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Q111 (CAPF/2011) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Animal diversity behaviour Answer Verified

If a healthy freshwater fish is placed in saltwater, the fish

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Your answer: —  Â·  Correct: A
Explanation

When a healthy freshwater fish is placed in saltwater, it enters a hyperosmotic environment where the external salinity is significantly higher than its internal body fluids [t1][t2]. Freshwater fish are typically hypertonic to their natural environment, meaning they have higher salt concentrations than the surrounding water and must constantly excrete excess water [t2]. However, in saltwater, the osmotic gradient reverses. Through the process of osmosis, water is drawn out of the fish's body—primarily through the permeable gill epithelium—to the more saline environment [t1][t5]. This leads to severe cellular dehydration as the fish loses its internal water balance [t1]. Most freshwater fish are 'stenohaline' and cannot tolerate such rapid shifts in salinity, resulting in physiological stress and death due to the inability to maintain osmotic homeostasis [t1][t5].

Sources

  1. [1] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/osmoregulation
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