Fish Migration
Migration is the
movement of animals over expansive distances and durations, driven by specific
purposes. Fish migration refers to the regular, often cyclical movement
of fish from one place to another, typically driven by environmental cues and
biological imperatives.
Among various species, fish exhibit diverse migratory behaviours,
occurring regularly and encompassing varied distances and timeframes, from
daily to annually. These journeys primarily serve the functions of feeding and
reproduction.
Causes
of Fish migration:
According to Northcote
(1978) causes of fish migration are
- To
optimize feeding
- To
avoid unfavourable condition
- To
enhance reproductive success
- To
promote colonization and exploit rich food source
Types
of fish migration based on their needs:
1. Feeding Migration or Alimentary migration: Occurs when fish seek
new feeding grounds due to resource depletion.
2. Gametic or Spawning Migration: Takes place during breeding seasons
as fish search for suitable spawning areas.
3. Climatic or Seasonal Migration: Involves movement to find favourable
climatic conditions.
4. Osmo-regulatory Migration: Occurs for maintaining water and electrolyte
balance, transitioning between sea and fresh water.
5. Juvenile Migration: Involves larval movement from spawning areas to
parental feeding habitats.
Fish
movement during migration can be categorized into:
1. Drifting Movement: Passive movement with water currents.
2. Dispersal Movement: Random locomotion from one habitat to various
directions.
3. Swimming Movement: Directed movement towards or away from stimuli.
4. Denatant and Contranatant Movement: Active swimming with or
against water currents, respectively.
Patterns
of fish migration include:
1. Diadromous Migration: It is the migration of fish between the sea
and fresh water.
- Anadromous
Migration: Marine fish migrate to freshwater
for spawning (e.g., salmon).
- Catadromous
Migration: Freshwater fish migrate to the sea
for spawning (e.g., eels).
- Amphidromous
migration: Diadromous fishes migrate from
freshwater to the sea or sea to freshwater (e.g. Gobies).
2. Potamodromous
Migration: Limited to freshwater habitats for feeding or spawning (e.g.,
carps, catfish).
3. Oceanodromous Migration: Movement within the sea for feeding and
spawning (e.g., clupea, tuna).
4. Latitudinal Migration: Migration from north to south or vice
versa, driven by climatic factors (e.g., swordfish).
5.
Vertical Migration: Daily movement between deep and surface
waters for various purposes (e.g., swordfish).
6.
Shoreward Migration: Temporary movement from water to land
(e.g., eels migrating via moist meadow grass).
Duration
of Fish Migration:
Fish migration can vary
greatly in duration, from short, daily movements to long, seasonal migrations.
Some migrations occur
annually, triggered by seasonal changes in temperature, daylight, or water
flow.
Others may be tied to
specific life stages, such as spawning migrations that occur once or twice in a
fish's lifetime.
Factors
Influencing Fish Migration:
Environmental
cues: Fish often migrate in response to changes in
temperature, water flow, photoperiod, and food availability.
Reproduction:
Many species migrate to spawn in specific breeding grounds where conditions are
optimal for egg fertilization and larval survival.
Feeding:
Some fish migrate to areas with abundant food resources, optimizing their
feeding efficiency.
Habitat
quality: Degradation or alteration of habitats can disrupt
migration patterns, affecting fish populations and ecosystem dynamics.
Predation:
Avoidance of predators or seeking areas with reduced predation pressure can
drive migration behaviour.
You can also read about
Mechanisms of Fish Migration:
Olfactory
cues: Fish possess a keen sense of smell and use chemical
cues to navigate towards spawning grounds or feeding areas.
Magnetic
orientation: Some species may use the Earth's
magnetic field for navigation during migration.
Sun
compass: Fish can also utilize the position of the sun in
the sky as a reference point for navigation.
Hydrodynamic
cues:
Sensing changes in water flow and pressure helps fish navigate river systems
and ocean currents.
Genetic
predisposition: Inherited traits and instincts play a
significant role in guiding migration routes and behaviours.
Methods
for Studying Fish Migration:
Tagging
and tracking: Researchers use various tagging
techniques, including acoustic tags, radio tags, and satellite tags, to monitor
fish movement.
Hydroacoustics:
Sonar technology allows scientists to detect and quantify fish populations in
rivers, lakes, and oceans, providing insights into migration patterns.
Genetic
analysis: DNA sampling helps identify population structure,
genetic diversity, and migration routes of fish species.
Remote
sensing: Satellite imagery and aerial surveys can be used
to observe large-scale migration patterns in marine environments.
Behavioural
observations: Direct observation, underwater
cameras, and fish traps provide valuable data on migration behaviors and
habitat preferences.
Significance
of Fish Migration:
Ecosystem
health: Fish migration facilitates nutrient cycling, energy
transfer, and biodiversity maintenance within aquatic ecosystems.
Fisheries
management: Understanding migration patterns is
essential for sustainable fisheries management, ensuring the conservation of
fish stocks and ecosystems.
Cultural
and economic importance: Many societies depend on migratory
fish species for food security, livelihoods, and cultural traditions.
Ecosystem
connectivity: Migration connects different habitats
and ecosystems, promoting species diversity and resilience to environmental
changes
