Pond-Based IMTA Improves Productivity, Environmental performance and Sediment Organic Matter in Coastal Kenya

Integrated multi-trophic aquaculture (IMTA) offers a climate-smart approach for improving aquaculture productivity while reducing organic enrichment in coastal pond systems. This study evaluated a marine tilapia pond-based IMTA pilot across Kwetu, Kibokoni and Tsunza fish farming sites in coastal Kenya, comparing monoculture controls, tilapia + gastropod (Terebralia spp.; T+G), tilapia + sea cucumber (T+S), and full IMTA with tilapia, Terebralia spp. and sea cucumber (T+G+S). Fish growth was monitored monthly using 50 fish per pond per sampling event, while sea cucumber and Terebralia spp. were assessed using 20 individuals per pond. Water quality was monitored weekly for 29 weeks, and sediment organic matter was assessed during two sampling rounds. Initial fish mean weights were comparable across treatments, approximately 3.8 g, but final mean weight differed significantly (ANOVA: F(3,8)=43.29, p<0.001), increasing from 289.0±3.6 g in monoculture controls to 358.3±13.5 g in full IMTA, representing a 24.0% gain. Sea cucumber and Terebralia spp. also performed better in full IMTA than in their respective two-species treatments. The economic assessment indicated that full IMTA generated the highest gross return, net return and benefit–cost ratio, which improved from 1.30 in monoculture controls to 1.59 in full IMTA. Weekly water quality showed more stable pond conditions in full IMTA, including higher dissolved oxygen than controls (4.86±0.33 versus 4.32±0.32 mg L⁻¹; F(3,344)=43.82, p<0.001). Sediment organic matter was consistently lower in full IMTA than controls, with a strong treatment effect (F(3,80)=333.94, p<0.001). Benthic and plankton assemblages showed site- and treatment-specific restructuring, suggesting organic matter processing and trophic modulation. These findings demonstrate that pond-based IMTA can increase multi-trophic productivity, improve environmental performance, reduce sediment organic loading and strengthen farm-level profitability in coastal Kenya.