Integrated multitrophic aquaculture in Maninjau Lake: converting eutrophic water into fish meal

Abstract

Maninjau lake has currently been under eutrophic condition and needs urgent efforts to recover it. Integrated multitrophic aquaculture (IMTA) has proposed as one among those pointed measures, by using lake water to perform inland aquaculture activity, in which an aquatic plant was employed to carry out double functions, as water phytoremediator and source of natural feed for fish. This research was focused on the ability of the duckweeds to support growth of Tilapia (Oreochromis niloticus), carried out in IMTA ponds located at Nagari Batang, Maninjau Lake, West Sumatra for 40 days (September-October 2018). IMTA systems have been implemented as an effort to utilize lake water for growth media. It consisted of 3 tilapia ponds of 4×6 m2 and 12 duckweed ponds (8 ponds of 4×4 m2 and 4 ponds of 4×8 m2). The lake water was lifted up into the fish ponds (265 fishes/pond) and then channeled down into the duckweeds ponds, so as the duckweeds grew while absorbing nutrients content of waste fertile water from the fish ponds. The obtained duckweed biomass was then fed up to the fish. The result showed that the fish average SGR was 0.54 (0.31-0.73)%, the survival rate was 95.26 (92.88-98.12)% and the average FCR was 21.03 (14.02-28.29). Proximatee analysis of the fish showed the protein content was 45.767 (42.17-50.99)% and lipid was 7.923 (4.42-11.79)%. The daily production of duckweed was 48.19 (35.00-72.92) g/m2/day; with SGR 17.57 (3.15-31.43) %, while the protein content of Lemna was 32.896 (29.58-36.22)% and lipid 9.732 (8.47-10.99)%. The duckweed was able to convert eutrophic water into useful biomass for fish feed and can be promoted to support development of inland aquaculture activity nearby the Maninjau Lake.