Phosphorus (P) is an indispensable nutrient for fish but when present in diets in unavailable form or in excess, it is excreted to receiving waters. In the aquatic environment, P has been widely recognized as a key driver of eutrophication, which can decrease biodiversity, alter ecosystem dynamics, and result in dead zones.
The objective of this trial was to assess if excess dietary P would be excreted by the fish and detected in the water. To this end, 40 juvenile Koi (Cyprinus rubrofuscus) at the Kentucky State University Aquatic Animal Nutrition Lab were fed two different diets: a balanced diet (Diet 1) and a diet with excess P (Diet 2). The Koi were stocked at five fish per tank (110 L) with four replicates per treatment and were fed to satiation once daily. The evaluation was conducted over a 12-h period and P levels were measured every four hours. The results showed that there was a significantly higher concentration of P in the water of tanks assigned Diet 2 (Figure), indicating that the fish did not retain the excess P.