Integration of western king prawn (Penaeus latisulcatus Kishinouye, 1896) and green seaweed (Ulva lactuca Linnaeus, 1753) in a closed recirculating aquaculture system

Abstract

Integrating recirculating aquaculture systems with seaweeds is one of the strategies that can minimise wastes and risk of disease outbreaks. This study investigated the effect of integrating green seaweed (Ulva lactuca) with western king prawns (Penaeus latisulcatus) at varying stocking densities on the water quality, nutrient conversion rates and nutrient budget under closed recirculating culture system. The experiment was conducted using fifteen indoor tank recirculating systems and tested four different stocking ratios of prawns and seaweed with a control having prawns only. The four stocking ratios of seaweed and prawn biomass were 2, 4, 8 and 16 per tank. The mean concentrations of total ammonia nitrogen (TAN), NO3−–N and PO43−–P in the prawn and seaweed tanks were significantly lower (P < 0.05) in the integrated culture systems than in the prawn monoculture. U. lactuca was highly efficient in removing the inorganic nutrients from the culture systems with TAN removal rate of 59–81% and PO43−–P removal rate of 50–55%. Integrating seaweed with prawns did not significantly alter the specific growth rate (SGR) and survival rate of the prawns (P > 0.05). Ratio of C:P in seaweed tissues decreased with increasing seaweed stocking densities while C:N ratio showed an adverse trend. The nutrient conversion rate into total biomass (prawns plus seaweed) in the integrated systems was significantly higher at the highest seaweed stocking density (2.00 kg m− 2).Nutrient budget revealed that seaweed retained about 6.5–29.7% nitrogen and 1.6–13.5% phosphorus inputs while values for prawns were 28.0–31.9% and 13.5–14.6%, respectively. Seaweed also removed dissolved inorganic nitrogen effectively in the closed recirculating aquaculture system.