Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): The rohu hatchlings gulp the food item after couple of days
Reason (R): Mouth in the hatchlings of rohu is developed after one day of hatching
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Carp hatchlings do not have open mouths at hatching. They are yolk-sac larvae and only begin external feeding after the mouth opens and the yolk sac is absorbed.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Indian Major Carps (IMCs), such as rohu (*Labeo rohita*), undergo rapid anatomical changes during their early larval stages before they begin feeding externally.

Step 2: Detailed Explanation:
- Assertion (A): Immediately after hatching, rohu larvae are called hatchlings and are not yet capable of feeding. They rely on their yolk sac for nutrition. After approximately 2 to 3 days (depending on water temperature), their yolk sac is largely absorbed, and they begin active external feeding by gulping small organisms, such as rotifers. Thus, Assertion (A) is true.
- Reason (R): The mouth of a rohu hatchling is closed and non-functional at the time of hatching. It typically opens and develops about 24 hours (one day) post-hatching, and the digestive tract becomes functional shortly thereafter. Because the mouth takes time to develop and open, hatchlings cannot feed immediately upon hatching and must wait a couple of days before they start gulping food. Thus, Reason (R) is true and directly explains the delay described in the Assertion.

Step 3: Final Answer:
Both statements are true, and the development timeline of the mouth explained in the Reason is the correct explanation for the feeding latency mentioned in the Assertion.