Application of Integrated Multi-trophic Aquaculture (IMTA) Concept in Brackishwater Eco-system: the First Exploratory Trial in the Sundarban, India

Abstract

An integrated multi-trophic aquaculture (IMTA) model involving mullets (Mugil cephalus and Liza parsia) and tiger shrimp (Penaeus monodon) as fed-species, and estuarine oyster (Crassostrea cuttackensis) and seaweed, Enteromorpha spp. as extractive species was evaluated as a viable aquaculture option in brackishwater of the Indian Sundarban. A 150-day field experiment was conducted in six brackishwater ponds (600 m2 each). There were two randomly assigned groups, IMTA and polyculture (control) with three replicate ponds. Ponds under IMTA were stocked with mullets and tiger shrimp at 10000 and 30000 no./ha, respectively, C. cuttackensis at 1600 no./ha suspended with a basket in the water column and Enteromorpha spp. at 200 kg biomass/ha. Control ponds were stocked with mullets and shrimp at the same densities to that of IMTA, and devoid of oyster and seaweed. A common low-cost polyculture feed was provided to fishes and shrimp. Mullets attained a significantly higher growth (p <0.05) in the IMTA system compared to that of control ponds, whereas tiger shrimp had insignificantly higher growth in IMTA than in control. Significantly higher production of 1707 kg/ha (19% higher) with better water quality was obtained in IMTA system compared to that of control ponds (1434 kg/ha) (p <0.05). There was a significant reduction in apparent feed conversion ratio by 22%, and an increase in net income by 69% and benefit-cost ratio by 30% in the IMTA system than that of the control. Moreover, for the first time the estuarine oyster, C. cuttackensis was used as an extractive species in brackishwater IMTA system. From an indoor trial, it was observed that this oyster species has high water filtration capacity to remove suspended matters, including planktons. This preliminary experiment indicates the application of IMTA concept in brackishwater as a viable environment-friendly option and warrants further refinement for species combination with the economic viability and environmental suitability.