broodstock tank (Fig. 2). After 24 h in freshwater, an additional 30% mortality was observed for both treatments. However, the number of survivors among the larvae originating from the BFT tankwas still significantly higher than for the larvaeof control origin.
4. Discussion
Theconditionsunderwhichbrood fisharerearedhavebeenreportedtosignificantlyinfluencethelarvalqualityandquantity(Gunasekera etal.,1996).Biofloctechnologyapplicationhasbeenshowntoimprove
Table 1 Mean(±standarddeviation)oftheperformanceparametersofNiletilapialarvae(n=4).Valueswithinthesamerowmarkedwithdifferentsuperscriptlettersaresignificantlydifferent (P b 0.05).The P valuesresulting from thetwo-way ANOVA analysisare presented inthelast threecolumns.
BFT/BFT BFT/C C/BFT C/C P-value larval origin
P-value rearing system
P-value interaction of larval origin and rearing system Final ABW (mg) 108 ± 15a 112 ± 44a 119 ± 24a 105 ± 18a 0.891 0.712 0.515 Final ABL (mm) 16.6 ± 1.2a 16.2 ± 1.3a 17.3 ± 0.7a 16.4 ± 1.3a 0.394 0.293 0.689 SGR (%/day) 12.0 ± 1.0a 10.9 ± 2.2a 11.7 ± 1.5a 10.8 ± 1.2a 0.736 0.308 0.200 CF (k) 2.4 ± 0.4a 2.3 ± 0.4a 2.3 ± 0.4a 2.4 ± 0.4a 0.507 0.537 0.855 RSD total length (%) 10.6 ± 1.6a 14.7 ± 1.4b 12.2 ± 4.8ab 14.2 ± 1.1b 0.744 0.032 0.486 Survival (%) 98 ± 3a 90 ± 9ab 67 ± 9c 75 ± 15bc 0.000 0.455 0.066 ABW: averagebodyweight. ABL: average body length. SGR: Specific growth rate. CF: condition factor. RSD total length:relativestandarddeviation ofthetotal length. BFT/BFT: fish larvaecollected from theBFT broodstock tankand transferredto BFT water. BFT/C: fish larvaecollected from theBFT broodstock tank andtransferred to control water. C/BFT: fish larvaecollected from thecontrolbroodstock tankand transferred to BFT water. C/C: fishlarvaecollectedfrom thecontrol broodstock tankand transferredto control water.
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