Use of two freshwater macrophytes, water hyacinth ( Eichhornia crassipes ) and coontail ( Ceratophyllum demersum ), as carbohydrate sources in biofloc system for Nile tilapia ( Oreochromis niloticus )

Abstract

Two freshwater macrophytes, water (Eichhornia crassipes) and coontail (Ceratophyllum demersum), were evaluated as carbon sources in biofloc system for Nile tilapia (Oreochromis niloticus), in comparison with molasses and a RAS with 10% water exchange daily (control). All-male tilapia (9.35 g) were stocked in 70-L fibreglass tanks at 10 fish tank−1 and fed on a commercial diet (30% cp) for 60 days. The average water temperature, pH and dissolved oxygen (DO) did not significantly differ (p > 0.05) among all treatments. Total ammonia–nitrogen (TAN) was significantly lower in the control group (0.11 mg L−1) than in biofloc treatments (0.15–0.17 mg L−1). Nitrite (NO2–N) concentrations were significantly lower, while nitrates (NO3–N) higher, in biofloc-based treatments (20.23–25.77 mg L−1) than in the control group (12.85 mg L−1). Biofloc volume (BFV) (28.17–33.50 ml L−1) and total suspended solids (TSS) (691–824 mg L−1) were not significantly different among molasses and macrophytes treatments. The control group displayed lower growth rates and feed efficiency than macrophytes-based groups. Blood parameters, immunological responses, digestive enzymes activities, liver function enzymes and upregulation of IFN-γ, TNF-α and IL-8 genes were significantly better in molasses- and macrophytes-treated tanks than the control group. These results suggest that water hyacinth and coontail can be used as costless, eco-friendly carbon sources in biofloc systems.