Coupling of dietary phosphorus and growth across diverse fish taxa: a meta-analysis of experimental aquaculture studies

Imbalances in phosphorus (P) intake relative to demand negatively affect animal growth, but their consequences are less understood for vertebrates, in which bone represents a significant and potentially flexible pool of P. Flexibility in body-P content could buffer vertebrates from the effects of imbalances between P intake and demand, reducing the likelihood of a sharp stoichiometric knife-edge in the relationship between growth rate and diet-P level. We conducted a meta-analysis of published aquaculture experiments that tested effects of diet %P on fish growth rate (49 studies, 28 species) and body-P content (27 of the studies in the main data set, 20 species). Our meta-analysis revealed significant P limitation of growth, as well as significant negative effects of excess P on growth rate. Diet-P thresholds for these effects occurred at ecologically relevant levels (optimal diet-P of 1.2% +/- 0.45%, mean +/- SD, under experimental conditions of high ration). Finally, the analysis also suggested a pattern of relatively shallow relationships between growth rate and diet-P level, coupled with surprisingly flexible body-P content in fishes. This result is consistent with fish using flexible body-P content (presumably mediated through bone P) to buffer imbalances between P intake and demand. Together, our results provide evidence for a relatively dull stoichiometric knife-edge in fishes, driven in part by flexible body-P content.