Conceptualization of plankton ecology – aquatic animal nutrition (PEG-Nutrition) model for temperate shallow-lake ecosystems: synthesis from experimental fishponds as living labs

Drawing on a whole-ecosystem study of carp-managed ponds, we demonstrate that high primary productivity and elemental nutrient supply (C, N, P) can coexist with severe deficits in essential biomolecules—particularly amino acids and lipids—leading to a breakdown in trophic transfer efficiency. This biochemical mismatch, masked by conventional ecological models, limits fish growth and contributes to nutrient accumulation and water quality degradation. The PEG-Nutrition model reveals a seasonal shift from a nutritionally supportive “clear-water” phase to a late-season state of “nutritional dysbiosis,” where ecosystem productivity no longer supports consumer biomass. The model offers a new mechanistic understanding of shallow-lake metabolism.