In response to the current market preference for a "plump body shape," the protein content in koi feed is recommended to be maintained within the range of 42%–46%, with fine adjustments based on growth stages:
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Tosai (≤1 year old): Peak protein requirement period, recommended 45%–48% to support rapid skeletal framework development.
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Sub-adults (2–3 years old): Body-filling stage, suitable range 43%–46%, focusing on muscle and back development.
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Adults (≥4 years old): Body maintenance stage, can be reduced to 40%–42% to avoid excessive strain on internal organs.
It must be emphasized that protein content is not an isolated indicator and must be considered in synergy with the following factors:
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Protein Source Formulation: Animal-based proteins (fishmeal, krill meal) should account for >60% to ensure completeness of essential amino acids.
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Energy-to-Protein Ratio: An appropriate ratio is approximately 35–40 kcal per gram of protein to prevent protein from being converted into energy.
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Dynamic Stage-Specific Adjustments: Increase protein to 44% before the breeding season and reduce it to below 38% during overwintering.
Notably, blindly pursuing ultra-high protein (>50%) may exacerbate liver-pancreas burden and cause spikes in water ammonia levels. Scientific protein management should always prioritize "lifelong health of koi", seeking a balance between body shaping and metabolic safety.
