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Christopher M.A. Caipang*, Han Xuan Choo, Zemin Bai, Clara M. Lay-yag,  
 School of Applied Science
 Temasek Polytechnic, 529757 Singapore

Biofloc technology (BFT) is a recent application in intensive aquaculture systems, where metabolic wastes from fish and organic nitrogen from uneaten feed are converted to microbial protein by heterotrophic bacteria community through manipulating the carbon/nitrogen (C/N) ratio in the water.  This heterotrophic bacteria form macro-aggregates known as biofloc, which has many roles in the aquaculture system.

A series of experiments were conducted to optimize BFT for freshwater tilapia culture in Singapore using laboratory scale studies.  All experiments utilized a C:N of 16:1.  In Phase 1, two different carbon sources for BFT production, namely, wheat flour and corn flour were tested of their effects on water quality, microbial production and fish growth.  Two treatments (biofloc using wheat flour and corn flour) and control (no biofloc production) were prepared in triplicate 20L aquaria and stocked with tilapia fingerlings (average weight 2.5 g) at a density of 5 fish/aquarium.  Commercial pelleted feed at 35% crude protein level was fed to all fish.  The biofloc produced by both carbon sources have variable effects on water quality.  Growth of fish in wheat flour biofloc was comparable to the control group but not in the corn flour biofloc group.  The feed conversion ratio (FCR) in the biofloc groups was better than the control, with wheat flour biofloc group yielding the best results.  

In Phase 2, the use of sweet potato flour as a carbon source for BFT was tested.  Tilapia fingerlings (15 g body weight) were stocked in glass aquaria with biofloc (wheat flour and sweet potato flour) or without (control) and grown for 30 days.  Water quality in the sweet potato biofloc group was generally better than in the wheat flour biofloc group, but the growth of fish was lowest among all the groups.  Lowest FCR was obtained in the wheat flour biofloc group.  

Based from the results in Phase 1 and 2, the effects of wheat flour on BFT production in bigger tanks were assessed.  Duplicate tanks (200L capacity) were prepared for biofloc (wheat flour) and control (no biofloc) followed by stocking with 35 tilapia fingerlings (4.75 g) and reared for 55 days.  Variable water quality was observed in both groups.  The growth of fish was comparable in both groups but the FCR in the biofloc group was better than the control.  Higher total bacterial counts and Bacilli population were obtained in the biofloc groups than the control in all the three experiments.   

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