I. Nutritional Value and Functions of the Two Supplements

1. Cabbage
   • Dietary Fiber: Promotes intestinal motility, preventing winter constipation (common due to slowed digestion in low temperatures).
   • Vitamin Supplementation: Rich in vitamin C, K, and folate, enhancing immunity and stress resistance.
   • Moisture Regulation: High water content (≈95%) helps maintain fluid balance.
2. Tofu
   • Plant-Based Protein: Provides easily digestible protein, compensating for reduced animal protein intake in cold periods.
   • Minerals and Isoflavones: Calcium supports scale health, while soy isoflavones offer mild antioxidant benefits.
     

II. Prerequisites and Water Temperature Requirements

1. Applicable Water Temperature Range: Only feed when water temperature ≥10°C (e.g., in greenhouse ponds or mild southern winters).
2. Contraindicated Temperatures: When water temperature <10°C, stop all feeding, including supplements. At this point, koi metabolism is nearly halted, and feeding can cause food stagnation, decay, and poisoning in the intestines.

III. Scientific Feeding Methods

1. Cabbage Preparation
   • Choose organic, pesticide-free cabbage, using the outer older leaves (higher in fiber).
   • Blanch for 30 seconds to soften fibers, then chop into 1 cm × 1 cm pieces.
   • Feed 1–2 times weekly, with each feeding not exceeding 0.5% of the koi’s body weight.
2. Tofu Preparation
   • Use plain, unseasoned soft tofu (avoid fried or seasoned varieties).
   • Boil for 3 minutes to remove anti-nutritional factors (e.g., trypsin inhibitors), cool, then crumble.
   • Feed once every two weeks, alternating with cabbage, at 0.3%–0.5% of body weight.
3. Feeding Timing
   • Choose warmer afternoon periods (e.g., 13:00–15:00), avoiding early morning or nighttime when temperatures are lower.
   • Pause main feed before offering supplements, and remove uneaten residue within 1 hour of feeding.
     

IV. Precautions and Risk Control

1. Water Quality Protection
   • Tofu crumbs disperse easily; place a fine mesh screen at the filter inlet.
   • Remove leftover cabbage stems promptly to prevent decomposition and nitrite production.
2. Suitability Based on Physique
   • Older koi (>8 years) or those with weaker digestion should only be offered blanched cabbage, avoiding tofu.
   • Koi with enteritis or bloating should not receive supplements until fully recovered.
3. Regional Adjustments
   • In northern heated indoor ponds (water temperature ≥15°C), regular weekly supplementation is feasible.
   • In southern natural ponds, adjust flexibly based on real-time water temperatures.
     

V. Alternative Options and Nutritional Complementation

• Specialized Low-Temperature Feeds: Wheat germ-based feed (protein ≤28%), fermented feed.
• Natural Alternatives: Cooked pumpkin (rich in beta-carotene), unsalted seaweed sheets (mineral supplementation).
  
  
  
  Conclusion
  Cabbage and tofu act as "gentle supplements" to winter koi nutrition but must adhere to the principles of "water temperature as the guideline, moderation as the rule." They can diversify the diet but should not replace the core nutrition provided by professional feeds. True winter care for koi lies in offering every meal that is "safe to eat and comfortably digestible."