Polyculture of the sea cucumber (Holothura scabra) with tiger shrimp for water quality improvement.
Abstract This case study describes research on the polyculture of the sandfish (Holothuria scabra) and tiger shrimp (Penaeus monodon) to improve pond water quality. At the first location in Khanh Hoa province, three 1,200-m2 ponds were stocked with shrimp postlarvae (PLs) at a density of 30 PLs m-2. Two ponds (S4 and S3) were stocked with sandfish, at 50 and 100 g m-2, while no sandfish was stocked in the control pond (S2). At the second location also in Khanh Hoa province, three 450-m2 ponds were constructed and stocked with shrimp PLs at a density of 30 PLs m-2. Two of these ponds (S5 and S6) were stocked with sandfish at 50 and 100 g m-2, while no sandfish was again stocked in the control pond (S7). A higher stocking density of sandfish generated a higher growth rate of shrimp (one -way ANOVA, p=0.15, n= 50). The growth rate of shrimp increased with sandfish stocking density, from 0.036 to 0.057 to 0.067 g per day at sandfish stocking densities of 0, 50 and 100 g m-2, respectively. Increasing sandfish stocking density also reduced the hydrogen sulphide (H2S) concentration (one-way ANOVA, p<0.05, n=89). Likewise, concentrations of nitrite (NO2-N), and total organic compounds were higher in systems not stocked with sandfish (one-way ANOVA, p<0.05, n=50). Fungal and bacterial densities decreased with increasing sandfish stocking density. This study thus showed that sandfish could remove certain quantities of toxic gases, organic compounds and microorganisms from shrimp culture systems.