Biofilter Effects Of Sargassum Fusiforme In Algae-Shrimp Multi-trophic Aquaculture System:Removal Of Inorganic Nitrogen

Shrimp is one of the largest cultured species for seafood supply in the world.Macro algae can play a role as biofilter to sustain the intensified shrimp aquaculture system.Sargassum fusiforme,a fast growing brown algae,commercially cultured in East Sea of China,has promising potentials to be used as biofilter for maintain culture water quality in shrimp-algae multi-trophic aquaculture systems.The present study was designed to investigate the capacities of Sargassum fusiforme to remove inorganic nitrogen species in culture water and other benefits to the aquaculture system of Penaeus vanname.Simulated sea water and real shrimp cultured water were used to validate the effects of Sargassum fusiforme for sheltering cultured shrimps from poisonous pollutants substantially transformed from protein rich feeds.The brown algae studied can effectively assimilate ammonia and nitrite in sea water,with removal rates ranging above 91%after 24 hour static treatments of sea water with ammonia of 2 mg/L.The specific removal rate(SRR)for Sargassum fusiforme to treat seawater containing 2 mg/L of ammonia was 21.3 mg nitrogen per 100g fresh algae and the SRR was 31.5 mg when the ammonia content was 4 mg/L.This brown seaweed grew faster with 24 hour artificial illumination and consequently increased dissolved oxygen compared to 12 hour white light radiation while did not cause significant differences in pH and salinities of shrimp culture media between the algae treatments and the controls.In the 14-day co-culture experiment of brown algae(10g/L)and grown white shrimp(5 cm in length),the total ammonia,nitrite and nitrate were 1.29 mg/L,0.47 mg/L and 6.64 mg/L respectively,which do not pose a threat to the health of the marine animal.The presence of Sargassum fusiforme promoted shrimp survival rate and weight increase by 12.8%and 36.4%respectively.The performances of the algae-Penaeus juvenile(0.5 cm in length)were even better than the adults,with 0.71 mg/L,0.007 mg/L and 2.45 mg/L of ammonia,nitrite and nitrate in culture water and 14.5%of survival increase at the end of 14-day co-culture,providing a favorite culture aquatic environment for the shrimps.Macro algae can effectively remove inorganic nitrogen and increases dissolved oxygen in sea water as a living biofilter in multi-trophic aquaculture systems.Sargassum fusiforme and Penaeus vanname can benefit each other in an algae-shrimp aquaculture system.However,the ratio of the brown algae and the white shrimp is the key parameter to the biofilter effects.Intensive shrimp culture systems require abundant quantity of algae.Studies on intensive algae culture schemes based on nitrogen budget of the whole algae-shrimp system are needed.