<p>Phosphorus is an essential nutrient for fish. Given that phosphorus concentrations in aquatic environments are typically minimal, fish depend primarily on dietary sources to fulfill their phosphorus requirements. However, when dietary phosphorus intake exceeds the biological needs of fish, the surplus is excreted into the environment, leading to ecological degradation. To address this, dietary phosphorus levels are often maintained slightly below the estimated requirements, with periodic evaluations of fish phosphorus status. This is essential because chronic phosphorus deficiency can hinder fish growth without obvious external signs, leading to inefficiencies in aquaculture production. Conversely, when the fish phosphorus status is near saturation, it likely indicates an excess dietary phosphorus intake rather than an exact match to its requirements. In this case, reducing dietary phosphorus levels will be required to protect surrounding water bodies. This paper explores the most practical and useful in situ diagnostic indicators for assessing fish phosphorus status, including bone ash, scale ash, body calcium content, and rib deformities, along with extensive reference data and clinical figures across various fish species.</p>