Question

Mullets, bhetki, pearl spots, prawns, mussels are the examples of
A. Marine fish
B. Freshwater fish
C. Finned fish
D. Shellfish

Answer 1

Hint: The given fish spend most of their lives in rivers, lakes, ponds, etc. with a salinity of water less than \[1.05%\]. These fishes prefer low salinity environments. They have various physiological adaptations to survive in these water environments. These fish have more scales, specialized gills, and well-developed kidneys.

Complete answer:Mullets, bhetki, pear spots, prawns, mussels are fishes that prefer low salinity water of lakes, rivers, ponds, etc. these are freshwater fishes as they can tolerate salinity levels up to \[1.05%\]. These fish have great economic importance as they contribute to the growth of the economy of the region where they are found. During the 1990s the production of freshwater fish surged and contributed a good part to economic growth.
Freshwater fishes have different physiological adaptations as compared to marine water fishes. These fish have specialized gills that keep the body salts inside while diffusing the dissolved gases. The scales of these fish help reduce the diffusion of water through the skin. Freshwater fish may die if they lose too many scales. The kidneys of freshwater fish are well developed as they function to reclaim salts from the body before excreting wastes. Freshwater fish can further be divided into coldwater fish, cool water fish, and warm water fish.
Human mediated anthropogenic reconstruction and routing of waterways affect the streamflow of rivers. It also affects the temperature and normal habitat conditions of freshwater bodies. This leads to habitat destruction of freshwater fish. Thus, these activities should be performed carefully without harming the fish populations.

So, the right answer is option B.

Note: Freshwater fishes are vulnerable to many invasive species. Most of the fish reproduce and lay their eggs in freshwater bodies. Sometimes these eggs hatch and become inhabitants of the water body. They may be predatory to the native freshwater fish and cause their extinction. One such example is the introduction of rainbow trout in Twin Lake of Colorado. This led to the extinction of yellow cutthroat fishes in that area.