Physiology of Finfish and Shellfish (2+1)

Principle

Dissolved CO₂ can be estimated at regular time interval for a sample of water with fish and the increase in the concentration of CO₂ can be taken as that released by fish.

CO₂ dissolved in water can be calculated by titrimetry. Following is the principle involved in CO₂ estimation.

CO₂ reacts with NaOH or Na₂CO₃as follows

2NaOH + CO₂ →Na₂CO₃ + H₂O

Na₂CO₃ + H₂O + CO₂→ 2NaHCO₃

These two reactions indicate the two possible methods for determining CO₂ in water. Titration with either standard NaOH (N/44)or standard Na₂CO₃ (N/22) to the phenolphthalein endpoint.