Biofloc technology is a sustainable aquaculture strategy that enhances nutrient recycling and water quality. However, optimizing the carbon-to-nitrogen (C/N) ratio is essential for maximizing production efficiency. This study evaluated the effects of four C/N ratios (10:1, 15:1, 20:1, and 25:1) on growth performance, feed utilization, carcass traits, whole-body proximate composition, water quality, biofloc characteristics, and economic efficiency of sex-reversed climbing perch (Anabas testudineus) cultured in biofloc systems. Fish were reared for 8 weeks in a completely randomized design with 4 treatments and 3 replicates per treatment. The C/N ratio significantly affected growth performance, feed utilization, carcass traits, biofloc characteristics, several water quality parameters, and production cost (p<0.05). Fish cultured at C/N 20:1 achieved the highest final weight (15.94±0.77 g) and the lowest feed conversion ratio (1.82±0.02), together with favorable water quality and the lowest total feed and carbon cost (1.41±0.04 USD kg-1 of weight gain). Although C/N 25:1 produced the highest floc volume and total suspended solids, C/N 20:1 resulted in the most favorable overall growth and feed utilization performance among the tested treatments. Overall, among the tested C/N ratios, 20:1 provided the most favorable balance between microbial activity, nutrient utilization, water quality, fish performance, and economic efficiency, supporting sustainable biofloc-based culture of sex-reversed climbing perch.
