Types of Migration in fishes and factors influencing migration

Generally, fishes move within restricted territorial limits and do not go out of their home range. However, a few species travel long-distance sometime moving from fresh to seawater or vice versa. This movement of fishes is known as migration in fish.

TYPES OF MIGRATION

Migration in fishes can be of the following types:-

BASED ON THE PURPOSE OF MIGRATION

On the basis of migration the fishes can be classified into the following categories

• Alimental migration

Alimental migration are those migrations in which the fishes are migrated from one place to another in search of food and water.

• Gametic  Migration

In Gametic  migration, fishes are migrate from one place to another for the purpose of  reproduction.

• Climatic migration

When the fishes migrate from one place to another place for securing more suitable climatic conditions then migration is known as climatic migration.

• Osmoregulatory  Migration

This type of migrations are facultative and do not occur regularly.

BASED ON THE HABITAT

Diadromous   Migration

This is the true migration in which fish migrate between the sea and freshwater. It can be of the following three types:-

• Anadromous  migration

In anadromous migration, the marine fishes migrate to freshwater spawning. A single species of Atlantic Salmon - Salmon salar and five species of Pacific Salmon – Oncorhynchus  exhibit anadromous migration.

During winter, both the sexes start migrating from their feeding ground (sea) to freshwater mountain streams to their breeding ground. They stop feeding, change to dull reddish-brown from silver. Salmons then make a crude nest by excavating a shallow saucer-shaped pit in the bottom gravel. After spawning the adults die. In some Atlantic species of Salmon, a few adults may survive.

EXAMPLE:- Fishes like Salmon, shad , sea lamprey and Hilsa, sturgeon and some trouts, Acipenser and Alosa all exhibit anadromous migration.

• Catadromous migration

It is shown by those diadromous fishes  which  feed and become reproductively mature in freshwater but migrate to the sea for laying eggs or spawning. The famous example of catadromous  migration is freshwater eel Angulia. It travels several thousand miles starting from its feeding grounds, the European freshwater rivers to reach its spawning grounds in the Sargasso Sea off Bermuda.

• Amphidromous migration

 These diadromous fishes migrate from the sea to freshwaters or from freshwaters to sea. The purpose of migration is not breeding. This occurs regularly at some definite stage of life cycle other than a reproductive season. Gobies are said to exhibit amphidromous migration.

• Patomodromous  migration

It includes migration of fishes from freshwater to freshwaters example carps and trouts travel long distances in large rivers in search of spawning grounds. After laying eggs these return to the feeding ground.

• Oceanodromous migration

It is migration of marine fishes from one place to another in the ocean. Many marines fishes like Clupea(herring), Scomber (mackerel), Thunnus (Tuna) travel long distance in the sea for laying eggs.

BASED ON DIRECTION

• Latitudinal migration

It is shown by barracudas (Sphyrna) and Sword fishes (Xiphius gladus). The fish move towards the north in spring and south in autumn.

• Vertical migration

It is shown by deep water fishes, which move up and down daily.

Significance of migration in fishes

As indicated by Nikolsky relocation is an adjustment towards plenitude. The  spawning and nursery grounds may not have enough food to support both the larvae and adult members of a large population . Hence there is a separation of spawning, nursery and feeding grounds achieved by migration.

A return to the parent spawning ground is another explanation for migration. IT is may be of some advantage to a species to those under which they themselves survived when young. It ensures a better egg and larval survival.

 FACTORS INFLUENCING MIGRATION

Migration in fishes is influenced by various physical, chemical, environmental and biological factors:

• Physical  Factors

These include depth of water, pressure, temperature, light intensity, photoperiod, current, turbidity and the nature of the bottom, etc.

• Chemical  Factors

These include salinity, ph, smell and taste of water.

• Biological Factors

These include food, oxygen, blood pressure, sexual maturity, biological clock, physiological clock, endocrine gland  and memory etc.

Presence or Absence of predators and competitors also influence migration or movement from one place to other.