Biofilm cultivation with three stuffings and their effect on the growth of young black sea bream, Sparus macrocephalus

Abstract

Within recirculating aquaculture systems(RAS),the bio-filter plays a critical role by removing dis-solved inorganic nitrogen,intercepting suspended matter,and constantly recycling the culture water.The nitrify-ing performance of the bio-filter is heavily influenced by bio-fillers and as such the optimal method for removal of deleterious substances remains a focus of research.Microbial water purified agents are often used as a water amendment in artificial culture systems.Their use is thought to promote water purification and disease prevention in fishes,though few studies have evaluated the use of microbial water purified agents as strains for bio-film cul-tivation.RAS allows high culture density and rapid growth of cultured species,though compared with the tradi-tional flowing water culture,little is known about the effect of fish culture in RAS.We evaluated bio-film cultiva-tion and the dissolved inorganic nitrogen removing efficiency of three kinds of bio-fillers.In addition,we deter-mined their effect on the growth of young black sea bream,Sparus macrocephalus.We tested the effect of using microbial water purified agents as a strain for three different kinds of fillers(pottery ring,elastic brush,and bio-chemical cotton fiber) during biofilm cultivation.The bio-film maturation time for the three fillers was 25,32,and 28 d,respectively.Our results suggested that maintaining high dissolved oxygen concentrations,changing the water,and adding nutrients and NaCO3 promoted the growth and propagation of nitrifying bacteria.Conversely,NO2-N concentrations cannot be held at high levels for an extended period because ammonia-oxidizing bacteria and nitrifying bacteria require dissolved oxygen and alkalinity for survival.Young black sea bream grew well in the simple recirculating aquaculture system.After 40 d feeding,the mean body weight and feed conversion rate of black sea bream in the three experimental groups differed significantly from that in the control group(P0.05).The survival rates in all groups were 95%.The activity of serum LSZ and liver SOD was significantly higher in the experimental groups than the control group(P0.05).Similarly,the quantity and diversity of digestive tract flora was significantly higher in the experimental groups than the control group.We identified several different kinds of beneficial bacteria in the three experimental groups,relative to the control.Our results suggest that these benefi-cial bacteria are dominant,and thus inhibited the survival of pathogenic bacteria.During circulation of the water,the beneficial bacteria are able to enter the fish body during respiration and ingestion,thereby enhancing the non-specific immunity of the fish.Our results suggest that different filter materials have different bio-film maturation times under the same operating conditions.A recirculating aquaculture system can not only improve fish growth,but also enhance their immune performance.