Sustainable aquaculture in oxbow lakes: insights from polyculture practices in Vandardaho Baor

Abstract

Vandardaho Baor, a prominent oxbow lake in Chuadanga district of southwestern Bangladesh, offers substantial opportunities for sustainable aquaculture through polyculture practices. This study investigates the current polyculture systems practiced in the baor, focusing on fish productivity, environmental conditions, and socio-economic outcomes for local communities. The officially recorded and GPS-verified surface area of the baor is 100 hectares according to the Department of Fisheries (DoF, 2018) and field verification (2025). Seasonal contraction during the dry period reduces visible water spread to approximately 85 hectares, which explains earlier discrepancies in area reporting. Fieldwork included sampling of water quality parameters (DO: 6.2 ± 0.6 mg l^-1, pH: 7.4 ± 0.3, temperature: 28-31°C, Transparency: 32-38 cm), along with ammonia (0.04 mg l^-1), nitrate (0.18 mg l^-1), phosphate (0.12 mg l^-1), alkalinity (110 mg l^-1), hardness (140 mg l^-1), and biological oxygen demand (BOD: 2.1 mg l^-1), fish species composition, and economic data from 45 fish farmers. The results showed that polyculture-primarily involving Rohu (Labeo rohita), Catla (Catla catla), Mrigal (Cirrhinus cirrhosus), Silver Carp (Hypophthalmichthys molitrix), and Tilapia (Oreochromis niloticus)-yielded an average of 4,015 ± 225 kg ha^-1 yr^-1, which is 35% higher than nearby monoculture systems. Independent sample t-test confirmed that the mean yield difference between polyculture (4,015 ± 225 kg ha^-1) and monoculture (2,745 ± 195 kg ha^-1) was statistically significant (t = 6.28, p < 0.001, 95% CI = ±82 kg). Farmers practicing polyculture earned an average net income of BDT 149,200 ± 13,450 per hectare annually, significantly higher than monoculture income (BDT 97,800 ± 11,200; p < 0.001).Additionally, biodiversity was better maintained (Shannon-Wiener Index H' = 2.36 in polyculture vs 1.71 in monoculture), and disease outbreaks were relatively low due to species compatibility. However, the study identified constraints such as irregular water exchange, poor access to quality feed and fingerlings, and lack of training in modern aquaculture techniques. The findings underscore the importance of targeted policy support, technical training, and community-based management to enhance the sustainability and productivity of polyculture in Vandardaho Baor.