I. Effects of High Temperatures on Koi Physiology

1. Increased Metabolism but Reduced Digestive Efficiency
   At water temperatures above 30°C, koi metabolism accelerates, but digestive enzyme activity is suppressed by the heat. This shortens food retention time in the intestines and reduces nutrient absorption efficiency.
2. Contradiction Between Oxygen Demand and Supply
   High temperatures lower the dissolved oxygen saturation in water, while koi metabolic oxygen consumption increases. Feeding further exacerbates the risk of hypoxia during digestion.
3. Fluctuating Immunity
   Prolonged high temperatures can place koi in a suboptimal health state, weakening the intestinal mucosal barrier and increasing susceptibility to pathogens.

II. Core Principles for Feeding in Summer Heat

1. Reduce Quantity and Frequency, Prioritize Quality Over Quantity
   • Decrease feeding amounts to 50%–70% of peak season levels (23–28°C), adjusting based on water temperature:
     • 30–32°C: Feed 60%–70% of normal amount
     • 33–35°C: Feed 50%–60% of normal amount
     • Above 35°C: Suspend feeding or offer only symbolic amounts (<1% of body weight)
   • Feed 2–3 times daily, avoiding excessive amounts per feeding.
2. Stagger Feeding Times, Choose Optimal Periods
   • Best times: Early morning (5:00–7:00, when water temperature is lowest) and evening (19:00–20:00, after sunset when temperatures drop)
   • Extended option: On cooler nights (21:00–22:00), supplement with small amounts of easily digestible feed
   • Strictly avoid: Midday (11:00–15:00) when sunlight is strongest and water temperatures peak
3. Optimize Feed Composition
   • Increase the proportion of easily digestible protein (e.g., fish meal, shrimp meal) and reduce plant protein content
   • Add vitamin C (200–500 mg per kg of feed) and probiotics (e.g., Bacillus subtilis) to enhance stress resistance
   • Supplement moderately with vegetable/fruit treats (e.g., watermelon rind, chopped spinach) to help cool the body
     

III. Coordinated Water Quality and Equipment Management

1. Enhance Aeration
   • Run aeration equipment continuously to ensure dissolved oxygen >6 mg/L; turn on additional air stones for 1 hour after feeding
   • Use circulation/wave pumps to increase water flow and prevent localized hypoxia
2. Prevent Drastic Water Quality Changes
   • Remove uneaten food 30 minutes after each feeding; test ammonia/nitrite daily
   • Increase probiotic application frequency (2–3 times weekly) to break down organic waste accumulated in high temperatures
3. Physical Cooling Measures
   • Install shade nets (70%–80% shading rate)
   • Slowly add cool well water or cooled recirculated water to the pond surface in the afternoon (temperature difference ≤2°C)

IV. Strategies for Special Situations

1. Consecutive Extreme Heat (>35°C)
   • Implement "light fasting": feed low-protein wheat germ feed once every two days, at <0.5% of body weight
   • Add electrolyte supplements (e.g., aquatic multivitamins) to the water to alleviate osmoregulatory stress
2. Stuffy, Thunderstorm-Prone Weather
   • Suspend feeding when barometric pressure is low; resume only after water stabilizes (pH and dissolved oxygen recover) post-rain
3. Koi Showing Heat Stress Signs (gasping at surface, lethargy, increased mucus secretion)
   • Stop feeding immediately and increase aeration
   • Disperse vitamin C solution into the water (2–3 mg/L) to help combat stress

V. Health Monitoring and Record-Keeping

• Daily records: feeding amount, peak water temperature, koi feeding enthusiasm, fecal form (normal feces should be short, thick, and sink)
• Early warning: If feeding enthusiasm decreases by >50% for two consecutive days, check for parasite or bacterial infections