MIGRATION IN FISHESMIGRATION IN FISHES

Sameer G. ChebbiSameer G. ChebbiIndustrial fish and fisheriesIndustrial fish and fisheriesDept. of ZoologyDept. of ZoologyKarnatak Science College, DharwadKarnatak Science College, Dharwad

IntroductionIntroduction Migration is the movement of large number of Migration is the movement of large number of

animals from one place to another for feeding, animals from one place to another for feeding, reproduction or to escape weather extremes. reproduction or to escape weather extremes. When large numbers of fishes come together When large numbers of fishes come together and move socially it is called and move socially it is called shoaling.shoaling.

But sometimes migrating fishes exhibit high But sometimes migrating fishes exhibit high degree of coordination in their movements and degree of coordination in their movements and carry out synchronized manoeuvres to produce carry out synchronized manoeuvres to produce different types of shapes.  different types of shapes.  

This is called This is called schooling, schooling, as seen in tunas and as seen in tunas and sardines.sardines.

Diadromons fishesDiadromons fishes – migrate between sea  – migrate between sea & fresh water& fresh water AnadromousAnadromous – major part sea but fresh water  – major part sea but fresh water

during breeding season e.g. Salmon & Hisladuring breeding season e.g. Salmon & Hisla CatadromousCatadromous – major part fresh water but sea  – major part fresh water but sea

during breeding e.g. Anguilla (eel fish)during breeding e.g. Anguilla (eel fish) AmphidramonsAmphidramons – fresh water to sea & vice  – fresh water to sea & vice

versa. Eg. Gobiesversa. Eg. Gobies PotamodromonsPotamodromons – migratory, confined to  – migratory, confined to

fresh water eg. Corps and trouts, Mahasees fresh water eg. Corps and trouts, Mahasees move up stream along Himalaya riversmove up stream along Himalaya rivers

Oceanodromons Oceanodromons – migratory, confined to – migratory, confined to sea only eg. Tunnas, Mackerelssea only eg. Tunnas, Mackerels

Causes of migration in fishesCauses of migration in fishes Heape (1961) – 4 primary reasons of fish migrationHeape (1961) – 4 primary reasons of fish migration Gametic migrationGametic migration (Spawning/breeding migration) (Spawning/breeding migration)

Better survival & proper development of egg/larvaBetter survival & proper development of egg/larva Stop feeding prior to migration or reduced drasticallyStop feeding prior to migration or reduced drastically Energy requirement (fat deposit) e.g. Chum salmon spp. 25,810 Ca & Energy requirement (fat deposit) e.g. Chum salmon spp. 25,810 Ca &

28,390 cal by male and female respectively28,390 cal by male and female respectively Alimental of Feeding MigrationAlimental of Feeding Migration

Due to shortage of food (Suitable/wintering/spawing)Due to shortage of food (Suitable/wintering/spawing) Better food facilities, better survival & fast growthBetter food facilities, better survival & fast growth Grow fast in size & mature & produce more eggs.Grow fast in size & mature & produce more eggs.

Climate or Wintering MigrationClimate or Wintering Migration Due to inactive physical condition and low BMR (Basic Metabolic rate)Due to inactive physical condition and low BMR (Basic Metabolic rate) Depends on fish condition and environmentDepends on fish condition and environment Achieved by hormonal and physiological changesAchieved by hormonal and physiological changes Deposit mainly as fat depositsDeposit mainly as fat deposits Among freshwater species (Grass corp.) more to wintering grounds.Among freshwater species (Grass corp.) more to wintering grounds.

Osmoregulatory or Protective MigrationOsmoregulatory or Protective Migration Spwing, feeding & wintering migration can all be regards as protection Spwing, feeding & wintering migration can all be regards as protection

migration as they ensure further life of fishmigration as they ensure further life of fish These migration are not cyclicalThese migration are not cyclical

Methods of studyMethods of study Marking and tagging (Scale marking or removal)Marking and tagging (Scale marking or removal) Fisheries statistics (different areas at specific time)Fisheries statistics (different areas at specific time) Echo ranging techniques (modern & accurate)Echo ranging techniques (modern & accurate)

Similar to echo location in bats by ultra sound emitted in small shipSimilar to echo location in bats by ultra sound emitted in small ship Indicates presence of shoals and depth at which presentIndicates presence of shoals and depth at which present

Direct observation (Land, ship or aircraft)Direct observation (Land, ship or aircraft) Marking and TaggingMarking and Tagging Physical MarkingPhysical Marking

Caught and clip finsCaught and clip fins Used for short term onlyUsed for short term only

Internal MarkingInternal Marking Metallic marking introduced within the body cavity by marking gunsMetallic marking introduced within the body cavity by marking guns Electro marking detectors & prevent from connivingElectro marking detectors & prevent from conniving

External MarkingExternal Marking Body surfaces or gill over or pretention boseBody surfaces or gill over or pretention bose Two celluloid disc esp. Flat fishesTwo celluloid disc esp. Flat fishes

Lea hydrostatic taggingLea hydrostatic tagging Used for long distance migrants like codsUsed for long distance migrants like cods Small celluloid cylinder, remains hermetically sealedSmall celluloid cylinder, remains hermetically sealed Information kept (address)Information kept (address)

Numbered boit hook taggingNumbered boit hook tagging Red fish & deep sea fishes are usedRed fish & deep sea fishes are used When brought up diaWhen brought up dia

Plastic flag taggingPlastic flag tagging Used in codsUsed in cods Attached in back of fish by braided nylon threadAttached in back of fish by braided nylon thread

Feeding or alimental Feeding or alimental migrationmigration

Feeding or alimental migration Feeding or alimental migration takes place in takes place in fishes for feeding. fishes for feeding.

In high populations fishes exhaust food In high populations fishes exhaust food resources in an area quickly and therefore resources in an area quickly and therefore must migrate constantly in search of new must migrate constantly in search of new feeding resources. feeding resources.

Salmons, cods and sword fish constantly Salmons, cods and sword fish constantly migrate for food from one place to another in migrate for food from one place to another in the sea.the sea.

Spawning migrationSpawning migration Spawning migration Spawning migration takes place in takes place in

breeding season in those fishes which breeding season in those fishes which have spawning grounds far away from have spawning grounds far away from feeding places. feeding places.

Migratory fishes such as eels and Migratory fishes such as eels and salmons and a large number of riverine salmons and a large number of riverine fishes spawn in tributaries of river in hills fishes spawn in tributaries of river in hills and migrate in large number for laying and migrate in large number for laying eggs in these oxygen rich waters. eggs in these oxygen rich waters. 

Juvenile migration Juvenile migration involves larval stages involves larval stages of fishes which hatch in spawning grounds of fishes which hatch in spawning grounds and must migrate long distances in order and must migrate long distances in order to reach the feeding habitats of their to reach the feeding habitats of their parents.parents.

Recruitment migration Recruitment migration takes place when takes place when large number of larvae moves from large number of larvae moves from nursery habitat to the habitat of adults nursery habitat to the habitat of adults which may sometimes be distinctly which may sometimes be distinctly different. Adults of eels live in rivers in different. Adults of eels live in rivers in Europe and America but their larval stages Europe and America but their larval stages live and grown in sea and migrate to reach live and grown in sea and migrate to reach rivers which may take one to two years.rivers which may take one to two years.

Seasonal migrationSeasonal migration Seasonal migration Seasonal migration takes place in takes place in

fishes that inhabit arctic areas where in fishes that inhabit arctic areas where in summer climate is conducive and food summer climate is conducive and food abundant but as winter approaches abundant but as winter approaches temperatures fall below zero and food temperatures fall below zero and food becomes scarce. becomes scarce.

Hence fishes must migrate towards Hence fishes must migrate towards subtropical and tropical areas to escape subtropical and tropical areas to escape extremes of weather conditions.extremes of weather conditions.

TYPES OF MIGRATION IN TYPES OF MIGRATION IN FISHESFISHES

Fishes live in two different types of Fishes live in two different types of aquatic habitats, namely, freshwater and aquatic habitats, namely, freshwater and marine habitats, which pose different marine habitats, which pose different osmotic problems because of which it is osmotic problems because of which it is difficult to migrate from one type of difficult to migrate from one type of habitat to another. habitat to another. 

Nevertheless, some fishes do migrate.Nevertheless, some fishes do migrate.

POTAMODROMOUS MIGRATIONPOTAMODROMOUS MIGRATION When fishes migrate from one freshwater habitat When fishes migrate from one freshwater habitat

to another in search of food or for spawning, it is to another in search of food or for spawning, it is called potamodromous migration. called potamodromous migration.

There are about 8,000 known species that There are about 8,000 known species that migrate within lakes and rivers, generally for migrate within lakes and rivers, generally for food on daily basis as the availability of food food on daily basis as the availability of food differs from place to place and from season to differs from place to place and from season to season. season.

Fishes also must migrate to lay their eggs in Fishes also must migrate to lay their eggs in places where oxygen concentration in water is places where oxygen concentration in water is more and where there is abundance of food for more and where there is abundance of food for juveniles when they hatch from eggs.juveniles when they hatch from eggs.

OCEANODROMOUS MIGRATIONOCEANODROMOUS MIGRATION This migration is from sea water to sea water. This migration is from sea water to sea water.

There are no barriers within the sea and fishes There are no barriers within the sea and fishes have learned to migrate in order to take have learned to migrate in order to take advantage of favourable conditions wherever advantage of favourable conditions wherever they occur. they occur.

Thus there are about 12,000 marine species that Thus there are about 12,000 marine species that regularly migrate within sea water. regularly migrate within sea water.

Herrings, sardines, mackerels, cods, roaches Herrings, sardines, mackerels, cods, roaches and tunas migrate in large numbers in search of and tunas migrate in large numbers in search of food by way of food by way of shoaling shoaling (migrating together (migrating together socially but without much coordination) socially but without much coordination) or or schooling schooling (swimming with high degree of (swimming with high degree of coordination and synchronized manoeuvres).coordination and synchronized manoeuvres).

DIADROMOUS MIGRATIONDIADROMOUS MIGRATION   When fishes can migrate from fresh water When fishes can migrate from fresh water

to sea or from sea to fresh water, it is to sea or from sea to fresh water, it is called diadromous migration. called diadromous migration.

There are about 120 species of fishes that There are about 120 species of fishes that are capable of overcoming osmotic are capable of overcoming osmotic barriers and migrate in these two different barriers and migrate in these two different types of habitats. This migration is of two types of habitats. This migration is of two types.types.

Catadromous migrationCatadromous migration Anadromous migrationAnadromous migration

Catadromous migrationCatadromous migration This type of migration involves movement of This type of migration involves movement of

large number of individuals from fresh water to large number of individuals from fresh water to sea water, generally for spawning as happens in sea water, generally for spawning as happens in the case of eels the case of eels (Anguilla) (Anguilla) inhabiting European inhabiting European and North American rivers.and North American rivers.

  Both European eel Both European eel (Anguilla anguilla (Anguilla anguilla or or Anguilla Anguilla vulgaris) vulgaris) and the American eel and the American eel (Anguilla (Anguilla rostrata) rostrata) migrate from the continental rivers to migrate from the continental rivers to Sargasso Sea off Bermuda in south Atlantic for Sargasso Sea off Bermuda in south Atlantic for spawning, crossing Atlantic Ocean during the spawning, crossing Atlantic Ocean during the journey and covering a distance of about 5,600 journey and covering a distance of about 5,600 km. km.

The adult eels that inhabit rivers are about a The adult eels that inhabit rivers are about a metre long, yellow in colour and spend 8-15 metre long, yellow in colour and spend 8-15 years feeding and growing. years feeding and growing.

Before migration the following changes take Before migration the following changes take place in their bodies:place in their bodies:

They deposit large amount of fat in their bodies They deposit large amount of fat in their bodies which serves as reserve food during the long which serves as reserve food during the long journey to Sargasso Sea.journey to Sargasso Sea.

Colour changes from yellow to metallic silvery Colour changes from yellow to metallic silvery grey.grey.

Digestive tract shrinks and feeding stops.Digestive tract shrinks and feeding stops. Eyes are enlarged and vision sharpens. Other Eyes are enlarged and vision sharpens. Other

sensory organs also become sensitive.sensory organs also become sensitive. Skin becomes respiratory.Skin becomes respiratory. Gonads get matured and enlarged.Gonads get matured and enlarged. They become restless and develop strong urge They become restless and develop strong urge

to migrate in groups.to migrate in groups.

They migrate through the rivers and reach coastal areas They migrate through the rivers and reach coastal areas of the sea where they are joined by the males and then of the sea where they are joined by the males and then together they swim in large numbers, reaching Sargasso together they swim in large numbers, reaching Sargasso Sea in about two months. They spawn and die. Each Sea in about two months. They spawn and die. Each female lays about 20 million eggs which are soon female lays about 20 million eggs which are soon fertilized by males.fertilized by males.

First clue about life cycle of eels was given by two Italian First clue about life cycle of eels was given by two Italian scientists Grassi & Calandruccio in 1896.  Details of scientists Grassi & Calandruccio in 1896.  Details of migration and life cycle were later studied by Johann migration and life cycle were later studied by Johann Schmidt (1905). Eggs hatch into leaf-like, Schmidt (1905). Eggs hatch into leaf-like, semitransparent, larvae having small head semitransparent, larvae having small head calledcalledLeptocephalus. Leptocephalus.  Leptocephali of American eels  Leptocephali of American eels take about 10 months to fully grow while those of take about 10 months to fully grow while those of European eels take about 18 months. Upon reaching European eels take about 18 months. Upon reaching coastal waters leptocephali metamorphose into another coastal waters leptocephali metamorphose into another larval stage called larval stage called Elver Elver or Glass eel. Female elvers or Glass eel. Female elvers ascend to the rivers and metamorphose into yellow-ascend to the rivers and metamorphose into yellow-coloured adults, while males stay back in the river mouth coloured adults, while males stay back in the river mouth and wait for the females to return for spawning journey.and wait for the females to return for spawning journey.

Anadromous migrationAnadromous migration   Adults of anadromous fishes live and feed in Adults of anadromous fishes live and feed in

ocean waters but their spawning grounds lie in ocean waters but their spawning grounds lie in the tributaries of rivers. Salmons, sturgeons, the tributaries of rivers. Salmons, sturgeons, Hilsa and lampreys are some of Hilsa and lampreys are some of the marine fishes that undertake anadromous the marine fishes that undertake anadromous migration to spawn in rivers.migration to spawn in rivers.

Atlantic salmon Atlantic salmon (Salmo salar) (Salmo salar) migrates to the migrates to the North American rivers for spawning while six North American rivers for spawning while six species of Pacific species of Pacific salmonsalmon(Onchorhynchus) (Onchorhynchus) migrate to various migrate to various rivers of Asian countries.rivers of Asian countries.

Salmons living in sea are metallic silvery grey in colour Salmons living in sea are metallic silvery grey in colour but before migration they turn reddish-brown in colour. but before migration they turn reddish-brown in colour. During fall, they enter rivers and swim During fall, they enter rivers and swim energetically against water currents energetically against water currents ((contranatentcontranatent), clearing all obstacles, including ), clearing all obstacles, including waterfalls and reach tributaries in hilly areas where they waterfalls and reach tributaries in hilly areas where they make a saucer-like pit in which female lays eggs and make a saucer-like pit in which female lays eggs and male releases smelt over them. male releases smelt over them. 

Eggs take 2-3 months to hatch in the following spring, Eggs take 2-3 months to hatch in the following spring, when the juvenile stage called when the juvenile stage called Alvin Alvin emerges out but emerges out but remains within the nest, obtaining its nourishment from remains within the nest, obtaining its nourishment from the yolk sac attached to its belly. the yolk sac attached to its belly. 

Alvin then transforms into Alvin then transforms into Fry Fry which feed on planktons. which feed on planktons. Fries are Fries are denatantdenatant (they swim along with water current)  (they swim along with water current) and feed and grow into fingerlings which take the shape and feed and grow into fingerlings which take the shape of adult fish. They change into of adult fish. They change into SmoltSmolt  which congregate   which congregate at the river mouth in large numbers and then enter at the river mouth in large numbers and then enter sea water in to metamorphose into adult salmons.sea water in to metamorphose into adult salmons.