Fishes generally migrate for either feeding or for reproduction. Fish migration is very important because it provides proper environmental conditions for spawning, to put a stop in the extinction of the species. The significance of migration in fishes are: to find a suitable feeding and spawning ground, for protection from predators, to survive extreme climatic conditions, to increase genetic diversity, to survive and exist. Fishes migrate in different types on the basis of needs, and they are: Feeding migration, Spawning migration, Seasonal migration, Osmo-regulatory migration, Juvenile migration.
Migration Based on duration:
- Daily: Mainly for food gathering
- Annual: Mainly for reproduction
- Generational: Parent migrate to release eggs and die, their young ones migrate back to their homes
Factors influencing migration:
- Intensity and duration of light: Some fishes are attracted towards light and can be trapped by placing light at suitable points. Petromyzon and Acipenser
- Water current: Influences the direction of movement of migrate during night. fishes. Eggs and Fry are passively transported along with the current with feeding grounds. After spawning spent Salmon are carried by the river currents towards the sea.
- The stage of maturity of the Gonads and Endocrine Glands are also important factors governing migration.
Fishes often migrate in large groups for different reasons predominantly feeding and reproduction. These can be distinguished on the basis of their needs. They are:
- Alimentary or Feeding Migration: This occurs when the fishes’ food resources are exhausted, so they travel in search of feeding grounds.
- Gametic or Spawning Migration: This occurs during breeding season and is usually seen in fishes who have different spawning and feeding grounds that are far away from each other.
- Climatic or Seasonal Migration: This type of migration is usually seen in fishes from the arctic areas. In the winter, food becomes scarce and the temperature drops below zero; therefore, they must travel to warmer regions to avoid the extreme weather conditions.
- Osmo-regulatory Migration: This type of migration is from the sea to fresh water and vice-versa to maintain the balance of water and dissolved ions in their bodies.
- Juvenile Migration: This involves the larval stages of fishes. This occurs because the larvae hatch in the spawning grounds and have to migrate to their parent’s feeding grounds.
Different species of fishes follow different types of migration. They are:
- Diadromous Migration: This type of migration is seen in fishes that migrate between the sea and fresh water. These fishes are called true migratory fishes as fishes are usually restricted to either the sea or fresh water to maintain their osmotic balance. This type of migration can further be classified into two types:
- Anadromous Migration: usually seen in marine fishes like salmon that travel from the sea to fresh water predominantly for spawning purposes. This type is exclusively seen during breeding seasons.
- Catadromous Migration: this type is also generally only seen during breeding seasons. It is exhibited by fresh water fishes that travel from fresh water to the sea for spawning.
- Potamodromous Migration: this is exhibited by fishes that live in fresh water. These fishes travel upstream generally for spawning after which they return downstream to their feeding grounds. E.g., Carps, catfish, etc.
- Oceanodromous Migration: this type of migration is seen in fishes that live in the sea and migrate within the sea for feeding or spawning purposes. E.g., Tuna, cods, etc.
- Latitudinal Migration: as the name suggests, fishes that exhibit this type of migration travel from the north to south and vice versa. It is a type of climatic migration. E.g., In the spring, the sword fish travels north while in autumn, it travels south.
- Vertical Migration: this a type of daily migration from the floor of the water body to surface and vice-versa typically for protection, food or spawning. For instance, the sword fish may travel to the depths of the sea in search of food.
- Shoreward Migration: unlike other types of migration, this is migration of fish from water to land. This type of migration can be seen in eels as they migrate between different ponds through moist meadow grass.
Advantages of fish migration:
- In view of NIKOLSKY, migration is an adaptation towards abundance.
- The nursery or spawning ground may not have enough food to maintain both the mature and immature members of large population.
- Separate spawning, nursery and feeding grounds.
- Focuses the proper environmental conditions for spawning.
- Enhanced reproductive success.
Disadvantages of fish migration:
- In pursuing long journey, many migrating fish get lost. Most of them are eaten by predators.
By: Trisha Chang, Rakhi Singh, Roshni Manoj Kumar