Probiotic-Enriched Biofloc Enhances Water Quality, Growth, Feed Utilisation, and Disease Resistance of Rohu (Labeo rohita) at Different Stocking Densities under Indoor Conditions

Abstract

This study evaluated the effects of probiotic enriched biofloc technology (BFT) on water quality, proximate composition of biofloc, growth performance, feed utilisation, and disease resistance of rohu (Labeo rohita) cultured at different stocking densities under indoor conditions. A 2 × 3 factorial design was employed with two culture systems—biofloc with probiotics (BP) and biofloc without
probiotics (BWP), and three stocking densities (20, 23, and 26 fish m^-2), each in triplicate, for 90 days using fish with an initial average weight of 3.06 ± 0.15 g. Proximate composition of biofloc revealed significantly higher crude protein (33.42 ± 0.94% vs. 31.38 ± 1.05%), crude fat (6.68 ± 0.47% vs. 5.34 ± 0.32%), and crude fibre (3.83 ± 0.05% vs. 2.89 ± 0.10%) in BP compared to BWP (p < 0.05). Water quality remained stable, with ammonia levels within safe limits (0.01–0.02 ± 0.01 mg L^-1) and higher dissolved oxygen concentrations (7.13–7.38 ± 0.31 mg L^-1) in BP groups. Growth performance was markedly enhanced in BP treatments, with final body weight (123.37 ± 3.39 g vs. 57.70 ± 2.26 g), specific growth rate (0.95–0.99 ± 0.02% d-1 vs. 0.45–0.54 ± 0.01% d-1), survival (73.33 ± 1.45% vs. 26.67 ± 1.76%), and feed conversion ratio (2.21–2.83 vs. 3.20-4.50) showing significant differences (p < 0.05). Following intraperitoneal challenge with Aeromonas hydrophila, histopathological examination further confirmed the protective role of probiotics, with BP fish exhibiting preserved intestinal villi, reduced goblet cell hyperplasia, and limited renal tubular degeneration and inflammatory infiltration, whereas BWP fish displayed villus erosion, bacterial colonisation, tubular necrosis, and glomerular dilation. Overall, probiotic-enriched biofloc improved biofloc nutritive value, stabilised water quality, enhanced growth and feed utilisation, and provided effective protection against A. hydrophila challenge. These findings highlight probiotic biofloc as a sustainable and cost-effective strategy for intensifying freshwater aquaculture while improving fish health, renal integrity, and overall resilience.