The practice of polyculture in aquaculture has led to increased production. However, there is a need to develop a suitable culture scheme in order to optimize production. This paper evaluates the production and economic feasibility of the polyculture of two commercially important species, the blue swimming crab (Portunus pelagicus Linnaeus 1758) and red seaweed (Kappaphycus alvarezii Doty). Blue swimming crabs (initial weight 43.0 ± 1.4 g, CW 9.1 ± 0.4 cm) and red seaweeds were cultured in 1m3 cage for 45 days. For crab production evaluation, 10 crabs were placed in a cage with varying seaweed stocking density: 10 + 500 (g red seaweed), 10 + 750 and 10 + 1,000. Treatment without red seaweeds (10 + 0) served as the Control. For seaweed production, two culture schemes (hanging and bottom method) were evaluated with the same stocking density used in crabs. However, set-up with 1,000 g red seaweed and without crab (0 + 1,000) served as Control. Each treatment consisted of five replicates. Stock sampling and determination of production parameters were done every 15 days until the end of the culture period. Production evaluation included specific growth rate, survival rate and net production while economic evaluation included computation of the ROI (Return on Investment) and payback period of the polyculture system as a whole. For crabs, highest net production (P< 0.05) was obtained in the 10 + 750 treatment. For seaweed production evaluation, the bottom culture scheme showed significantly higher (P < 0.05) net production and SGR. Further, red seaweeds cultured in the 10 + 750 showed highest net production (P < 0.05) among the stocking density combination evaluated. ROI was computed to be 40% and the payback period is 2.5 years. The study suggests polyculture of blue swimming crab and red seaweeds using the bottom culture scheme at 10 + 750 as the optimum stocking density.
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