Effect of fish size and hydraulic regime on particulate organic matter dynamics in a recirculating aquaculture system: elemental carbon and nitrogen approach

Abstract Understanding the capabilities of particulate organic matterremoval devices is critical to the development of recirculating aquaculture systems(RAS). The size of fish and water flow rates were evaluated as factors determining the distribution of particulatewastes throughout the RAS. Elemental carbon and nitrogen analyses (CHN) were employed in order to characterize particulatematter and to evaluate the performances of solid evacuation devices during the rearing of two sizes of European seabass ( Dicentrarchuslabrax) at four water flow rates. Carbon mass balances show that the rearing tank stocks/transforms (out of fish growth and respiration) 33–16% of the particulatecarbon from ingested feed when small (60–100 g) and big (500–600 g) fish, respectively, are reared. On the other hand, the treatment loop consumes 32% and 14% of particulatecarbon that arrives from the same group of sizes. Water flow rates through rearing tanks affect solids evacuation, increasing retention of particles and modifying water quality through a decrease in the hydraulic regimes. Concerning treatment loop of the RAS in this study (2 m 3 ), a minimal hydraulic loading rate (36.94±3.19 cm min −1 ) is necessary in order to avoid the biofilterclogging by retention of particulatematter, and also to allow a sufficient hydraulic retention time(6.5 min in biofilterand 18.5 in all treatment loop) to enhance a proper nitrification rate and a minimal particulatecarbon consumption. Dynamics between dissolved and particle materials depend on the fish reared and the management of treatment devices that comprise the RAS.