The 12.5:1 fixed C/N ratio by dextrose input in all experi- mental groups was able to maintain the TAN mean level near to 1 mg L−1 until the day 5 when this parameter have steadily started to increase in the two higher densities groups (D300 and D350) (Fig. 1A). Free ammonia increased somewhat on the last two days of the experiment following the same profile of TAN (Fig. 1B). How- ever mean values of total and free ammonia remained below toxic levels throughout the experimental period (Cobo et al., 2012).