Question

If a sweet water fish enters a sea, the fish will:
(A) Swell
(B) Be squeezed
(C) Remain as it is
(D) Suffer none of these

Answer 1

Hint
From the options we can elucidate that the question is related to the pressure differences in sea water and fresh water. So, here we should try to observe what pressure difference there would be if the fish enters from fresh water to sea water.

Complete step by step answer
Since there are salts dissolved in sea water than any other water bodies such as river, pond etc. the sea water is denser than the fresh water and pure water. This is because the dissolved salts in seawater increase the mass in effect than its contribution to the volume, and thus the density increases. Now, if we assume that the fish from the river enters the sea water at the same depth, then the pressure should be varying because the sea water is denser than the fresh water. But as per the equation for the liquid pressure, we can understand that the pressure at the seawater will be more than that in freshwater/river if the depth is the same, because the seawater is denser. Thus, due to the higher pressure, there is a chance that the fish gets slightly squeezed, when entering the sea.
Therefore the correct answer is option (B).

Note
In the actual situation, the freshwater fishes that travel into the seawater require a few acclimatization techniques, because of the pressure, salt content of the water etc. Such fishes like Salmons, prepare themselves for making their body suitable for living in the seawater and these biological changes do happen automatically within a few days.