3. Results and discussion
3.1. Water quality
Daily changes in the water quality parameters are shown in Table 1.
There were no significant differences in temperature (29.8–23.0 °C) or
pH (7.98–6.48) between the two groups (P N 0.05). DOwasmaintained
at a level greater than 6 mg L−1
, and differed significantly between
the two groups (P b 0.05). This likely resulted from the higher respira-
tion rates caused by the bacteria and other microorganisms in the BFT
group. Similar results were reported in other studies (Emerenciano
et al., 2012; Kim et al., 2014). However, the DO level in the BFT
treatment was well within the acceptable range for the survival and
growth of fish.
The fluctuation of TSS over time is presented in Fig. 1.TheTSS
levels in the BFT treatment increased gradually throughout the experi-
mental period. The average TSS concentration was 24.61 mg L−1
in the control group and 484.48 mg L−1
in the BFT treatment. As
demonstrated by Ray et al. (2010), the TSS concentration in the BFT
tanks should be well controlled because it is closely related to water
quality and anti-clogging of fish gills. In our study, we attempted to
maintain the TSS level below 400 mg L−1
. Although we removed
some water from the light-limited BFT tanks and replaced it after
removing most of the floc using buckets, the TSS levels reached almost
1000 mg L−1
in the last two weeks. This uncontrollable situation was
also reported by Azim and Little (2008) for light-limited BFT systems.
However, no apparent negative influence on fish survival or growth
was observed in the BFT group throughout the experiment.
Avnimelech (2012) demonstrated that in the case of fish ponds, TSS
concentrations can reach levels of up to 1000 mg L−1
,andthelevel
should be limited to approximately 400 mg L−1
, though data that indi-
cate this level are lacking. Moreover, in tilapia culture, Avnimelech
(2007) reported values ranging from 460 to 643 mg L−1
, while Azim
and Little (2008) presented average levels of 597 and 560 mg L−1
.