article · Animals
This study examined the effects of stocking density and dietary carbon sources on the physiological condition, oxidative status, and immune responses of Nile tilapia reared in biofloc systems. Fish were stocked at either low density (140 fish per cubic metre) or high density (280 fish per cubic metre) in units containing water without added carbon, or with glycerol, molasses, or starch. Fish in control groups showed reduced red blood cell counts, haemoglobin, and haematocrit, alongside the highest stress indicators, including glucose and cortisol. Biofloc groups displayed higher monocyte percentages. Starch at high density significantly increased total serum protein, albumin, and globulin levels. Glycerol at low density yielded the highest antioxidant enzyme activities, including superoxide dismutase, glutathione reductase, and catalase. Molasses significantly upregulated immune-related genes, indicating that molasses improves the overall health status of Nile tilapia in biofloc systems.
High stocking densities in aquaculture often induce severe physiological stress and disease vulnerability in fish. This research demonstrates that adding carbon sources such as molasses, starch, or glycerol into biofloc water mitigates stress, enhances antioxidant defences, and boosts immune function in Nile tilapia. These findings help aquaculture operators select tailored carbon inputs to improve fish welfare and survival in intensive rearing facilities.
This research represents applied, tested work relevant to commercial aquaculture operators and biofloc farm managers. The findings demonstrate practical water-management interventions using accessible carbon inputs to support fish health under dense stocking conditions. Because standard inputs like molasses and starch were evaluated under realistic operational densities, the practices are near-market and could be adopted directly into commercial intensive tilapia farming protocols, subject to site-specific cost analyses.
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The present study investigated the effect of stocking density and dietary carbon sources on the water quality, oxidative status, and immune-related genes of Nile tilapia (<i>Oreochromis niloticus</i>) reared under biofloc conditions (BFT). Eight groups were established at two levels of stocking densities (140 fish per m<sup>3</sup>: low stocking density, LSD) and (280 fish per m<sup>3</sup>: high stocking density, HSD) (5.15 ± 1.12 g) and kept in eight biofloc units containing water without carbon sources (control groups) or with glycerol, molasses, or starch. Red blood cells count, hemoglobin, and hematocrit values were reduced in fish stocked in control groups at LSD and HSD than biofloc groups. Control fish groups reared at both LSD and HSD have the highest significant (<i>p</i> < 0.05) white blood cells number than other fish groups. Meanwhile, fish groups that received glycerol, molasses, and starch maintained in both LSD and HSD presented a higher significant (<i>p</i> < 0.05) monocyte % than in the control group reared at both LSD and HSD. The fish group reared in biofloc conditions (BFT) using starch carbon source and reared at the HSD presented a significantly higher (<i>p</i> < 0.05) increase in total serum protein and albumin levels as well as globulin value than the control fish group reared at both LSD and HSD. The highest glucose and cortisol levels were showed in the control fish group reared at both LSD and HSD. Fish maintained in glycerol-based biofloc at LSD attained the highest (<i>p</i> < 0.05) serum superoxide dismutase (SOD), glutathione reductase (GR), and catalase than other experimental groups. Regarding the nonspecific immune status, significantly increased expression of CC-chemokines, CXC-chemokines, TLR7 and IL-8 genes was found in molasses based biofloc groups. The data of the present study revealed that using molasses promotes health status of Nile tilapia cultured in a biofloc system.
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DOI: 10.3390/ani11010184
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