Pisces: Migration | Zoology Optional Notes for UPSC PDF Download

Migration of Fishes

• Jones defines migration as a movement class prompting migrants to return to their region of origin.
• Baker suggests a return journey is not necessary.
• Dingle defines fish migration as a special behavior evolved for spatial displacement.
• Accidental or unintentional movements are not considered migration.

• Several mature fish species migrate for breeding or feeding, including the cod, salmon, Pacific salmon, herring, tunas, European eel, American eel, Japanese eel, Australian eel, hilsa, three-spined stickleback, flatfish, mackerel, lamprey, and others.

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Types of Migration

• Climatic Migration: Seeking better climatic and environmental conditions.
• Gametic Migration: Undertaken for spawning.
• Alimental Migration: In search of food and water.
• Osmoregulatory Migration.

• Periodicity of Migration:

  • Occurs at regular intervals - daily, monthly, seasonally, yearly, or after a long gap, depending on biotic and abiotic factors.
  • For example, Petromyzon larvae may live in mud for years before migrating to sea; eels may remain in fresh water for years before spawning in the sea; Pacific salmon returns to spawning grounds after years at sea.

• Distance, Speed, and Duration of Migration:

  • Varies between species, influenced by the environment.
  • Some cover long distances with varying speeds and durations, depending on factors like food gathering during the journey.

• Methods of Migration:

  • Drifting: Passive travel with water currents.
  • Random Locomotory Movement: In a uniform environment, fish spread out in all directions by random locomotory movements.
  • Orientated Swimming: Swimming in a particular direction, towards or away from a source of stimulation.

Migration showcases diverse behaviors, adaptations, and purposes, making it a complex and varied phenomenon in the life of fish species.

Patterns of Migration

Migration patterns in fishes are diverse, exhibiting various adaptations to different environments and life stages. Here are some key patterns:

• Anadromous: Species with feeding areas in the ocean but migrate to freshwater rivers for spawning. Examples include salmon, trout, hilsa, and lampreys.
• Catadromous: Spend part of their lives in freshwater but migrate to the sea for spawning. The European eel is a prominent example.

• True migratory fishes within freshwater environments, such as carps and trout. They migrate long distances in rivers to find suitable spawning grounds.

• Truly migratory marine fishes traveling long distances in the sea to spawn and later returning to feeding areas.
• Examples include cod, herrings, mackerels, and tunas.

Migration Types

• Vertical Migration: Daily movement between deep and surface waters, often related to feeding. Seen in species like Atlantic herrings.
• Seasonal Migration: Undertaken during specific seasons, such as spawning migrations.

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Migration Cycles

• Herrings (Clupea): Exhibit both daily vertical migration for feeding and seasonal migration for spawning near the coast. Larvae drift to wintering areas.
• Cod (Gadus morhua): Spawn at the sea bottom, and the young ones feed on zooplankton. The migration cycle is completed before spawning at around five years of age.
• Flat Fish (Pleuronects platessa): Inhabit coastal waters of Europe. Pelagic eggs and larvae drift to nursery areas, and young ones migrate to the bottom to feed.
• Tunas (Thunnus spp.): Warm-blooded fishes with wide distribution. They spawn in the Mediterranean Sea, undergo migration cycles through the Strait of Gibraltar, and return for spawning.

Migration in fishes involves complex life cycles, adaptive behaviors, and responses to environmental cues. The variety of patterns reflects the diverse ecological niches and challenges faced by different species.