FISH MIGRATION

1. SALIPUR AUTONOMOUS COLLEGE ,SALIPUR
ZOOLOGY DEPARTMENT
TOPIC-MIGRATION IN FISHES
NAME-SONALI GHOSAL
+3 3RD YEAR SCIENCE

2. MIGRATION IN FISHES
INTRODUCTION:-
 Migration is a movement from one habitat to another as
conceived by many ,including South wood(1962).
 According to Baker(1978)it is the ‘’act of moving from one
spatial unit to another .
 The animal thus changes the conditions of life by
undertaking migration
 According to Nikolsky(1963)migration is an adaption
towards increasing the abundance of a species.
TERMS USED TO DESCRIBE FISH MIGRATION
 Meek(1915)for the firstime introduce two terms denatant
and contranatant to describe the movements of fish in
relation to the water current.
 Denatant is swimming ,drifting or migrating with water
current,but contranatant means swimming or migration
against water current.

3.  Pre spawning migrations are active contranatant
movements against water current ,while post spawning
migrations are passive denatant movements with the
current.
 Myers term and description are as follows-
(1)DIADROMOUS:
 These are real migratory fishes.
 They migrate between the sea and fresh water.
 They basically belongs to following categories:
(a)ANADROMOUS:-
 These are diadromous fishes which spend a major part of
their lives in the sea but migrate to fresh water during
breeding period for spawning particularly.
 Several marine fishes like salmon Hilsa travel a long
distance in the sea and reach the rivers to spawn in the
fresh water.

4.  After egg laying they return to their feeding places in the
sea.
 Hilsa ilisha resides in the Bay of Bengal. During the
breeding period they ascend the estuaries of the Ganges
and reach fresh water.
 They used to migrate from Bay of Bengal and regularly
reached as far as Allahabad through the river Ganges.
 But now because of the construction of Farraka barrage on
the Ganges in Bengal the migration of Hilsa has been
restricted.

6. (b)CATADROMOUS:-
 These are diadromous fishes which spend a major part of
their lives in fresh water and migrate to the sea to breed.
 The fresh water eel Anguilla anguilla travels several
thousand miles in reaching the sea ,starting from the river.
 They lay their eggs in the sea .
 The young larvae swim back towards the fresh water.
 They undergo metamorphosis and changes from
Leptocephalus stage to Elevers.
 They become adult in fresh water and after obtaining
maturity they start sea ward again.

8. (c)AMPHIDROMOUS:-
 These are diadromous fishes which migrate from fresh
water to sea or vice-versa not for the purpose of breeding
but it is a regularity at some definite stages of their life
cycle.
Ex-Gobies

10. (2)POTAMODROMOUS:
 These are all migratory fishes but their migration remains
confined to fresh water only .
 Carps and Trouts travel long distances for the purpose of
spawning.
 After egg laying they return back to the feeding ground
again.
 Thus migration occurs wholly within fresh water .
Carp

12. (3)OCEANODROMOUS:
 These fishes live and migrate wholly in the sea .
 Herrings and Mackerels are the common examples.
 They travel long distances in the sea and after laying their
eggs at suitable places return to their feeding ground.
 The word spawning bed,spawning ground and spawning
area have different meaning.
 In the case of fish with demersal eggs, the spawning bed is
the actual site of egg laying.
 Numerous beds are located within the specific spawning
ground.
 Within a spawning area there may be more than one
spawning ground.

13. Herrings
Mackerels

14. TYPES OF MIGRATION AND MIGRATORY MOVEMENTS:
 Fish can move in vertical direction or in a horizontal direction
either up stream or down stream.
 When fish move from one place to another in search of food
and suitable water,it is known as alimental migration.
 Migration for the purpose of reproduction is known as gametic
migration .
 The migration for securing a suitable climatic condition or a
better climatic condition is known as climatic migration.
 For maintaining the water salt balance (homeostasis)there may
be osmoregulatory migration.
 To reach their destination,fish adopt various method for making
migratory movements.
 Drifting is a passive movement when fish are carried by water
currents.
 When fish are released from a particular point and spread out in
all directions leading to uniform distribution of the species (by
dispersal)-this is known as random locomotory movement.

15. MIGRATION AND HOMING:
 The periodic and directed travel mainly for
feeding,breeding and overcoming adverse cliamatic
condition is said to be migration.
 Homing has been defined as ‘’the return to a place
formerly occupied by the migrants instead of going to
another equally probable places’’.
 Several workers believe in the olfactory hypothesis as
sensory basis for homing in salmonids.
 Pheromones and non-pheromones play a vital role in
migration and homing.
 The ground water seepage hypothesis developed by
Harden Jones illustrate that the spawning area and the
spawning ground of marine fishes spawn in coastal water
can be identified with chemicals which enter the sea by
ground water seepage.

16.  FACTORS INFLUENCING MIGRATION:
 There are several physical, chemical and biological factors
which influence migration.
 The physical factors are depth of water,bottom
materials,pressure,temperature,intensity of light ,photoperiod
,nature of water current and turbidity etc.
 The characters like salinity,pH of water concerned,smell and
taste of water are some of the important chemical factors.
 The biological factors are include food memory,sexual
maturity,physiological clock and the endocrine glands .
 Presence or absence of predators and competitors may also
be considered as biological factors.
 Baggerman (1962)has suggested that gonadal hormone play
an important role in the migration of anadromous fishes .
 Rising temperature of the sea during summer season
provides a stimulus to Salmon for seaward migration.

17.  When the temperature of river water rises ,fishes move up
streaming for spawning.
 Several fishes can not tolerate salinity change and such fishes
are called stenohaline.
 So,for this reason they donot undertake large migrations,and as
such,they are confined to fresh water only.
 On the contrary,some fishes like
Anguilla,Salmon,Hilsa,Gastrosteus and Fundulus etc are capable
of adapting themselves to large salinity changes and they are
called euryhaline.
 They can easily undertake large scale migrations.
 The intensity of light and also duration of light play important role
in the migration of fish.
 Migration of Herrings can be seen during full moon.
 Robertson et.al. (1961)have reported high levels of
corticosteroids in the plasma of migrating and spawning Salmon .
 The thyroid gland has been implicated in migratory processes .

18.  For osmoregulation in sea-water gill Na+,K+-ATPase is an
important enzyme.
 Prolactin also plays an important role in the control of
water and sodium movement in fresh water. Corpuscles of
stannius also play some role in the migratory fishes.
Fundulus