“Growth, digestive activity, welfare, and partial cost-effectiveness of genetically improved farmed tilapia (Oreochromis niloticus) cultured in a recirculating aquaculture system and an indoor biofloc system” (Luo et al 2014)

Citation: Luo, G., Gao, Q., Wang, C., Liu, W., Sun, D., Li, L., and Tan, H. (2014). “Growth, digestive activity, welfare, and partial cost-effectiveness of genetically improved farmed tilapia (Oreochromis niloticus) cultured in a recirculating aquaculture system and an indoor biofloc system.” Aquaculture, 422-423, pp. 1-7. DOI: 10.1016/j.aquaculture.2013.11.023

Summary by: Alexandra Pounds

Image Credit: Flickr

  • Big Picture: Tilapia in the biofloc system grew bigger and had a lower FCR than tilapia in traditional RAS. Further, biofloc systems was more cost-effective than the RAS.
  • This experiment compared a biofloc system (BFT) with a traditional recirculating aquaculture system (RAS) to find out which was more profitable.
  • Both BFT and RAS recycle water so that farming can take place on land. RAS typically discharges waste, whereas BFT tries to reuse the waste to feed biofloc in the system. This reduces waste, but requires more aeration to keep the biofloc suspended and oxygen levels high. It also works better with hardy filter feeders like shrimp and tilapia, because biofloc can be hard on gills due to the higher suspended solids in the water. This bacteria can help remove nitrogen from the system.
  • Methods:
    • Disolved oxygen, pH, temperature, and water levels were kept constant and equal within both systems.
    • GIFT tilapia was used in both tanks at 8.06 kg/m3 stocking density. They were all fed the same commercial pellets at 2% of biomass daily. Fish were fed 3x per day.
    • Sodium acetate was added to the BFT system at 75% of feed to maintain required Carbon to nitrogen ratio for bacterial health. Biofloc was also removed regularly, as fish did not eat enough of it to maintain the system.
    • The systems were run for 87 days.
  • Physical Results:
    • Both systems removed nitrogen waste sufficently.
    • The BFT system allowed for more efficient uptake of nitrogen and phosphorous, because the N & P in the biofloc is fed back into the fish when they eat the biofloc, instead of being removed from the system as waste.
    • No fish died in either system, and welfare parameters were no different between the systems.
    • There was no difference in lipid or protein content of the fish upon harvest; however, the biofloc system did not meet lipid requirements of tilapia.
    • Individual BFT fish were 22% heavier on average than individual RAS fish.
    • The FCR of BFT fish (1.2) was 18% better than the FCR of the RAS fish (1.47).
    • BFT fish had greater levels of metalloenzymes SODs, which shows that the BFT fish had stronger immue systems.
  • Cost comparison:
    • Energy & depreciation cost was greater for RAS because the RAS needed additional equipment to remove waste.
    • Carbon sources and aeration added to the BFT were the biggest cost in that system.
    • BFT was more cost effective than RAS.
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