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The sustainability of prawn farming in brackish water ponds is controversial because of low yields and a history of mangrove clearing. Low yields are due largely to insufficient preparation of pond bottoms. Mangrove trees are often planted on pond bunds as window dressing. This study examines the effect of three types of liquid compost from vegetable, fruit, and both vegetable and fruit in tanks to which whole or chopped Avicennia marina leaves have been added to mimic local pond conditions. In a split-plot design, 28 square tanks were each stocked with one hundred 15-day-old post-larvae tiger prawns (Penaeus monodon). Four tanks were used as controls and 24 were assigned to the treatments, 12 with whole and 12 with chopped leaves. Of the treatment tanks, 4 received liquid compost from vegetable, 4 received fruit, and 4 received mixed vegetable and fruit. Shrimp were weighed at the start, halfway point, and the end of the 50-day trial, and fed at 5% of the estimated total weight; survival was counted at the end. The survival rates of treatments and controls (65–76%) were not significantly different. Shrimp in water with vegetable compost grew significantly faster (2.7% day−1) than in both treatments with fruit (2.5% day−1), while all treatments were associated with significantly faster growth than were the controls (2.0% day−1). The lower growth rate of shrimp fed fruit compost may have been due to dinoflagellates, which are known to negatively affect shrimp. Shrimp in tanks with chopped mangrove leaves grew slightly better than shrimp in tanks with whole mangrove leaves.

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The high organic waste content of river water in Demak, north coast of Java, has caused traditional small-scale pond farmers to stop stocking shrimp. This paper examines whether seaweed and mussel will improve the quality of water these farmers use. The effect of Gracilaria verucosa and Perna viridis on the water quality was assessed by measuring the removal rates (RRs) of total organic material (TOM), total ammonia nitrogen (TAN), nitrite, and nitrate. The specific growth rates (SGRs) of seaweed and mussel were also measured. Thirty-six semi-outdoor tanks containing 800 L of brackish water and 7 cm substrate were randomly assigned to four replications of four densities of G. verucosa: 50 (S50), 100 (S100), 150 (S150), and 200 (S200) g m−2, and of P. viridis: 60 (M60), 90 (M90), 120 (M120), and 150 (M150) g m−2. Weekly, the TOM, TAN, nitrite, and nitrate contents were measured, seaweed and mussel weighted; RRs and SGRs were calculated at the end of the study. The effect of densities on the RRs was significant for both seaweed and mussel. P. viridis was more effective in reducing TOM (by 38%) than G. verucosa (7%); G. verucosa achieved higher RRs for TAN, nitrite, and nitrate. At S200, TOM and TAN decreased by 7.4% and 67%, respectively. At M90, TOM and TAN, decreased by 38% and 49%, respectively. However, nitrite increased significantly at S200 and M150. The SGR of seaweed was significantly lower at S200 than that at S150, S100, and S50. The best performing densities were S100 and M90.

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