Zoology /Fish Biology

2. Migration
• The movement of large number of fishes for
the purpose of feeding or spawning, is known
as migration.
• It may take place in vertical direction, as from
the deeper to the surface water, or it may be
in horizontal direction, either upstream or
downstream.

3. Migratory Fishes
Common name Scientific name
Pacific Salmon Oncorhynchus spp.
Tunas Thunnus
Hilsa Hilsa ilisha
Lamprey Petromyzon marinus
Mackerel Scomber spp.
American eel Anguilla rostrata
Herring Clupea harengus

4. Types of Migration
Migration can be of anyone of the following
types :
• Climatic migration , undertaken to search
better climatic and environmental conditions.
• Gametic migration is undertaken for
spawning.
• Alimental migration is undertaken in search of
food and water .

5. Methods of Migration
• Several methods can be used by a species for
migration ,
These are :
• By drifting : Fishes travel passively with the water current
and do not make any effort .This is called ‘drift and results in
‘directional movement ’ by the fish .
• Random Locomotory movement : In a uniform environment
,fish released at a point spread out in all directions by
random Locomotory movements ,this results in uniform
distribution or dispersal of the species .
• Orientated Swimming : This evolves swimming in a particular
direction ,which may be either towards or away from the
source of stimulation .This can also be at an angle between
the fish and the source of stimulation .

6. Patterns of Migration
1. Diadromous Fishes: These are truly migratory fishes
which move between sea and freshwater and can be of
three types:
A. Anadromous: These species have feeding areas in the
ocean and spend a major part of their lives in the sea
but they migrate to fresh water rivers for spawning .
Example : Salmon ,Pacific salmon ,Hilsa ,Petromyzon.
B. Catadromous: These fishes spend a major part of their
lives in fresh water but migrate long distances to the sea
for spawning .
Example :eel , Anguilla .

7. C. Amphidromous:These are diadromous fishes in which
migration from fresh water to sea or vice versa is not
for spawning as in others .But the migration occurs
regularly at some definite stage of the life cycle .
Example : Gobies
2. Potamodromous Fishes : Species whose migratory
movement remain confined to freshwater. These
species travel long distances in rivers to locate
suitable spawning grounds .After egg laying ,the
parents return to the feeding area .
Example :Cyprinids,clupeids,Catfishes,Salmon,Trout.

8. 3. Oceanodromous Fishes:
Fish species which show their migratory
movement within marine water , These are
truly migratory fishes which travel long
distances in the sea to spawn ,and later return
to the feeding areas.
Example : Herrings ,Cod, Tunas ,Flat fish

9. Causes of Migration
 To avoid unfavourable conditions .
To enhance the chances of survival of the
off -springs .
 To exploit the available food in feeding
areas.
Population pressure is also considered a
possible cause of migration .

10. Factors Influencing Migration
• Migration of fishes is initiated and influenced by
several physical ,chemical and biological factors .
• Physical factors : Temperature ,Light ,Intensity,
Photoperiod, Water current ,Turbidity .
• Chemical Factors : Ph ,Salinity, Odour.
• Biological Factors : Food , Memory ,Physiological
clock , Predators .

11. MCQ
• Which of the following fish are catadromous?
a. Fresh Water eel b. Tunas c. Salmon d.Herrings
• Which of the following fish are anadromous ?
a. Tunas b. Anguilla c. Salmon d. Mackerel
• Hilsa is ?
a. Catadromous b. Anadromous c . Potamodromous
• Oceanodromous fishes migrate from ?
a. Sea to river b. River to sea c. Within sea d. Within river