Step 1: Understanding the Concept:
Many fish species exhibit migratory behavior between different aquatic environments to complete their life cycles.
Fishes that migrate between saltwater (sea) and freshwater (rivers) are called Diadromous fishes. There are two primary categories:
1. Anadromous (Greek: 'ana' = up): These fishes live in the sea as adults but swim up into freshwater rivers to spawn (lay eggs).
2. Catadromous (Greek: 'kata' = down): These fishes live in freshwater as adults but swim down to the sea to spawn.
The reasons for these migrations usually involve finding safer environments for juveniles or richer food sources for adults.
Step 2: Detailed Explanation:
Let's evaluate the fish mentioned in the options:
- Labeo (Option A): Such as {Labeo rohita} (Rohu). This is a purely freshwater carp. It lives, feeds, and breeds in rivers and ponds. It does not migrate to the sea.
- Channa (Option D): Known as Snakeheads. These are also freshwater fish found in ponds and rivers. They are not known for marine-to-freshwater migrations.
- Anguilla (Option C): The freshwater Eel. This is the most famous example of a Catadromous fish. The adults live in the rivers of Europe and America, but they migrate thousands of miles to the Sargasso Sea (Atlantic Ocean) to spawn and die.
- Hilsa (Option B): {Tenualosa ilisha} (Hilsa) is a marine fish found in the Indian Ocean. Every year, during the monsoon season, millions of Hilsa fish migrate hundreds of kilometers into the Ganges, Padma, and Godavari rivers to spawn in the freshwater. This behavior makes it a classic Anadromous fish. Another well-known global example is the Salmon.
Since the question asks for an anadromous fish, Hilsa is the perfect match.
Step 3: Final Answer:
Among the choices, Hilsa is the anadromous fish that migrates from the sea into freshwater for spawning.
The correct option is (B).