2. Bioflocs as a Nutritious Food Source, for Dietary Protein Reduction, Compensatory
Growth, and Productivity of Economically Important Aquatic Species
Bioflocs as a Nutritious Feed Source
One of the major challenges facing aquaculture producers is the high cost of aqua-
culture feeds. Protein levels and adequate amino acid balance are critical in aquaculture
feeds due to their essential role in maintaining the growth and the general wellbeing of
aquatic organisms. However, these nutrients are an expensive component of the feeds and
hence influence their market price [
33
]. In tilapia, for example, feeding can account for
50% of the operational costs and could even reach higher levels with high-protein diets
and/or inadequate protein [
33
,
34
]. However, this could be mitigated by feeding tilapia on
alternative feed sources such as phytoplankton, zooplankton, and algae, whose nutritive
content would enhance the growth, survival, and production of fish [
35
]. Avnimelech and
Kochba [
36
] found that tilapia can uptake 240 mg N kg
−1
of biofloc, which is equivalent to
25% of the protein in fish diets. Moreover, bioflocs can contain 20%–<40% crude protein,
<1%–>8% lipids, <1%–>15% fiber, <18–>35% total carbohydrates, and <15%–>60% ash,
thus providing an alternative feed source to the reared aquatic species [
2
].
It is worth noting that the nutritional value of bioflocs is highly dependent on the
microbial community that encompasses it and, as mentioned in the previous section, certain
factors such as carbon sources and C/N ratio influence the biochemical composition of
bioflocs. For example, Moreno-Arias et al. [
37
] reported that the fatty acid and amino acid
composition of both biofloc and shrimp cultivated in BFT systems depends on the composi-
tion of the aquaculture feed used. The use of plant-based protein sources in the feed is more
favorable for biofloc systems and is considered to be more eco-friendly and sustainable.
This is because their use reduces the release of phosphorous and nitrogenous wastes in
the aquatic ecosystem as well as the dependency on overexploited marine sources [
14
,
38
].
The effect of biofloc feed on the general wellbeing and sustainable production of aquatic
species is discussed below.
Emerenciano et al. [
39
] investigated the influence of BFT as a food source in a limited
water exchange nursery system on the growth performance of pink shrimp (Farfantepenaeus
brasiliensis) post-larvae. The authors reported that rearing post-larvae in the BFT system
without commercial food supply did not affect the growth performance of the animals.
Moreover, no significant differences in final biomass and weight gain were noted between
shrimp reared in BFT with or without commercial diet supplementation. The good growth
performance of the larvae was attributed to the diverse microbial community that consisted
of protozoa grazers, rotifers, cyanobacteria, and diatoms, which were utilized as a food
source. In another study, Emerenciano et al. [
40
] found no significant differences in the final
biomass and survival of early post-larvae pink shrimp (Farfantepenaeus paulensis) reared
in BFT with or without commercial feed supplementation. Emerenciano et al. [
11
] also
observed no significant difference in spawning performance among females reared in BFT
with or without feed supplementation. Zhang et al. [
10
] found that culturing gibel carp
(C. auratus gibelio
♀
×
C. carpio
♂, 6.4
±
0.5 g) in BFT without feed addition for 30 days did
not affect the growth performance (weight gain, specific growth, and survival) of fish. The
fish were able to utilize the bioflocs as a feed, with increased digestive enzyme activity of
pepsin and amylase noted in fish reared in water containing high TSS (300, 600, 800, and
1000 mg L
−1
TSS). Furthermore, bioflocs enhanced the fish’s innate immunity, as indicated
by increased superoxide dismutase (SOD) and total antioxidant capacity (TAOC) activity
in the skin and mucus. Upregulated immune-related genes included intelectin (ITLN),
dual-specificity phosphatase 1 (DUSP 1), keratin 8 (KRT 8), myeloid-specific-peroxidase
(MPO), c-type lysozyme (c-lys), and interleukin-11 (IL-11).
The nutritive content and quality of bioflocs are rich and, as such, bioflocs have
been used as a cheaper and sustainable alternative to the highly expensive fishmeal. For
example, in shrimp culture, 15% to 30% of conventional protein sources can be replaced
Sustainability 2021, 13, 7255
5 of 15
by biofloc meal without negatively affecting the general wellbeing of the species [
2
]. The
incorporation of biofloc meal in aquaculture indeed reduces the costs of production whilst
permitting an intensive culture of species, hence maximizing profits. Several studies have
shown that replacing fishmeal with biofloc meal alone or in combination with certain
dietary sources such as lysine, soy protein concentrate, and protein hydrolysate improves
the growth performance, survival, digestive enzyme activity, and immunity of the reared
aquatic species [
41
–
48
].
Currently, more research studies in the field of pro- and prebiotic bioflocs are ongoing.
Probiotics are beneficial microbes that are either added or naturally developed in the BFT
system to stimulate the immune system for the reared aquatic species against biotic and
abiotic stress. Several beneficial microorganisms, such as those from the Bacillaceae family,
have been previously identified and isolated from the shrimp culture BFT system [
49
].
These bacteria have been used in the biocontrol of disease outbreaks caused by pathogenic
microbes as well as immunostimulants for enhancing the general wellbeing of aquatic
species. Table
1
shows some of the conducted studies on probiotics in BFT systems included
in animal diets or added directly into the rearing water for enhancement of the general
wellbeing of the reared aquatic species.
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