2. (i)To avoid unfavourable conditions: light,
temperature, pH, water currents
(ii)Breeding
(iii) To enhance the survival of offspring's
(iv) Scarcity of food in feeding areas
(v)Population pressure (competition and predation)
3. To find suitable feeding and spawning ground
To protection from predators
Survive from extreme climatic conditions
To survive and existence for increasing genetic diversity
5. 1. Diadromous – Travel between sea & fresh water
a) Anadromous (most of life at sea, breed in fresh
water) - from sea water to fresh water (marine fishes)
Eg. Salmons, Indian shad
b) Catadromous (most of life in fresh water, breed at
sea) - from fresh water to sea water for spawning
(fresh water fishes) Eg. Eels
2. Amphidromous – migrate between water types at
some stage other than breeding
3. Potamodromous – Migrate within a fresh water
system - long movement within fresh water. Eg. Carps,
trouts.
4. Oceanodromous (Migrate to different regions of the
ocean) – from native place to a far off place. Eg. Tunas,
mackerels
6. 1. Anadromous Migration
Fishes which migrate from the sea into fresh
water to spawn
Ones which stay entirely in sea water and
migrate upstream to spawn
Anadromous fish, born in fresh water, spends
most of its life in the sea and returns to fresh
water to spawn
Adults usually die after spawning
Their adaptations to conditions of different
habitats are particularly with regard to salinity
of the water
Common examples - Salmon, Trout, Hilsa,
striped bass, Sea lamprey and sturgeon
7. 2. Catadromous Migration
Catadromous fishes are ones which migrate
from fresh water into the sea to spawn e.g. eels
of the genus Anguilla (19 species)
It travels several thousand km starting from
rivers reaching spawning grounds in sea
After spawning adults die
Larvae of eel drift from spawning grounds, takes
several months to 3 years, to reach river &
undergo metamorphosis to become adults
Young ones are born in the ocean, mature in
freshwater or estuarine habitats, and return to
the ocean to spawn
8. 3. Potamodromous Migration
The movement is confine to fresh water - e.g. carps,
trouts, catfishes
Travels long distances in rivers to locate suitable
spawning grounds (upstream or downstream)
After laying eggs, the parents return to the feeding
area as food is available only for the young ones &
cannot support the adults
Migration may also be - Competition due to increase
in population
Scarcity of food may also force fishes to migrate
other places, where food is abundant
9. 4. Oceanodromous Migration
Travel long distances with in sea to spawn & return
to the feeding areas
There are no barriers within the sea and fishes have
learned to migrate in order to take advantage of
favourable conditions wherever they occur
They differ mainly from one another by the extent of
their migration
Examples- Mackerels, Tunas, Cod, Herrings
During migration these species visit spawning areas,
nursery areas, feeding areas, winter area etc.,
10. Migration of Herring
North Atlantic and North pacific Oceans and exhibit
seasonal or annual spawning migration to the
spawning ground near the coast
After spawning , the larvae drift along the water
current to wintering area near the coast, where they
feed and grow
On becoming adult, they join the older fish in
migration cycle and return to spawning area when
mature
This takes 4-6 years
11. Factors influencing migration
Influenced by
Physical factors
a) Temperature
b) Light intensity
c) Photoperiod
d) Water current
e) Turbidity
f) depth
In sea water rise in temperature provides
stimulus to Salmon for Migration.
In fresh water temperature rise fishes moves
upstream for spawning
12. Factors influencing migration
Chemical factors
a) pH
b) Salinity
c) Odour
d) Taste of water
Salinity of water restricts the movement of fishes.
Freshwater species are stenohaline (intolerant to
large salinity changes).
Hence they remain confined to fresh water do not
undertake migration involving long distances
But some species like Salmon, Hilsa, Anguilla are
euryhaline and can adjust to large salinity variations
i.e. Diadromous fishes
13. Factors influencing migration
Biological factors
a) Food
b) Memory
c) Stage of sexual maturity
d) Predators and competitors
e) Hormones
Availability of food is the primary factor for
the survival of juveniles
Memory guides some species during
migration e.g. Salmon returns to the same
area of river for spawning, where its own
hatching & development took place
14. Role of Hormones in migration
Observed in Diadromous fishes
The osmo and ionic regulation in these
species is controlled by Hormones secreted
by the pituitary gland e.g. Prolactin,
Corticotrophin, growth hormone
Prolactin is the most important hormone that
acts on gills, skin, kidney, urinary bladder
and the intestine and influence the water and
ion regulation
It also reduces the loss of Na ions in the
fresh water fishes (Eel)
