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Trophic functioning of integrated rice agriculture to fish aquaculture in Madagascar: Insights from stable isotopes (d13C & d15N)

Mortillaro J.M., Andria Mananjara D.E., Randriamihanta T.H., Andriamaniraka H., Martel P., Andriamarolaza R., Raliniaina M., Mikolasek O., Aubin J.. 2019. Bogor : IRD; Indonesian national Research Institute for Freshwater Aquaculture and Fisheries Extension (RIFAFE), 1 p.. Ecological intensification: A new paragon for sustainable aquaculture Conference, 2019-10-28/2019-10-30, Bogor (Indonésie).

Flooded rice fields are ecosystems favorable to growth and production of aquatic organisms. They can even play a major role in feeding and nutrition of local communities, as source of self-recruiting species or supporting production of farmed fish in association with rice. In Madagascar, integrated rice-fish culture has proven a yield net increase, without fertilizers or feed inputs, of more than 10% compared to traditional rice culture. Common carp (Cyprinus carpio), have been either demonstrated to improve rice production through fertilization of rice plots. Fertilization is indeed provided through bioturbation of sediments aside from any confirmed impact on pests and weeds. Although common carp can improve rice production, fish is often limited to small yields (av. 50kg/ha/cycle). Fish yields can however reach 500kg/ha/cycle (av. 100 days) through intensification with fertilizers and feeds. In that context, trophic characterization of rice-fish systems may improve knowledge on ecosystem functioning as well as fish and rice yields. Natural abundances of carbon and nitrogen stables isotopes ratio (d13C and d15N) are often used in ecological studies to characterize trophic functioning of aquatic ecosystems. The aim of the current study was therefore, to characterize feeding behavior of common carp in rice fish integrated agriculture to aquaculture system, through stable isotopes analysis of the compartments of this aquatic ecosystem. At the beginning of the experiment, carp larvae signature was -18.8±0.5‰ and 9.3±0.6‰, for d13C and d15N respectively. This signature suggest that larvae feeds were supplied by animal proteins (e.g. fish meal) and C4 carbohydrate (e.g. corn). However, following 100 days of extensive feeding in the riceplot, fish signature was depleted compared to larvae, down to -24.9±1.0 and 5.7±0.9‰, for d13C and d15N respectively. Stable isotopes signatures of produced fish were in the range of riceplot ecosystem, confirming that feeding was supplied

Mots-clés : aquaculture; isotope; riz aquatique; rizière; niveau trophique; rizipisciculture; madagascar

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