Populations of heterotrophic bacteria in an experimental recirculating aquaculture system

The aim of this work was to identify the main viable heterotrophic bacteria in a marine fish farm with a recirculating water system and to study their growth dynamics. The experiments were performed with sea bass (Dicentrarchus labrax) in an experimental recirculating water system. The bacteria identified were typical of the marine environment: Pseudomonas, Oceanospirillum, Marinobacter, Paracoccus and Erythrobacter genus from Bergey’s group IV, two genus of Vibrionaceae, one strain of Vibrio and one strain of Aeromonas. These populations were stable when the ingested feed/replacement water ratio was kept constant. Fixed bacteria formed large biofilms, which released about 104 CFU ml−1 into the tank. The biological filter, with its large surface area, was the largest source of bacteria in the farm, but the UV disinfection unit kept the number of free bacteria stable. When properly managed, the majority of bacteria that grew on the biological filter were from Bergey’s group IV; no Vibrio were ever detected on it.