Origine, devenir et contrôle de la matière particulaire dans les élevages de poissons marins en système recyclé

The particulate matter plays an essential role in the functioning of recirculating aquaculture systems (RAS). Rich in organic substances, it provides ideal conditions for the bacterial development, which contribute to its mineralization. The understanding of interactions between the bio-geochemical cycles of carbon and nitrogen in these processes is necessary to define an effective and adapted management of aquaculture facilities. A methodology using natural stable isotopes (13C and 15N) and elemental carbon and nitrogen analysis on particulate matter, allows to identify its sources and to quantify its fluxes. Applying this methodology, we found an enrichment of 13C in dorsal muscle of reared fish and non differences of 13C in fish liver compared to the feed. The 13C in particulate matter was preserved by recycling and by mechanical fractionation throughout the RAS. On the other hand, 15N shifts shown the biochemical transformations on particulate matter in the RAS. Particulate matter constitutes a complex mixture of detrital (feed traces and feces) and living materials (bacterial aggregates). The isotopic shifts indicate that contributions of the three sources depends on: 1) fish metabolism, 2) water treatment devices and 3) bacterial activity. These factors and the water flow rate, determine the distribution of particulate matter in the recirculating system. Feed additives to increase the quantity of evacuated feces and diatomaceous earth filtration significantly diminished the availability of particulate carbon, but did not appreciably affect the biofilter performance. A model, which describe the production and elimination of particulate matter was built considering its transformations through the recirculating system and the efficiency of the evacuation devices. After its calibration and validation, this model will be a tool for evaluation and prediction of particulate matter dynamics in recirculating aquaculture systems.