Influence of dietary phosphorus on orthophosphate accumulation in recirculating aquaculture systems with rainbow trout (Oncorhynchus mykiss)

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Abstract

Dietary phosphorus (P) levels affect the excretion of orthophosphate (PO4-P) from fish. Since most recirculating aquaculture systems (RAS) do not specifically remove PO4-P within the recirculating loop, dietary P levels may influence PO4-P concentrations in RAS water. A feeding trial was performed in freshwater RAS, aiming to determine the relationship between dietary P levels and PO4-P accumulation in RAS water, and to examine potential effects of dietary P levels on microbial activity and abundance in RAS water given that P is an essential mineral for all microorganisms. Three diets with 1.49% (HiP), 1.20% (MeP), and 0.89% (LoP) total P, respectively, were each fed to triplicate pilot-scale RAS with juvenile rainbow trout (Oncorhynchus mykiss) for five weeks, applying a daily feed loading of 1.67 kg feed/m3 make-up water. Digestible dietary P levels correlated significantly with the PO4-P concentrations in RAS water at the end of the trial, while no similar correlations with microbial abundance or activity were observed. Nitrate-N concentrations measured by the end of the trial matched predicted equilibrium concentrations. In contrast, measured PO4-P concentrations were approximately 40 – 50% lower than predicted regardless of diets, suggesting that PO4-P was likely utilized by RAS microbes. We therefore speculate whether lowering dietary P levels could become an effective tool for microbial management in RAS.
Original languageEnglish
Article number102363
JournalAquacultural Engineering
Volume103
Number of pages6
ISSN0144-8609
DOIs
Publication statusPublished - 2023

Keywords

  • Microbial water quality
  • Nitrate-N concentrations in RAS
  • Ortho-P concentrations in RAS
  • RAS water management
  • Rainbow trout

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