Low-technology recirculating aquaculture system integrating milkfish Chanos chanos, sea cucumber Holothuria scabra and sea purslane Sesuvium portulacastrum

Abstract

Closed recirculation aquaculture systems (RAS) in combination with integrated multi-trophic aquaculture (IMTA) are considered best management practices, but high material costs and difficult maintenance still hinder their implementation, especially in developing countries and the tropics. Few case studies of such systems with tropical species exist. For the first time, an extremely low-budget system was tested combining the halophyte sea purslane Sesuvium portulacastrum and a detritivore, sandfish Holothuria scabra, with finfish milkfish Chanos chanos over 8 wk on Zanzibar, Tanzania. In a 2 m3 RAS, milkfish and sea purslane showed good growth, producing an average (±SD) of 1147 ± 79 g fish and 1261 ± 95 g plant biomass, while sea cucumber growth was variable at 92 ± 68 g. The system operated without filter units and did not discharge any solid or dissolved waste. Water quality remained tolerable and ammonia levels were reliably decreased to <1 mg l-1. A NO2- peak occurred within the first 30 d, indicating good biofilter performance of the different system compartments. Changes in dissolved inorganic nitrogen (DIN) species support the notion that the sea cucumber tank was the main site of nitrification, while the hydroponic halophyte tank acted as a net sink of NO3-. A nitrogen budget accounted for 63.7 ± 5.3% of the nitrogen added to the system as fish feed. Increasing the plant to fish biomass ratio to 5:1 would fully treat the DIN load. The experiment provides proof-of-concept of a simple pilot-scale RAS, integrating tropical species at 3 trophic levels.

Effect of feeding rate on growth and feed conversion ratio in the cultivation recirculation systems of multi tropic model

“…The IMTA model with a recirculation system, as in this study, can create better water quality because the remaining feed, feces, and excretions are recirculated to the green mussels, sea urchin, and seaweed rearing containers and utilize them for growth. The cultivation of the IMTA model of the recirculating system can maintain good water quality and reduce the accumulation of solid waste because it is utilized by other organisms [30][31][32].…”

Exploring the potentials of Sesuvium portulacastrum L. for edibility and bioremediation of saline soils

“…S. portulacastrum grown in floating beds can significantly reduce dissolved inorganic N and P to meet water quality standards ( Liu et al., 2019 ). Sea purslane plants grown in floating beds not only absorb N and P but also provide fish with food ( Senff et al., 2020 ).…”

Toward integration of sea cucumber and cockles with culture of shrimps in earthen ponds in Kenya

“…Wild stock depletion and increased demand for the species triggered interest to develop culture techniques for H. scabra aimed at increasing the numbers, reducing fishing pressure from the wild while providing alternative sources of income in different countries across the globe (Kumara & Dissanayake, 2017). Some countries like Vietnam, Madagascar, Tanzania, and the Philippines initiated restocking and sea ranching (Eriksson, de la Torre‐Castro, Purcell, & Olsson, 2014; Kunzmann, Beltran‐Gutierrez, Fabiani, Namukose, & Msuya, 2018; Purcell, Hair, & Mills, 2012; Senff, Blanc, Slater, & Kunzmann, 2020; Watanabe, Sumbing, & Lebata‐Ramos, 2014).…”