Question

In which of the following habits do catla and rohu inhabit?
A. Oceans
B. Fresh water
C. Lagoons
D. Estuaries

Answer 1

Hint: Rohu occurs mostly in the rivers of Northern and Eastern India, Pakistan, and Bangladesh. Moreover, Catla is a fish found mostly in the rivers and lakes of Northern India, Bangladesh, and Pakistan.

Complete answer:
Freshwater fishes are those fishes that reside in rivers, lakes, and ponds and have very low levels of salinity of about less than 1%.They have different morphological adaptations to survive in freshwaters of rivers and lakes. The salts they need are retained inside their bodies inside their bodily fluids. Their gills must be able to diffuse essential dissolved gases as well. Due to osmolarity differences, water tends to enter their bodies. As a result, they are provided with a large number of scales which help them to prevent this. Because of this, fishes whose most of the scale has been lost tend to die. They are equipped with highly developed kidneys that retain salts in their bodies before excretion of urine. On the other hand for saltwater fishes, water tends to enter their bodies due to a high concentration of salt outside. Thus they drink saltwater and expel it through their gills. They have specialized kidneys and ionic pumps that expel salts from their bodies. As these physiological conditions are not found in fishes like Catla and Rohu, they are freshwater fishes.

Hence, the correct answer is option (B).

Note: Rohu and Catla when placed in a saltwater aquarium, die. This occurs due to a change in their environmental osmolarity. By remembering this simple phenomenon, you can get the answer to the above question.