Step 1: Understanding the Concept:
Constitutional division of legislative powers in Indian fisheries: Entry 21 of the State List (List II, Seventh Schedule of the Constitution of India) assigns fisheries within territorial waters (up to 12 NM) to the State Governments.
Key Formula or Approach:
\[ \text{7th Schedule: } \underbrace{\text{Inland \& Territorial Waters (0--12 NM)}}_{\text{List II (State List) - Entry 21}} \quad \longleftrightarrow \quad \underbrace{\text{EEZ / Deep Sea (12--200 NM)}}_{\text{List I (Union List) - Entry 57}} \]
Step 2: Detailed Explanation:
Under the Constitution of India (Seventh Schedule, Article 246):
1. State List (List II), Entry 21: Explicitly designates 'Fisheries' as a State Subject (C). Consequently, all inland water bodies (rivers, lakes, reservoirs, ponds) and coastal marine fisheries within Territorial Waters (from coastline up to 12 nautical miles) fall exclusively under the administrative, regulatory, and legislative jurisdiction of coastal State Governments (enforced via State Marine Fishing Regulation Acts [MFRA]).
2. Union List (List I), Entry 57: Covers 'Fishing and fisheries beyond territorial waters' (the Exclusive Economic Zone [EEZ], $12 - 200\text{ NM}$), which is governed by the Central Government.
Step 3: Final Answer:
Therefore, fisheries within territorial waters is a State subject, corresponding to option (C).