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.

膳食磷 (P) 水平影响鱼中正磷酸盐 (PO ₄ -P)的排泄。由于大多数循环水产养殖系统 (RAS) 不会专门去除再循环回路中的PO ₄ -P，因此膳食 P 水平可能会影响RAS 水中的PO _{4 -P 浓度。}在淡水 RAS 中进行了一项饲喂试验，旨在确定日粮 P 水平与RAS 水中PO ₄ -P 积累之间的关系，并检查日粮 P 水平对微生物活性和 RAS 水中丰度的潜在影响，因为 P 是一种所有微生物必需的矿物质。将总磷含量分别为 1.49% (HiP)、1.20% (MeP) 和 0.89% (LoP) 的三种饲料分别喂给虹鳟鱼幼鱼，以进行三次中试规模的 RAS 试验。Oncorhynchus mykiss )持续五周，每日饲料负荷为1.67 kg饲料/m ³补充水。试验结束时，可消化膳食磷水平与 RAS 水中的 PO _{4 -P 浓度显着相关，但与微生物丰度或活性没有观察到类似的相关性。}试验结束时测得的硝酸盐-N 浓度与预测的平衡浓度相匹配。相比之下，无论饮食如何，测得的 PO ₄ -P 浓度均比预测值低约 40 – 50%，这表明 PO ₄ -P 可能被 RAS 微生物利用。因此，我们推测降低膳食磷水平是否可以成为 RAS 微生物管理的有效工具。