Assessing Yield Performances and Economic Profitability of Integrated Nile Tilapia ( <i>Oreochromis Niloticus</i> Linnaeus, 1758) With Bombay Red Onion ( <i>Allium cepa</i> ) Farming Systems in Northwest Ethiopia

ABSTRACT Integrated fish–vegetable is a sustainable food production strategy that synergistically combines fish culture and vegetable cultivation within a single farming system. The objective of this study was to assess integrated Nile tilapia–onion (Bombay red variety) production in northwest Ethiopia, as both fish and onion are commonly practiced by smallholder farmers. The experiment was designed with three fish stocking density levels, low, medium and high, at 3, 5 and 7 fish/m 2 , respectively, in nine geomembrane‐lined ponds with a volume of 72 m 3 each for a 180‐days experimental period. A total of 24 onion plots were integrated with fishponds water under each stocking density with and without chemical fertilizers, while river water with and without chemical fertilizers served as comparative treatments. Results revealed significant enhancement in both fish and onion production and economic profitability across all treatments ( p &lt; 0.05), with the highest stocking density consistently delivering superior performance. Fish reared under high stocking density (HSD) achieved 58%, 88.5% and 66.7% higher gross yield (kg/ha), net profit ($/ha) and water‐use efficiency (kg/m 3 ), respectively, than those under low stocking density (LSD). Similarly, onion irrigated with fishponds water outperformed non‐integrated farming, producing 42% (without chemical fertilizers) and 55% (with chemical fertilizers) higher marketable yields, 1.5 times (without chemical fertilizers) and 1.7 times (with chemical fertilizers) higher water‐use efficiency, and 11 times (without chemical fertilizers) and 13 times (with chemical fertilizers) higher net profits ($/ha). Nile tilapia at HSD level (7 fish/m 2 ) integrated with onion maximizes productivity, profitability and water‐use efficiency, highlighting potential for policy support and extension promoting sustainable intensification, income diversification and climate‐resilient livelihoods in north‐western Ethiopia.