Answer:
The correct answer is - tend to lose water by osmosis since their internal salt concentration is lower than that of seawater.
Step-by-step explanation:
In freshwater fishes, the body of fishes has a higher salt concentration inside their body than the surrounding water, water enters through the osmosis process. Without any active regulation of this process, fishes would swell and get bigger and bigger. They have specialized cells called chloride cells in gills to take ions from water as they do not have kidneys.
In contrast, the marine fishes have a lower salt concentration in their body than surrounding water of sea or ocean and they lose water continuously and to compensate for this they need to drink water regularly.