Question

Consider the following statements:
Statement-I: Salmon and Hilsa are catadromous fishes.
Statement-II: In limnetic zone rate of photosynthesis and rate of respiration are almost equal.
The correct answer is

• A. Both statements I and II are true
• B. Both statements I and II are false
• C. Statement I is true, but statement II is false
• D. Statement I is false, but statement II is true

Hint:

{Migration Mnemonics:}

• {A}nadromous: {A}scending the river (Salmon).
• {C}atadromous: {C}oming down to sea (Eel).

Answer 1

The Correct Option is B

Step 1: Analyze Statement I:
Salmon and Hilsa are marine fishes that migrate up rivers to spawn in fresh water. This migration from Sea to River is called Anadromous migration. Catadromous migration (River to Sea) is seen in fishes like the Eel (\Anguilla). Thus, Statement I is False.
Step 2: Analyze Statement II:
The Limnetic zone refers to the open, well-lit surface waters of a lake, away from the shore. This is the primary zone of production where photosynthesis (P) by phytoplankton typically exceeds respiration (R) (i.e., $P>R$). The point where $P = R$ is specifically called the compensation depth, which marks the lower boundary of the euphotic zone, but the limnetic zone as a whole is a net producer. Therefore, stating that P and R are equal in the limnetic zone is generally False (except at the specific compensation boundary).
Step 3: Conclusion:
Since both statements are factually incorrect, Option (B) is the appropriate answer.