Q.25 A fish that spends its adult life in seawater but migrates to the freshwater for
spawning is
1.catadromous
2.anadromous
3.Limnodromus
4.oceanodromous
Anadromous fish exemplify diadromous migration, living most of their adult lives in seawater before returning to freshwater rivers for spawning, as seen in salmon species. For Q.25—”A fish that spends its adult life in seawater but migrates to the freshwater for spawning is”—the correct answer is option 2: anadromous.
Option Analysis
Option 1: Catadromous
Catadromous fish hatch in seawater, migrate to freshwater for growth and maturation, then return to the ocean as adults to spawn (e.g., eels like Anguilla). This is the reverse pattern of the query.
Incorrect, as adults spawn in saltwater, not freshwater.
Option 2: Anadromous
Anadromous fish (Greek: “upward-running”) are born in freshwater, migrate to sea as juveniles for feeding/growth, and return to natal rivers as adults to spawn (e.g., salmon, sturgeon, striped bass). Seawater provides abundant food, while freshwater offers safer egg incubation.
Correct; matches the description precisely.
Option 3: Limnodromous
“Limnodromous” (lake-running) refers to fish migrating within entirely freshwater systems, such as between lakes and rivers, without involving seawater (e.g., some African rift lake cichlids). Not a standard term for marine-freshwater transitions.
Wrong; no saltwater phase described.
Option 4: Oceanodromous
Oceanodromous fish undertake long migrations entirely within the ocean, never entering freshwater (e.g., some tunas or billfishes moving between spawning and feeding grounds). Purely marine lifestyle.
Incorrect; lacks the freshwater spawning migration.
Migration Types Comparison
| Type | Adult Habitat | Spawning Habitat | Examples |
|---|---|---|---|
| Anadromous | Seawater | Freshwater | Salmon, shad |
| Catadromous | Freshwater | Seawater | Eels |
| Oceanodromous | Seawater | Seawater | Tunas |
| Limnodromous | Freshwater | Freshwater | Lake migrants |
These patterns evolved for optimal juvenile survival: freshwater protects eggs from predators/currents, while marine waters offer superior nutrition.
Exam Relevance
Critical for CSIR NET/GATE Zoology: Distinguish anadromous (sea→river) from catadromous (river→sea). Note semelparity in many anadromous species (die post-spawning). Dams disrupt migrations, impacting conservation.
