Abstract
Ecosystem responsible aquaculture practices are today imperative to feed the world increasing population. Theculture of extractive species such as oyster with fed species such as fish is a promising solution to recycle wastestreams, which would be otherwise lost and discharged into the surrounding environment. In Mediterraneanearthen ponds, meagre (Argyrosomus regius), white seabream (Diplodus sargus) and grey mullet (Mugil cephalus)are three fish species of different trophic levels that are good candidates to be raised in integrated multi-trophicaquaculture (IMTA) pond with oysters (Magallana gigas) and macroalgae (Ulva flexuosa). Trophic links betweenspecies raised in IMTA ponds were inferred using the analysis of body fatty acid composition as well as in carbonand nitrogen stable isotopes. A combination of 3 treatments was tested: fish, oysters, phytoplankton and mac-roalgae (T1); fish, oysters and phytoplankton (T2); fish, phytoplankton and macroalgae (T3). Our results high-lighted that the three fish species were in competition for food sources as they mainly fed on commercial feedwhatever the treatment. However, grey mullet also consumed polychaetes that naturally grown in ponds.Macroalgae were not used by fish. In T1 and T2, oysters actively consumed the excess of phytoplankton. In T2,the absence of macroalgae reduce nutrient competition for phytoplankton growth and oysters have moreavailable food. In earthen ponds, the production of fish with macroalgae or fish with oyster should be privilegedcompared to usual semi-intensive fish polyculture as the presence of extractive species reduced fish wastes.