The effects of decomposing mangrove leaf litter tannins on the water quality, growth and survival of tiger prawn (Penaeus monodon) post-larvae

Integrated mangrove-shrimp sylvo-aquaculture is an ecosystem-based system practiced in Purworejo, Demak, Indonesia. Mangrove leaves may impact shrimp health and yield. Therefore we compared the effect of decomposing fresh leaves of Avicennia marina and Rhizophora apiculata, on water quality and performance of tiger prawn (Penaeus monodon) post-larvae (PL). Hundred PL21 (0.28g) were stocked in 33 aerated tanks, with 800L of brackish water, assigned to triplicates of six concentrations (g/L) of both species’ leaves: 0 (control), 0.125, 0.25, 0.5, 0.125 minced leaves and 0.125 leachate of minced leaves. The PL were fed 3x daily with pellets at 10% of initial total body weight. Temperature, salinity, dissolved oxygen (DO) and pH were recorded daily. Tannin, H2S and NH3-N concentrations were measured every ten days. After 37 days, growth and survival were measured. Treatments and leaf’ concentrations had no effect on DO, tannin, NH3-N and H2S, but pH was slightly reduced to 8.4 (P<0.05). NH3-N increased from 0.67 mg/L to levels critical and lethal to the PL (> 0.74 to 0.99 mg/L). Mean tannin concentrations were low (marina: 1.9 ± 1.4; apiculata: 2.1 ± 1.5 mg/L) and did not correlate with other water quality parameters, nor survival rate (62 ± 14 to 70 ± 8) and shrimp growth (1.5 to 2.1 g). The higher weight in 0.5 g/L apiculata was probably related to a higher mortality rate and thus feed availability. The NH3-N levels with decomposing mangrove leaves of Avicennia marina and Rhizophora apiculata were toxic for shrimp in tanks without water exchange.