Development of a low-cost polyculture system utilizing Hygroryza aristata floating grass in the coastal wetlands of Bangladesh

Worldwide the quality and high price of fish feed are an important issue for sustainable aquaculture that warranted the development of low-cost culture systems utilizing natural resources. An experiment was conducted in a tidally inundated wetland in the coastal region of Bangladesh utilizing naturally grown floating grass, Hygroryza aristata as a fish feed. The experiment was conducted under three treatments each with three replications for one year. In treatment one, the grass was planted and grown on the bottom soil before stocking of fish (T1; in-situ grass); in treatment two, the grass grown elsewhere was collected and supplied as fish feed in raw condition (T2; ex-situ grass); and in treatment three, the fishes were fed with commercial floating fish feed (T3; control). Grass carp, common carp, black carp and tilapia were reared at the ratio of 6:1:1:2 with a total stocking density of 12,350 fish ha−1. The survival rate, growth (weight gain, % weight gain and specific growth rate, SGR), production and cost and benefit of fish production were calculated. The survival of the fish varied from 76.00% to 85.14% irrespective of species. The weight gain, % weight gain and SGR of grass carp and common carp were highest in in-situ grass, followed by ex-situ grass and control, whereas tilapia showed the highest growth in control, followed by in-situ and ex-situ grass. The total production of fish was highest in in-situ grass (9060.70 kg ha−1 year−1), followed by control (8469.70 kg ha−1 year−1) and ex-situ grass (8001.23 kg ha−1 year−1). The net economic benefit and benefit-cost ratio were also highest in in-situ grass (US$ 17,994.96 ha−1 and 4.52), followed by ex-situ grass (US$ 14,278.30 ha−1 and 2.78) and control (US$ 4818.63 ha−1 and 0.32). The present findings indicate that coastal wetlands of Bangladesh can be used for commercial aquaculture using the H. aristata floating grass as fish feed, which may play an important role in the livelihood development of the people living in the coastal areas of the country. © 2020 Elsevier B.V.