Water quality trials in four recirculating aquacultural system configurations

Four circular, 2000-1, fiberglass tanks in four independent, indoor recirculating aquacultural systems were stocked with hybrid striped bass fingerlings (60-g average weight) at similar densities (320 fish/tank at the start of the study). The four systems represented four different recirculating system configurations as obtained by the combination of two types of biofilters (trickling and bead) and two types of solids removal filters (rotating screen filter and multi-tube settling basin). Fish were fed a commercial fish feed during experimental trials at two different feeding rates, 600 (two trials) and 800 (two trials) g/system per day. Water quality characteristics were observed on a regular basis in all the four trials. This paper presents statistical comparison of water quality characteristics including total organic carbon (TOC) concentration and biochemical oxygen demand (BOD) of the four systems. Effects of biofilter, particulate filter, feeding rate, and interactions among them on water quality characteristics and system water exchange rate are discussed. The systems with trickling biofilters had lower concentrations of total ammonia nitrogen (TAN), nitrite-nitrogen (NO2-N), and TOC in the tank water when compared to those of the systems with bead biofilters. The systems with a screen type particulate filter required lower amounts of make-up water as compared to the systems with settling basins. (C) 1999 Elsevier Science B.V. All rights reserved.