2.5. Water quality
Water quality was monitored to ensure that it remained within
healthy ranges for both species; water parameters were measured and
analyzed in both recirculating systems. Water temperature, dissolved
oxygen (DO) and pH weremeasured 3 times aweek in themorning before
the first feeding (Monday, Wednesday and Friday, 8:00 to 9:00 h)
and 3 times in the afternoon after the last feeding (Tuesday, Thursday
and Saturday, 16:00 to 17:00). Temperature and DO were measured
with a digital meter (YSI model 85) and pH with a multiparameter
tester (35 Series Oakton Eutech instruments). Total ammonia nitrogen
(TAN), nitrite nitrogen (NO2-N) and total alkalinity were sampled
every week and analyzed with a Hach test kit (model FF-1A).
2.6. Statistical analyses
Growth performance parameters were analyzed through a twoway-
ANOVA, using tilapia population (mixed-sex and 95% males) and
species proportion (3:1, 5:1, 7:1 and 1:0) as factors.When the ANOVA
result from a dependent variable indicated significant differences
(P b 0.05), these were tested with the Tukey multicomparison test of
means, using a significance level of P b 0.05. Survival (%) data were
normalized using the arcsine of the square root transformation. Fish
condition factor and FCR were transformed to ranks. The analyses
were run using the InfoStat v.2008 statistical package.