Portioning of microbial waste into fish nutrition via frugal biofloc production: A sustainable paradigm for greening of environment

The goal of this study is to see whether biofloc technology (BFT) is suitable to grow Ompok bimaculatus (pabda) seeds. The experiment compared four levels of C/N ratio maintained using an exogenous carbon source, namely C/N10 (1.7 mL/L), 15 (6 mL/L), 20 (13.0 mL/L), and 25 (14.6 mL/L), to a control (0.0 mL/L) without any carbon addition. Pabda larvae (0.082 ± 0.001 g) were raised for 45 days in BFT 50 L glass aquaria. The effects of BFT with different C/N ratios on system water & floc quality, as well as on animal performance, feed utilization, and flesh quality, were studied. In comparison to the control, the results showed that BFT could effectively manage nitrogenous waste in the system. The BFT group had better nitrogen retention in stock biomass, with C/N20 (40.34%) having the best performance. Factor analysis revealed the dominance of the heterotrophic population in the system. The floc volume increased as the C/N ratio increased, however the size decreased. The level of floc protein decreased (p < 0.05) as the C/N ratio increased. BFT groups outperformed control groups in terms of growth, survival, and condition factor (p < 0.05), with C/N20 performing best. In addition, C/N20 noted a significant (p < 0.05) difference in feed conversion ratio (FCR) and protein efficiency ratio (PER) as compared to control. In the liver, gut, and muscle tissues, digestive enzymes such as amylase, lipase, and protease were higher in BFT, compared to control. Gut morphology was better in BFT groups (p < 0.05), with C/N20 showing increased height, width, and absorptive area of microvilli. The overall conclusion of this study is that varying C/N in the BFT system has an impact on system water quality, animal performance, feed utilization, floc characteristics, digestive function, and gut morphology. This research explains on how to use BFT as a long-term solution for in-situ waste conversion to reduce effluent load for pabda seed production. The study suggested a way not only for effective utilization of nutrient-enriched biofloc as nutritious feed supplements, but also paved the way for water conservation along with the safe conversion of microbial biofloc into fish nutrition for facilitating a clean environment.