Figure 1. Schematic diagram of a biofloc technology system.
1.1.1. Carbon–Nitrogen Ratio
In the aquatic environment, the carbon–nitrogen ratio (C/N) plays a vital role in the
immobilization of toxic inorganic N compounds into useful microbial biomass that might
act as a direct source of food for the reared aquatic species. Immobilization of inorganic N
occurs at a C/N ratio of organic matter above 10 and, hence, any alteration in this ratio
within the BFT system might result in a shift in microbial diversity, which might further
affect the water quality. For example, De Schryver et al. [13] observed that a high C/N
ratio favors the proliferation of heterotrophic bacteria, which leads to significant changes
in water quality and biofloc composition. As such, manipulation of the C/N ratio can be
achieved through modification of the carbohydrate content in the feed or the addition of
an external carbon source in the rearing water so that microbes can assimilate waste am-
monium for microbial biomass production. This will, in turn, decrease the concentrations
of ammonium/ammonia to less toxic levels, thus making water exchange unnecessary
[14]. Total suspended solids (TSS) is another important water quality parameter whose
concentration in aquatic ecosystems depends on the C/N ratio. Xu et al. [15] observed that
a high C/N ratio (15:1 and 18:1) rapidly increased the TSS concentrations in water, which
negatively affected the growth performance of L. vannamei. Moreover, the authors antici-
pated that production costs would be reduced under the C/N ratio of 12:1 compared to
15:1 and 18:1 due to reduced utilization of organic carbon, saving approximately 20,000 L
of molasses per hectare of shrimp production at the same stocking density. Pérez-Fuentes
et al. [16] also found that, under high-density cultivation of O. niloticus in a BFT system,
C/N ratios exceeding 15:1 promoted the production of dissolved salts and settled biomass,
which affected the growth performance of fish. The authors recommended a C/N ratio of
10:1 as the optimum condition for the production of O. niloticus reared under similar con-
ditions. In another study, Silva et al. [17] also observed poor water quality (high TSS, tur-
bidity, alkalinity, and settleable solids) at a C/N ratio of 20:1, which affected the growth
performance of O. niloticus. Similar results have been reported in Clarias gariepinus [18,19].
However, Yu et al. [20], Haghparast et al. [21], and Wang et al. [22] reported better growth
performance and immune stimulation in carp at high C/N ratios (20:1 and/or 25:1) reared
Chia sẻ với bạn bè của bạn: |