Diel fluctuation

• Refers to fluctuation of temperature of water through the day due to solar hours.

Water temperature and fish growth

• The rate of biochemical processes in fish are temperature dependent.
• With increase in temperature, oxygen consumption increases and solubility of oxygen in water decreases.
• The release of nutrients by decomposition of organic matter at bottom is more at higher temperature with consequent increase in the nutrient status of water.
• Species might tolerate temperatures of 5-42⁰C, but the range for maximum growth might be from 25-30⁰
• Based on temperature tolerance fishes are divided into two groups:

1. Cold water fishes: Optimum temperature range is 10-20⁰C. Eg: Rainbow trout, Snow trout.
2. Warm water fishes: Optimum temperature range is 20-32⁰C. Eg: Chinese and indigenous major carps, catfishes, Tilapia.