Fish Migration

Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Fish usually migrate to feed or to reproduce, but in other cases the reasons are unclear.

Migrations involve the fish moving from one part of a water body to another on a regular basis. Some particular types of migration are anadromous, in which adult fish live in the sea and migrate into fresh water to spawn, and catadromous, in which adult fish live in fresh water and migrate into salt water to spawn.

Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Movements are associated with ocean currents and with the availability of food in different areas at different times of year. The migratory movements may partly be linked to the fact that the fish cannot identify their own offspring and moving in this way prevents cannibalism. Some species have been described by the United Nations Convention on the Law of the Sea as highly migratory species. These are large pelagic fish that move in and out of the exclusive economic zones of different nations, and these are covered differently in the treaty from other fish.

Salmon and striped bass are well-known anadromous fish, and freshwater eels are catadromous fish that make large migrations. The bull shark is a euryhaline species that moves at will from fresh to salt water, and many marine fish make a diel vertical migration, rising to the surface to feed at night and sinking to lower layers of the ocean by day. Some fish such as tuna move to the north and south at different times of year following temperature gradients. The patterns of migration are of great interest to the fishing industry. Movements of fish in fresh water also occur; often the fish swim upriver to spawn, and these traditional movements are increasingly being disrupted by the building of dams.

1. FISH MIGRATION Presented By: Anwar Ullah BS-Zoology 7 th Semester

2. Introduction Migration - The directed movement of large number of animals from one place to another for various reasons . Or This synchronous, directed movement of part or all of a population between discrete( Separate) habitats is called “migration” 2 .5 % of All fishes are Migratory in Nature. Migration – from hundred meters ( e.g coastal & stream dwelling fishes) to Thousands of Kilometer ( e.g Eels) Successful Migration: Motivation, Energy Storage , Locomotion Ability .

3. Why do Fish migrate? (Reasons) Several Reasons: For New Suitable Habitat. (To avoid unfavorable conditions) For Feeding– Food Searching For Reproduction & Spawning. (To enhance the survival of offspring's) Some Fishes Migrate in Order to Escape from Predators .

4. Types of Fish Migration On the basis of Food, Spawning, Climate & Water Current : These Include the Following; Feeding Migration: Migration of fish in search of food & water is called Feeding Migration. This occurs because the supply of food in any habitat is not constant, fluctuates from time to time . Grow fast in size & mature & produce more eggs. Better food facilities, better survival & fast growth Examples : cyprinids, Salmonids , Percids

5. Cyprinids : Puntius titteya S almonids Percidae

6. 2. Spawning Migration Migration for the purpose of Spawning- Spawning Migration.( Spawning :Producing eggs in large numbers) More Prominent as compared to others because – aggregation of thousand of fishes to a particular habitat. Examples: Salmonids, Osmeridae , cyprinids, castostomids Osmeridae (Smelt) Cyprinids : Puntius titteya Catostomidae : Suckers

7. 3. Climate & Refuge Seeking Migration Migration in response to harsh climate condition. Arctic (of ice) & subarctic Fishes Migrate. Examples: Thymallus arcticus , Salvelinus alpinus Anguilla anguilla : Migrate in order to avoid ground ice , surface ice & cold water. Arctic grayling : Thymallus arcticus Arctic char  or  Arctic charr  ( Salvelinus alpinus )

8. European eel: ( Anguilla Anguilla )

9. 4. Contranatant Migration Movement of Migratory fishes against the water current. (The movement of water from one location to another) 5. Detanatant Migration Movement of migratory fishes in the direction of water .

10. Types of Migration (2. On the basis of direction) Anadromous Catadromous Amphidromous

11. A. Diadromous Migration: Fish Migration Between Sea & Freshwater for SPAWNING (laying Eggs). Three Types: Anadromous Migration ( Sea to FW) Catadromous Migration ( FW to Sea) Amphidromous Migration Dia : across , Dromous : Path , way

12. Anadromous Fishes which migrate from the sea into fresh water to spawn ‘OR’ Ones which stay entirely in sea water and migrate upstream to spawn An 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 Common examples - Salmon , Trout, Hilsa, striped bass, Sea lamprey and sturgeon Salmon

13. striped bass Sea Lamprey sturgeon

14. Life History of salmon Salmon hatch in small freshwater streams . From there they migrate to the sea to mature ( 1 to 5 years ) . When mature, the salmon return to the same streams where they were hatched to spawn .

15. Al e v i n F r y Sm o lt Adult Spawner Spawning beds in FW SPAWN Adults change significantly once they enter freshwater. They change color, stop eating, males develop a kype (hooked jaw), and they stop drinking Entering fresh water After spawning spawners die Death Average number of eggs deposited per female is Egg around 3,000 eggs, 2-3 months for hatching Young free- swimming, 1-2 inches, learn to feed Parr (Young Salmon before it leaves FW. 2-5 inches , Parr marks, As salmon mature into a smolt , the Parr marks disappear When salmon prepare to migrate from freshwater to the ocean, they become smolts, spend some time in estuaries before heading to the ocean Salmon spend 1-5 years in the ocean, 80% of their life cycle Entering into Sea water Remain in the gravel for another 1-2 months, yolk sac

16. 2. CATADROMOUS Catadromous fishes are ones which migrate from fresh water into the sea to spawn ‘OR’ Ones which stay entirely in fresh water and migrate downstream to spawn . Best examples - eels of the genus Anguilla , numbering 16 species, the best-known of which are the North American eel ( A. rostrata ) and the European eel ( A. anguilla )

17. Co n t ’ d… It travels several thousand km starting from rivers reaching spawning grounds in sea . After spawning adults die . Young ones are born in the ocean, mature in freshwater or estuarine habitats, and return to the ocean to spawn . This makes them Catadromous fish

18. Eel life cycle

19. 3. Amphidromous Migration: Migration of fishes from sea to rivers & vice versa, but not for breeding purpose. Mainly for food & change of environment. Example: Gobies

20. These are born in freshwater/estuaries, then drift into the ocean as larvae before migrating back into freshwater to grow into adults and spawn

21. B. PO T AMO D ROMO U S The movement is limit only to fresh water . Lake: (Lake trout - Salvelinus namaycush ) Rivers & Streams: ( brook lamprey - Lampetra spp ) Lake & fluvial habitats: ( white suckers , Catostomus commersoni ) Travels long distances in rivers to locate suitable spawning grounds (Some migrates Upstream and some downstream ) After laying eggs, the parents return to the feeding area as food is available only for the young ones & cannot support the adults

22. Co n t ’ d… Besides spawning needs, this type of migration may also be due to competition , Such as increase in population . Scarcity of food may also force fishes to migrate other places, where food is abundant .

23. LAKE TROUT brook lamprey white suckers

24. Potamodromous fish are born in upstream freshwater habitats, then migrate downstream (still in freshwater) as juveniles to grow into adults before migrating back upstream to spawn

25. C. OCEANODROMOUS These are truly migratory marine fishes . 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 . During migration these species visit spawning areas, nursery areas, feeding areas, winter area etc . Examples: Mackerels, Tunas, Cod, Herrings

26. Tunas Cod  Atlantic mackere

27. fish are born near spawning grounds, then drift on ocean currents as larvae before settling as juveniles to grow into adults before migrating back to spawning grounds.

28. Factors influencing migration Influenced by several Physical, Chemical, and Biological factors Physical factors Temperature Light intensity Photoperiod Water current Turbidity depth Temperature is of more importance, in sea water rise in temperature provides stimulus to Salmon for Migration. In fresh water temperature rise fishes moves upstream for spawning .

29. Chemical factors Chemical factors pH Salinity Odour 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 etc., are euryhaline and can adjust to large salinity variations i.e. Diadromous fishes

30. Biological factors Biological factors Food Memory Stage of sexual maturity Predators and competitors 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

31. Advantages of fish migration Fish get more food, better climatic condition and breeding place Fish gets better adapting in new places. There will be wide distribution. Less competition.

32. Disadvantages of fish migration Chances of loss of life due to the shortage of food for predators of higher forms, earthquake, tsunami, cyclone etc Mant migratory birds are exposed to innumerable risks during traveling and die in tremendous numbers They are killed by sudden changes in temperature in weather such as heavy rainfall or snowfall or stormy wind. They are killed by hawks & man during migration.

33. JazakALLAH ANY QUESTION ?