Answer:
The correct answer is fluid friction.
Step-by-step explanation:
During swimming in the water, the fish has to encounter with a drag resulting due to fluid friction. In order to swim effectively, a fish needs to use its strength in order to pass through the resistance resulting due to friction. In the case of clean waters, where the water is thin, thus, the swimming becomes much smoother. However, in murky waters, the fish has to encounter with more friction, thus, making the process of swimming tough.
Apart from liquids, the fluid friction term can also be used to illustrate friction resulting due to gases like nitrogen and oxygen.