Fry fish cannot tolerate more than which concentration of chlorine?

• A. 0.01 ppm chlorine
• B. 0.1 ppm chlorine
• C. 0.001 ppm chlorine
• D. 0.02 ppm chlorine

Answer: (A)

Chlorine is highly toxic to fish, and fry are especially vulnerable because their gills are still developing and they have limited ability to cope with chemical stress. Even very small amounts of chlorine can irritate or damage gill tissue, hinder respiration, and lead to stress or death in fry. Because of this, water used for fry needs to be dechlorinated to essentially zero chlorine before they are introduced. In practice, the safe threshold cited for fry is extremely low—around one hundredth of a part per million. Levels higher than this increase risk and can harm the young fish. The other options imply chlorine concentrations well above that safe limit and would not be acceptable for stocking fry.